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Java CardTM & STK Applet
Development Guidelines
Version 1.0
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Table of content
1 Introduction........................................................................................................................... 4
1.1 Purpose.......................................................................................................................... 4
1.2 BEWARE........................................................................................................................ 4
2 Applet Development ............................................................................................................... 5
2.1 Process for Applet Deployment ........................................................................................ 5
2.1.1 Service definition ......................................................................................................5
2.1.2 Service development ................................................................................................ 5
2.1.3 Application validation ................................................................................................ 5
2.1.4 Application deployment ............................................................................................. 5
2.1.5 Application maintenance ........................................................................................... 6
2.2 Applet Development Stages............................................................................................. 7
2.2.1 Off-card applet development ..................................................................................... 7
2.2.2 Java CardTM source code............................................................................................ 7
Application Identifier ........................................................................................................... 8
CLA and INS bytes .............................................................................................................. 9
Compiling source code ........................................................................................................ 9
Converting binary code........................................................................................................ 9
JCA, JAR, CAP and IJC files.................................................................................................. 9
EXP file .............................................................................................................................. 9
2.2.3 On-card process...................................................................................................... 10
Loading the package ......................................................................................................... 10
Install (Load) command .................................................................................................... 11
Load command ................................................................................................................. 11
Installing an applet ........................................................................................................... 12
Creating an applet instance ............................................................................................... 12
Parameters common to any applet instance: ...................................................................... 12
Parameters specific to STK applet ...................................................................................... 12
Registering an applet and making it selectable.................................................................... 13
Allocation of the on-card resources .................................................................................... 14
2.2.4 Managing on-card applet instance............................................................................ 15
Setting applet status ......................................................................................................... 15
Selecting a Java CardTM applet........................................................................................... 15
Triggering a STK applet..................................................................................................... 16
Deleting applet instances or library packages...................................................................... 16
Retrieving applet data ....................................................................................................... 16
2.3 Applet Development Environment................................................................................... 17
2.3.1 Why using JAVATM development environment?.......................................................... 17
2.3.2 Java CardTM security................................................................................................ 17
2.3.3 Applet runtime environment .................................................................................... 18
2.3.4 Java CardTM Virtual Machine..................................................................................... 18
2.3.5 Java CardTM API ...................................................................................................... 18
2.3.6 3GPP TS 43.019 API................................................................................................ 19
2.3.7 JCRE support services ............................................................................................. 19
2.4 Writing a Toolkit Applet.................................................................................................. 20
2.4.1 Overview of a toolkit applet architecture................................................................... 20
2.4.2 Example of applet ................................................................................................... 20
2.4.3 Limitations in an applet creation .............................................................................. 23
2.5 Developer Suite as a Java Card IDE............................................................................... 24
3 Basic Development Rules..................................................................................................... 25
4 Recommendations to minimize risks in field........................................................................... 33
5 Anti-Tearing recommendations ............................................................................................. 40
5.1 Reminder on anti-tearing mechanism.............................................................................. 40
5.1.1 Atomicity on objects' field updating .......................................................................... 40
5.1.2 Transaction services............................................................................................... 40
5.1.3 Embedded services using transaction services......................................................... 40
5.1.4 By-passing the on-going transaction may be necessary ............................................ 41
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5.2 Architecture overview .................................................................................................... 41
5.2.1 Level 1 ­ Backup module ........................................................................................ 41
5.2.2 Level 2 ­ Atomicity and transaction services provided by Java Card .......................... 42
5.2.3 Level 3 ­ Use of transaction services by applications ................................................ 42
5.3 Guidelines to protect applications against card tear-out.................................................... 42
5.3.1 Optimization of transaction critical section ................................................................ 42
5.3.2 Protection of transaction critical section.................................................................... 43
5.3.3 Protecting objects' allocations .................................................................................. 44
5.4 Recommendations for specific and proprietary APIs ........................................................ 46
5.4.1 Protecting the use of `object de-allocation'................................................................ 46
6 Application development Checklist ........................................................................................ 47
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1 Introduction
1.1 Purpose
The aim of this document is to provide guidance in the development of your java card applet. The
very mandatory and basic things to be known and done for such a development are described
below, and you will find a checklist at the end of this document that you can use for each of your
projects.
The document also aims at describing a Java CardTM code sensitive to card tear-out and at
providing related development guidelines. Not taking those rules into account may lead to
severe damage since the cards on the field may become out of order with according
consequences for customers and the company
This document focuses on Java Card especially and assumes the reader knows basic Java
programming thus will not be covering Java programming syntax and coding techniques.
1.2 BEWARE
The Java and Java Card memory models are different and are therefore requesting different
ways of design.
EEPROM is stressed each time you use it and the number of time you can update an
EEPROM cell is limited (guaranteed 100,000 updates for E2PROM and FLASH
technologies).
In the meantime, RAM space is very limited in Java Card memory models compared to Java
memory model.
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2 Applet Development
2.1 Process for Applet Deployment
Value added services are implemented on the Java card in the form of applets.
The applets have to be developed by the application developers and load into the card using the
appropriate commands. When you need to develop an applet you must remember:
To use the classes defined in TS 43.019, Java CardTM 2.1.1
To use only the subset of the JavaTM language defined in the Java CardTM 2.1.1
standards.
The process from service definition to application deployment is briefly described in the following
parts.
2.1.1 Service definition
The services are defined by the mobile communication operator or other service providers.
Gemalto can offer a consulting role in this definition process. These services are based on:
Standard GSM, and Telecom features and functions:
Toolkit functions
Functions specific to the operator or service provider
Over The Air services
The card supports the APDU commands defined in 3GPP 51.011, as well as toolkit commands
defined in 3GPP 51.014.
2.1.2 Service development
An operator, a service provider, a software house or Gemalto is allowed realizing the service
development. Development is easily achieved by performing the following steps:
Prototype the service.
Program and compile an application in any standard JavaTM development environment.
On your PC, prepare the compiled application for loading onto the card. Define any
application specific files (e.g., application PIN code file) and configure the application
data.
From your PC, load the application, its files and its configuration data onto the card.
2.1.3 Application validation
Before an application is deployed in the field to subscribers it must be certified to ensure that it is
bug free and respects the functional and security requirements of the operator. Currently it is
anticipated that only the operator or Gemalto can perform the role of certifying applications.
2.1.4 Application deployment
Applications can be deployed at any time during the life cycle of the card. Applications can be
loaded:
By Gemalto at the factory
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In the mobile using OTA customization
From a terminal at the point of sale, from a PC via the web...
2.1.5 Application maintenance
Application maintenance can be broken into three categories:
Modification of application data (e.g., menu texts, send SMS contents, text to be
displayed)
Modification of application files (e.g., application PIN code value)
Update of application functionality (e.g., add a new menu). In this case the applet code
has to be deleted and the updated code loaded.
In the same way as applications can be loaded, they can be deleted. The card allows application
free space to be re-used thanks to the DMM mechanism (see the User's guide).
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2.2 Applet Development Stages
An application passes different distinct stages of development, and life cycle states within the
card. These are divided into two phases, off-card and on-card, related to the physical
environment.
2.2.1 Off-card applet development
The off-card phase includes:
Developing in Java CardTM language with the client terminal program (source code java
file)
Compiling (byte code class file and exp files)
Converting into a format that can be loaded into JavaTM cards (JAR or IJC files).
Figure 1 - Off-card applet development
2.2.2 Java CardTM source code
An applet loaded into the card provides the end-user with a set of services. These are activated
in response to requests from the end-user or the client terminal. The client application in the
terminal interacts with the applet as follow:
The client application implements functions
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The application uses APDU commands to send parameters to the applet.
The applet sends a response that is received by the client application.
The client application analyses the carďs response.
The source code can define two sorts of applets:
The Java CardTM applets, created in compliance to the Java CardTM standards v 2.1.1.
These applets use the Java CardTM APIs, which provide basic services common to any
Java CardTM applet, such as:
Handling the APDUs independently from the protocol used (T = 0 or T = 1)
Managing security (signature, encryption, decryption, decryption, key, PIN)
The APIs also provide utility services such as transactions or transient object creation.
In the rest of this documentation, this kind of applet will be called "Java CardTM applet".
The Java CardTM SIM Toolkit applet is a Java CardTM applet created in compliance to the
TS 43.019 standard. This standard extends the Java CardTM v2.1.1 standards to allow
the SIM card issuing pro-active commands and performing actions on the file's system.
In the rest of this documentation, this kind of applet will be called "STK applet".
The term "applet" will be dedicated to any of the kinds described above.
Within the source code, the following values have to be defined:
Application Identifier (AID) is used for matching the applet with its client applications.
CLA and INS bytes are used in APDU commands invoked by the clienťs terminal
methods. These methods and APDU commands depend on the appleťs functionality.
Application Identifier
Both packages and applets are identified with their application identifier (AID). This is included in
the code of the applet and the client application, enabling a client application to target its
corresponding application.
The AID is defined in ISO 7816-5. It is a byte string from 5 to 16-byte length. The identifiers are
administered by ISO. You must register an application with ISO in order to get an official and
unique AID. The application provider may also obtain a registered application provider identifier
(RID) from ISO. The AID is constructed as shown in the following figure. The RID bytes are
followed by 11 bytes that can be freely assigned by the application provider.
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Figure 2 - Structure of GSM AID
CLA and INS bytes
CLA byte represents a class of instructions. During execution, the applet verifies the CLA byte of
an APDU command. Refer to ISO 7816-3 for more information about the class byte definition.
INS byte represents a particular instruction. It is declared at the beginning of the client
application, which defines all the functionality of the applet.
Compiling source code
The source code must be compiled with a Java CardTM compliant compiler. The compiled source
code is known as the binary code (class file).
Converting binary code
The binary code must be converted with a Java CardTM compliant converter. It transforms the
binary format (class file) into a file format that can be loaded into the card. The converter allows
to either convert a package alone (with no applet inside) or to convert a package and set the
applet AID of the class that defines the applet.
Note: some tools (for example jcconverter and jar2cap) can be used to optimize the conversion.
The conversion is a two-step process that produces first a jca file (Java Card Assembly file) and
an exp file (export file), then the jar and cap/ijc files (also known as Load File or package).
If you are using the Gemalto Developer Suite, (section 2.5) these conversion tools are
embedded into the tool.
JCA, JAR, CAP and IJC files
The jca file is an ASCII file to aid testing and debugging. It is used to produce the jar file, created
when a package of classes is converted.
The jar file is the Java Card byte code to be loaded in the card. It can be seen as a "zip" file,
which contains a set of CAP files (Converted Applet files). Each CAP file is a component, which
describes an aspect of the executable code to be downloaded.
IJC tools are widely available. If you are using the Gemalto Developer Suite, (section 2.5) there
is an embedded component jar2ijc which is used to generate your IJC file.
Since IJC files are much smaller in size this allows gaining bandwidth when downloading Over
The Air.
Note: the ijc file concatenates the CAP files in one file only, following the reference component
order (described in the JCVM 2.1.1 standard) to produce a binary file directly loadable on
the card.
EXP file
The exp file is created when the package is converted. It contains the information of the public
interface for the package of classes. The exp file is not used directly by the Java CardTM Virtual
Machine to execute the code. Nevertheless, it can be useful later to convert another package that
imports classes from the first package.
Note: if the package does not contain toolkit applet, the export file contains all public or protected
static methods and fields. If the package contains a toolkit applet, the exp file contains the
shareable interface, javacard.framework.Shareable or an interface which implements the
Shareable interface.
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2.2.3 On-card process
The Card Manager is responsible for all application installations. It owns and uses a card registry,
which holds information about the application life cycle states (see also the part "Setting applet
status"). The on-card process includes:
Loading the package
Installing an applet instance from the package
Making this instance selectable
Figure 3 - On-card process
Note that the on-card process is aborted and any partially downloaded package or installed
applet instance is deleted in the following cases:
Access conditions are not fulfilled.
Allocated EEPROM space is not sufficient.
An exception, reset, or power fail occurs while a step of the process is not ended.
Loading the package
Loading the package consist in loading a Load File (or package). This file is composed of two
blocks:
One DAP (Data Authentication Pattern) block (optional) mandated for the Card Manager
to perform a verification procedure (see below).
One Load File Data Block, which contains the content of the ijc file.
Figure 4 - Load File structure
The Load File is loaded by the use of two APDU commands:
Install APDU command in Load mode
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Load APDU command
If the EEPROM memory space is insufficient, the DMM mechanism is automatically triggered to
recover the memory needed.
Install (Load) command
The Install (Load) APDU instructs the Card Manager to initiate the loading and reserve the oncard
resources. More precisely, the data field of this command indicates:
The AID of the Load File. This value is checked by the Card Manager in order to ensure
that no other on-card entity has the same AID value.
The presence of the Load File DAP (optional property; do not confuse with the DAP
block!) used to ensure integrity of the Load File content. If present, the Card Manager
calculates a checksum, once the last block is received (last Load APDU command is
received), by using a XOR algorithm on 16 bits. The result is compared to the value of
the Load File DAP.
If the values are identical, the loading session continues.
If the values are different, the loading session is aborted and the Card Manager
recovers the on-card resources.
The size of the EEPROM memory (non-volatile memory) that the Card Manager must
reserve to load the Load File; that is the size needed to load the ijc file, the static objects
declared in the Load File (if present) and the DAP block (if present). If any, the DMM
mechanism is automatically triggered to recover the EEPROM memory needed. Note:
If this size value is set to 0, the Card Manager automatically reserves the
minimum memory needed once the ijc file is fully loaded (last Load APDU
command is received).
Using the makeijc tool with the ­verbose option allows retrieving the size of the
static objects.
Optionally, the size of EEPROM & RAM memories to request the Card Manager to check
memories is sufficient to install and run an applet instance from the loaded package.
Load command
The Load APDU command is used to download the Load File; that is the DAP block (if any) and
the Load File Data block (content of the ijc file).
Caution: this command must immediately follow the Install (Load) command, else the Load File
loading is aborted, and the Card Manager recovers all the on-resources previously
allocated.
According to the size of the Load File, several Load commands can be needed. The
blocks can be downloaded in any order except the first one, which must be received in
first (), and the last one, which must be received last. Once all blocks are received and
stored, the Card Manager proceeds to the mandated DAP verification procedure (if a
DAP block is present) and the package linking.
Note: the Card Manager is personalized such as the mandated DAP verification is mandatory
or optional. In the first case, the Card Manager aborts any package loading if the DAP
block is not included in the Load File, and an error Status Word is returned to the Load
command. In the second case, the Card Manager allows the package loading, even if
the DAP block is not include in the Load File.
The Card Manager proceeds to the DAP verification by using the DAP key coded on 8,
16 or 24 bytes and associated to a DES/TDES algorithm in Cipher Block Chaining
(CBC) with ICV of 8 bytes of binary zero.
Note: the DAP key has the key index 10h and is stored in ONE key set whose version is
defined during the carďs personalization phase.
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Installing an applet
Once the package is downloaded in the card, one or several applet instances can be installed.
Fully installing an applet instance can be seen as a three-step process:
Creating an applet instance by the way of the Install APDU command in Install mode.
Registering the applet instance.
Make the applet selectable by the way of the Install APDU command in Make Selectable
mode.
Creating an applet instance
The Install (Install) command requests the Card Manager to create ONE applet instance at once
from a downloaded package, and to allocate the on-card resources needed by this instance. The
on-card resources are:
EEPROM memory (non-volatile memory) to store persistent objects.
RAM memory (volatile memory) used to store the content of transient objects.
One free entry in the carďs registry.
Note: the GetData APDU allows retrieving the maximum amount of EEPROM memory the Card
Manager can allocate to the persistent objects.
The data field of the Install (install) command differs according to the kind of applet
instance:
Parameters common to any applet instance:
The AID value of the Load File, to allow the Card Manager identifying the package from
which the applet instance must be installed.
The AID within the Load File to allow the Card Manager retrieving the AID of the applet
defined in the Load File.
The AID of the applet instance to be installed (optional feature). The Card Manager
checks this value is not already used, as two on-card entities cannot have the same AID
value in the carďs registry. If this occurs, the command is aborted and the Card Manager
recovers all the on-card resources.
The size of the EEPROM memory (non-volatile memory) to be reserved to store the
persistent objects that the applet instance must create.
RAM memory (volatile memory) to be reserved to store the content of the transient
objects created by the applet instance. The Card Manager checks the free transient
memory is sufficient before reserving it. If it is not the case, the command is rejected.
Parameters specific to STK applet
When a STK applet instance is installed, some parameters specify the ME and SIM resources
that the applet can use:
The Access Domain
The Access Domain specifies the identities or access rights (CHV & ADM) granted to the
STK applet instance to access to the GSM files and perform actions on these files
according to their access conditions.
If all the access rights are granted, all actions are allowed except the ones with
the NEVER access conditions
If no access right is granted, no action is allowed.
If some access rights are granted, only the actions performed by the defined
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identities are allowed.
Defining an Access Domain for an applet instance is peculiar to this applet instance. This
implies:
Two STK applets instance installed from a same package can have different
access rights on the GSM system
The access rights of the STK applet instance are independent from the access
rights granted to an entity (user, OTA message) at the SIM/ME interface (see the
key set definition in the User's guide). For example, modifying the status of the
CHV1 (disabled, blocked) defined for the user at the SIM/ME interface does not
affect the CHV1 access right granted to a STK applet instance.
The priority level
The priority level defines which STK applet instance must be activated when two or more
STK applet instances have been registered to the same event. If STK applet instances
are registered to the same event with the same priority level, then the last instance
installed (the most recent one) is activated first.
The number of timers (maximum of 8, else the card returns the Status Word 6A80
"incorrect parameters", see the TS 51.011 standard)
The identifier of the menu entries
A unique item identifier can be defined for each STK applet instance to allow activating
the STK applet from its ME menu entry.
The card automatically allocates the position of the menu entries. The order of the menu
entries corresponds to the order of the registry entries which are free when the
installation occurs. For example, if the STK instance A is installed before the STK
instance B, its registry entry appears before the registry entry of the STK instance B. If an
STK instance C is installed and the STK instance B is removed, then the registry entry of
the STK instance A appears before the registry entry of the STK instance C and a free
registry entry is located between those of A and C. If the STK instance D must be
installed, the card searches for the first free registry entry that is, in this case, the entry
previously occupied by the STK instance B. So the order of the menu entries becomes A
D C.
The minimum security level
The minimum security level defines which level of security must be applied on the OTA
Command packets sent to the STK applet instance. This allows the STK applet instance,
once installed and selectable, checking the security level of each of the OTA message it
receives.
If the security level corresponds to the minimum required, the security of the
message is checked, and the STK applet instance processes the data.
If the security level does not correspond to the minimum required, the STK
applet instance rejects the OTA message. If required, a Response packet is
returned to the server.
Registering an applet and making it selectable
Registering the applet instance is mandatory to successfully end its installation and to allow it
being selectable.
The installation of the applet instance is considered complete upon successful return from one of
the following methods:
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register () method (used when the AID of the instance defined via the Install (Install)
APDU is the same as the AID within the Load File)
register (byte [], bArray; short bOffset, byte bLength) method (used when the AID of the
instance is provided in the INSTALL command parameters)
The applet instance is always registered with the value of the AID applet instance optionally
defined via the Install (Install) APDU.
Using the Install (make selectable) APDU instructs the Card Manager to allow the selection of an
applet instance via the SelectApplication APDU, and if it is a STK applet, from the triggering by
event.
Allocation of the on-card resources
Each new instance reserves spaces in the EEPROM and possibly in the RAM. This depends on
the content of the objects used by the applet instance when it is activated.
The content of an object is persistent if it remains unchanged on the card from one
session to another. This content is stored and referenced in the EEPROM memory as
long as the applet instance is not deleted.
The content of an object is transient when it does not persist from one session to the
next, and are reset to a default state at specified intervals. This allows using it to store
session keys. The content of a transient object is cleared to its default value (zero, false
or null) at the occurrence of the following events:
CLEAR_ON_RESET ­ the object content is used for maintaining states that
must be preserved across applet instance selections, but not across card resets.
CLEAR_ON_DESELECT ­ the object content is used for maintaining states that
must be preserved while the applet instance is selected, but not across applet
selections or card resets.
The transient contents are stored in RAM, but their references are in EEPROM.
The Card Manager allocates free transient memory differently according to the transient object
contents:
The CLEAR_ON_RESET object contents can never share RAM space. This means the
Card Manager deems the RAM space is not available anymore once the space is
already allocated to any of the transient object contents.
The CLEAR_ON_DESELECT object contents can share RAM space if and only if the
applet instances have not been installed from the same package.
When a new applet instance is installed, the Card Manager checks the free transient memory of
the RAM is sufficient to store the transient object contents of this new instance.
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Figure 5 - RAM space reserved to the transient object contents
For example, from the figure above:
If a new applet instance A3 must be installed, the S1 size is the free transient memory
checked by the Card Manager.
If a new instance B2 must be installed, the Card Manager checks the free transient
memory needed is not superior to S2, knowing that the CLEAR_ON_RESET object
content cannot use more than S1 free memory.
If a new instance C must be installed, the Card Manager checks the free transient
memory needed is not superior to S3, knowing that the CLEAR_ON_RESET object
content cannot use more than S1 free memory.
2.2.4 Managing on-card applet instance
Setting applet status
After personalization phase, the Card Manager owns and maintains the card life cycle state
information and manages the complete runtime environment. It is responsible for setting the
following application life cycle states:
Once the applet instance is installed on the card, its life cycle state is INSTALLED.
To be executed the life cycle state of an applet instance must be SELECTABLE.
To prevent any selection (and execution) of an applet instance, the life cycle state must
be set to LOCKED.
The appleťs life cycle state can be modified by use of the SetStatus command, with the P2
parameter indicating the new state:
03h = INSTALLED
07h = SELECTABLE. In this case, the applet instance is selectable via the
SelectApplication APDU or can be triggered from an event. Note if the instance is
registered to the MENU_SELECTION event, then it is included in the mobile menu
presented to the subscriber.
FFh = LOCKED. In this case, the applet instance is disabled. If it was registered to the
MENU_SELECTION event, then it is not included anymore in the mobile menu
presented to the subscriber.
Once the applet instance is available for selection or triggering from the outside world, it takes
control of managing its own life cycle. Nevertheless the Card Manager can still take control of the
application life cycle if a security problem is detected or if the applet instance has to be deleted.
Selecting a Java CardTM applet
A Java CardTM applet instance is selectable once it is correctly installed, registered within a
unique Application IDentifier (AID) and in the state SELECTABLE.
The SelectApplication APDU command is used to select a Java CardTM applet internally to the
card, with the data field of the command indicating the AID.
Once selected, the Java CardTM applet can access to the GSM file system and process the
APDU commands.
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Triggering a STK applet
A STK instance can be triggered once it is correctly installed, registered to events (see the next
chapter) and in the state SELECTABLE.
When triggered, the STK instance can access to the file system and process actions on these
files according to the access conditions defined on the files and the access domain defined for
the STK instance. From another part, the STK instance can send pro-active commands
according to the 3GPP 51.014 standard.
Note: when an applet is triggered via an OTA event, the initial context is restored including
previously logged identity once data are processed.
Deleting applet instances or library packages
Removing on-card packages and applet instances is allowed with the DeleteApplication command.
The command domain APPLET ADMIN must be granted to permit this action.
All the downloaded packages or installed applet instances can be deleted. The memory used by
the package or the instance is recovered as a free space and can be reused for a new
file/package/instance creation via the DMM mechanism (see the user's guide).
Note: a package cannot be deleted as long as one of its instances has not been deleted or if it is
imported by another applet instance.
Retrieving applet data
The card can supply information. The APDU commands used to retrieve data are summarized in
the following table:
APDU commands To retrieve data from:
GetData Card Resources
The card stores information on card resources such as:
Free EEPROM space
Number of installed applets
GetData Menu parameters and menu texts (for STK applet instance only)
The card stores the positions and identifiers for the menu entries of the
applets installed on the card:
Item position
Item identifier
Item text
Menu parameters are initialized during applet installation using the
Install(install) APDU command. Menu parameters cannot be modified
once the application has been installed.
Menu entries are initialized by the applet using the
sim.toolkit.ToolkitRegistry method initMenuEntry and can be changed
by using the ChangeMenuEntry method.
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GetData Application data of on-card resources (package or applet
instance)
Type of the on-card resource
Size of the on-card resource
Length and value of the Card Manager AID
Length and value of the package AID (applet instance only)
Access Domain (STK applet instance only)
Priority Level (STK applet instance only)
Security Level (STK applet instance only)
GetData Package Class AID
List the AID of each applet class defined in a package.
GetStatus Life Cycle Status of the Card Manager and the on-card resources
* AID
* Life cycle state
* Privileges (for applet instances only)
2.3 Applet Development Environment
In this chapter, you will find some Java CardTM programming basics to allow you developing a
simple application for the card. For a complete explanation, refer to the Java Card 2.1.1 and
3GPP 43.019 standards.
2.3.1 Why using JAVATM development environment?
JavaTM is an object oriented programming language developed by Sun Microsystems. This
language is designed to be platform independent.
The JavaTM language offers the following core advantages:
A standard programming language ­ anyone who knows how to write a JavaTM program
can write a smart program and load it onto a card.
Secure environment ­ JavaTM is well known as a secure programming language.
Multiple programs, or applets, on a card ­ the card architecture and the security features
of JavaTM language make it possible for multiple applets to reside safely on a card. The
number of applets is only limited by the amount of space on the card.
Full integration with mainstream JavaTM IDEs ­ the card software integrates most JavaTM
integration development environments.
All the benefits of object-oriented programming ­ programmers have the benefits of code
reuse, design patterns, and superior structure.
Platform independence ­ since JavaTM smart card programs are portable across different
chip architectures, applets cost less to develop and maintain.
Dynamic updates ­ you can develop and deploy applets incrementally, adding features
as you go along. You can add or delete the applets on a card at any point of its life cycle.
2.3.2 Java CardTM security
The integrity and security of JavaTM are widely recognized. The security management developed
for smart cards is implemented by the JCVM. The following features provide program and data
integrity and security from malicious programs:
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The Java CardTM language is provided by the class file verifier, which is made off-card,
before code is downloaded into the card.
JCRE security enforces firewalls to isolate applets, which prevents unauthorized access
of objects created by one applet from being used by another.
Java CardTM compilers provide extensive stringent error checking when the program is
compiled.
For example: all references to methods and variables are checked to make sure that the objects
are of the same type. The compiler also ensures that a program does not access any noninitialized
variables.
All accesses to methods and instance variables in a Java CardTM class file are through
access modifiers. These modifiers define a level of access control for each method. You
can declare a method to be public (no limitations) protected (accessible by methods in
the same subclass or package) or private (no access by other classes). If no declaration
is made, the default allows the method to be accessed by any class in the same
package.
Basic Java CardTM types and operations are well defined. All primitive types have a
specific size and all operations are performed in a designated order.
Malicious programs cannot forge pointers to memory because there are no pointers that
can be accessed by programmers or users.
Additionally Java CardTM accesses variables only through references to them from the
JavaTM stack. Malicious programs are prevented from "snooping" around in the Java
CardTM variable heap because the values of the local variables are unavailable after
every method invocation. A method cannot access resources it shouldn't.
2.3.3 Applet runtime environment
The Java CardTM technology defines a Java CardTM Runtime Environment (JCRE) that contains
the full runtime environment to support the execution of Java CardTM program. The JCRE
contains the Java Card Virtual Machine (JCVM) and provides classes and methods (API) to help
developers create applets.
2.3.4 Java CardTM Virtual Machine
The Java CardTM Virtual Machine (JCVM) is a version of the JavaTM Virtual Machine (JVM)
adapted for smart cards. It controls access to all smart card resources, such as memory and I/O
and allows applications to be securely loaded to the card post-issuance.
The JCVM executes the JavaTM byte code subset on the smart card, ultimately providing the
functions accessible from outside, such as signature, log-in and applications.
2.3.5 Java CardTM API
The available Application Programming Interface (API) classes allow developing applications and
provide system services to those applications. These classes define the conventions by which a
Java CardTM applet accesses the JCRE and native functions, including operating system
functionality, memory access, and I/O operations. The APIs used by the card contains four
packages:
javacard.framework - this package contains the basics features needed to work with
the Java CardTM card.
java.lang - this package contains all the exceptions corresponding to a misusage of
arrays, casts, and security. It is automatically imported by the compiler itself.
javacard.security - this package contains a framework for the cryptography functions
supported on the card.
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javacardx.crypto - this package contains a cipher class with encryption and decryption
capabilities.
2.3.6 3GPP TS 43.019 API
These API classes are an extension of the Java Card 2.1.1 API classes. They allow application
programmers accessing to the functions and data described in TS 51.011 and 3GPP 51.014,
such as the SIM based services can be quickly developed and loaded onto SIM cards. The APIs
used by the card contains two packages:
sim.access - this package provides the means to the applets for accessing to the GSM
data and file system of the GSM application defined in the TS 51.011 standard.
sim.toolkit - this package provides the means for the toolkit applets to register to the
events of the toolkit framework, to handle TLV information and to send proactive
command according to the 3GPP TS 51.014 specification.
2.3.7 JCRE support services
The Java CardTM applets do not directly receive the incoming messages. These are first
processed by the JCRE, which calls upon a method of the applet to process the APDU
commands. The JCRE supports services dedicated to smart cards.
It allows applet isolation thanks to applet firewall ensuring that no other applet may use,
access or modify the contents of an object owned by another applet, except as defined
by the applet itself.
It includes a way to share objects between applet object sharing. An applet may permit
restricted or unrestricted sharing of any of its objects. In another terms, any applet
cannot access the fields of or objects of another applets implemented. There is an
exception when the other applet explicitly provides interface for access.
It includes a way to manage atomic transactions. A transaction is a logical set of updates
of a persistent object. The transaction is atomic when all the fields are updated or none
are. The mechanism of an atomic transaction allows protection against events such as
power loss in the middle of the transaction, and against program errors that may cause
data corruption. If the transaction cannot complete, the card data are restored to their
pre-transaction states, at the exception of the content of the transient objects.
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2.4 Writing a Toolkit Applet
The Java CardTM technology allows applets written in the JavaTM language to be executed on a
smart card. It defines a Java CardTM Runtime Environment (JCRE) and provides classes and
methods to help developers create applets. In addition, the 3GPP TS 43.019 standard provides
classes and methods to create toolkit applets; that are applets triggered at the following of a
toolkit event selection.
2.4.1 Overview of a toolkit applet architecture
A toolkit applet class must extend from the javacard.framework.Applet class. This class is the
super class for all the applets residing on a Java CardTM. It defines the common methods an
applet must support in order to interact with the JCRE during its lifetime. The class Applet
provides a framework for applet execution. Methods defined in this class are called by the JCRE
when it receives APDU commands.
To be considered as a toolkit applet, a Java CardTM applet must implement:
The ToolkitInterface interface to be able to process toolkit events described in the TS
43.019 standard
The ToolkitConstants interface to have access to constants specified in 3GPP 51.014
standard (for example: tags of the TLV/BerTLV, General results...).
After the applet code has been properly loaded and linked with other packages on the card, the
appleťs life starts when an applet instance is created and registered with the JCRE's registry
table. A toolkit applet must implement the static method install() to create an applet instance. It
must also register the instance with the JCRE by invoking one of the two register() methods and
register the toolkit events by invoking the ToolkitRegistry() method.
On the card, a toolkit applet is in an inactive stage until it is explicitly triggered via an event.
Once the applet is triggered, the SIM toolkit framework calls the appleťs processToolkit()
method. This method processes the current toolkit event. If an error occurs, the throws() method
of the ToolkitException interface specifies the reason of the exception. Finally, the applet returns
in an inactive stage.
2.4.2 Example of applet
This applet has been designed to test the Call Control facility on a Mobile. It has one menu entry.
When the user selects this entry, the applet will display a menu asking the user if he wants to
activate the Call Control Facility (1) or De-activate it (2). If the user selects (1), the applet will
register to the EVENT_CALL_CONTROL_BY_SIM else it will not register to the later by calling
the clear method. If the facility is activated, when the user will set up a call, the applet will be
triggered and will modify its call (result = 02) providing a new number (NUMBER which is a
constant).
/*
* Copyright (c) Gemalto, unpublished
* work, created 2000. This computer program includes
* Confidential, Proprietary Information and is a Trade
* Secret of Gemalto Technology Corp. All use,
* disclosure, and/or reproduction is prohibited unless
* authorized in writing.
* All Rights Reserved.
*
*/
package CallControl;
import javacard.framework.*;
import sim.access.*;
import sim.toolkit.*;
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// You declare the class CallControl.
// This class inherits from the superclass Applet issued from
// the Java card library 2.1.1 and implements the methods
// defined in the interface ToolkitInterface and
// ToolkitConstants issued from TS 43.019.
public class CallControl extends Applet implements ToolkitInterface, ToolkitConstants {
private ToolkitRegistry reg;
private short menuId;
private static final short RES_CMD_PERF = (short)0;
// The number to be call: 06 17 86 85 17
private static final byte [] NUMBER_BY_CONTROL={(byte)0x81,(byte)0x60,(byte)0x71,
(byte)0x68,(byte)0x58, (byte)0x71};
private static final byte [] NUMBER_CALLED={(byte)0x81,(byte)0x10,(byte)0x74,
(byte)0x64,(byte)0x35,(byte)0x07};
private static final byte [] ALPHA_ID_1 = {(byte)'C',(byte)'a',(byte)'ľ,(byte)'ľ,
(byte)' ,(byte)'r',(byte)'e',(byte)'p', (byte)'ľ,(byte)'a',(byte)'c',(byte)'e',
(byte)'ď}
private static final byte [] ALPHA_ID_2 = {(byte)'A',(byte)'p',(byte)'p',(byte)'ľ,
(byte)'e',(byte)'ť};
private static final byte [] MENU_TITLE= {(byte)'C',(byte)'a',(byte)'ľ,(byte)'ľ,
(byte)' ',(byte)'C',(byte)'o',(byte)'n', (byte)'ť,(byte)'r',(byte)'o',(byte)'ľ};
private static final byte [] EXITING = {(byte)'E',(byte)'x',(byte)'i',(byte)'ť,
(byte)'i',(byte)'n', (byte)'g'};
private static final byte [] ACTIV = {(byte)'C',(byte)'a',(byte)'ľ,(byte)'ľ,(byte)' ',
(byte)'C',(byte)'o',(byte)'n',(byte)'ť, (byte)'r',(byte)'o',(byte)'ľ,(byte)'',
(byte)'a',(byte)'c',(byte)'ť,(byte)'i', (byte)'v',(byte)'a',(byte)'ť,(byte)'e',
(byte)'ď};
private static final byte [] ALREADY_ACTIV = {(byte)'C',(byte)'a',(byte)'ľ,(byte)'ľ,
(byte)' ',(byte)'C',(byte)'o',(byte)'n', (byte)'ť,(byte)'r',(byte)'o',(byte)'ľ,
(byte)' ',(byte)'a',(byte)'ľ,(byte)'r', (byte)'e',(byte)'a',(byte)'ď,(byte)'y',
(byte)' ',(byte)'a',(byte)'c',(byte)'ť, (byte)'i',(byte)'v',(byte)'a',(byte)'ť,
(byte)'e',(byte)'ď};
private static final byte [] DESACTIV = {(byte)'C',(byte)'a',(byte)'ľ,(byte)'ľ,
(byte)' ',(byte)'C',(byte)'o',(byte)'n', (byte)'ť,(byte)'r',byte)'o',(byte)'ľ,
(byte)' ',(byte)'Ď,(byte)'e',(byte)'-', (byte)'a',(byte)'c',(byte)'ť,(byte)'i',
(byte)'v',(byte)'a',(byte)'ť,(byte)'e', (byte)'ď};
private static final byte [] ERROR = {(byte)'E',(byte)'r',(byte)'r',(byte)'o',(byte)'r'};
private static final byte [] SELECT_ITEM = {(byte)'C',(byte)'a',(byte)'ľ,(byte)'ľ,
(byte)' ',(byte)'C',(byte)'o',(byte)'n', (byte)'ť,(byte)'r',(byte)'o',(byte)'ľ};
private static final byte [] ACTIVATE = {(byte)'A',(byte)'c',(byte)'ť,(byte)'i',
(byte)'v',(byte)'a',(byte)'ť,(byte)'e'};
private static final byte [] DEACTIVATE = {(byte)'Ď,(byte)'e',(byte)'s',(byte)'a',
(byte)'c',(byte)'ť,(byte)'i',(byte)'v', (byte)'a',(byte)'ť,(byte)'e'};
private static final byte [] SET_UP_CALL = {(byte)'S',(byte)'e',(byte)'ť,(byte)'u',
(byte)'p',(byte)' ',(byte)'C',(byte)'a', (byte)'ľ,(byte)'ľ};
private static final byte [] PROFILE =
{
(byte)0, // PROFILE DOWNLOAD
(byte)3, // MENU SELECTION
(byte)8, // COMMAND RESULT
(byte)9, // CALL CONTROL BY SIM
(byte)12, // HANDLING OF THE ALPHA ID
(byte)16, // DISPLAY TEXT
(byte)24, // SELECTED ITEM
(byte)28 // SET UP CALL
};
// Constructor of your applet: create an object of your class
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// The constructor role is double. First it must register
// the object, and second, it must define the menu
// selection. Here, only one menu item is created.
private CallControl(byte [] buffer, short offset, short length) {
// Register to the SIM Toolkit Framework
reg = ToolkitRegistry.getEntry();
// Define the menu entry
menuId = (short)((short)0x00FF & reg.initMenuEntry(MENU_TITLE, (short)0,
(short)MENU_TITLE.length, (byte)0, false, (byte)0, (short)0));
register();
}
// install method
// This method allows creating the instance file. It
// calls the constructor via the keyword: new.
public static void install(byte [] buffer, short offset, byte length)
{
new CallControl(buffer, offset, (short)(length & 0x00FF));
}
// process method
// This method (applet class) allows incoming APDU
// commands for a Java Card applet only.
public void process(APDU apdu)
{
}
// AT THIS STADE, THE APPLET IS COMPLETELY INSTALLED
// processToolkit method (from ToolkitInterface, GSM
// 03.19)
// A toolkit applet uses this method to process the
// current toolkit event.
public void processToolkit(byte event)
{
EnvelopeHandler eh;
EnvelopeResponseHandler erh;
ProactiveHandler ph;
ProactiveResponseHandler prh;
short res;
short i;
byte [] msg;
switch(event)
{
case EVENT_PROFILE_DOWNLOAD:
for(i=(short)0; i < (short)PROFILE.length ; i++}
{
if(!MEProfile.check(PROFILE[i]))
{
reg.disableMenuEntry((byte)menuId);
return;
}
}
reg.enableMenuEntry((byte)menuId);
return;
case EVENT_CALL_CONTROL_BY_SIM:
erh = EnvelopeResponseHandler.getTheHandler();
erh.appendTLV(TAG_ALPHA_IDENTIFIER, ALPHA_ID_1, (short)0,
(short)ALPHA_ID_1.length);
erh.appendTLV(TAG_ADDRESS, NUMBER_BY_CONTROL, (short)0,
(short)NUMBER_BY_CONTROL.length);
// Allowed with modification
erh.postAsBERTLV(SW1_RP_ACK, (byte)0x02);
return;
case EVENT_MENU_SELECTION:
ph = ProactiveHandler.getTheHandler();
ph.init(PRO_CMD_SELECT_ITEM, (byte)0, DEV_ID_ME);
ph.appendTLV((byte)(TAG_ALPHA_IDENTIFIER|TAG_SET_CR), SELECT_ITEM, (short)0,
(short)SELECT_ITEM.length);
ph.appendTLV(TAG_ITEM, (byte)1, ACTIVATE,(short)0, (short)ACTIVATE.length);
ph.appendTLV(TAG_ITEM, (byte)2, DEACTIVATE,(short)0, (short)DEACTIVATE.length);
ph.appendTLV(TAG_ITEM, (byte)3, SET_UP_CALL,(short)0,
(short)SET_UP_CALL.length);
res = (short)((short)0x00FF & ph.send());
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switch(res)
{
case RES_CMD_PERF:
prh = ProactiveResponseHandler.getTheHandler();
switch(prh.getItemIdentifier())
{
case (short)1:
if(!reg.isEventSet(EVENT_CALL_CONTROL_BY_SIM))
{
reg.setEvent(EVENT_CALL_CONTROL_BY_SIM);
msg = ACTIV;
}
else
{
msg = ALREADY_ACTIV;
}
break;
case (short)2: msg = DESACTIV;
reg.clearEvent(EVENT_CALL_CONTROL_BY_SIM);
break;
case (short)3: // Set Up Call
ph.init(PRO_CMD_SET_UP_CALL, (byte)0x00,
DEV_ID_NETWORK);
ph.appendTLV(TAG_ALPHA_IDENTIFIER, ALPHA_ID_2,
(short)0, (short)ALPHA_ID_2.length);
ph.appendTLV(TAG_ADDRESS, NUMBER_CALLED, (short)0,
(short)NUMBER_CALLED.length);
ph.send();
return;
default:
msg = ERROR;
break;
}
break;
default:
msg = EXITING;
break;
}
ph.initDisplayText((byte)0x80, DCS_8_BIT_DATA, msg, (short)0, (short)msg.length);
ph.send();
return;
}
}
}
2.4.3 Limitations in an applet creation
This part deals with some guidelines to increase the card resource memory. The following list is
not exhaustive. Keep in mind that you must always test several possibilities to optimize the
applet.
Do not use:
Unicode character support
32-bit and 64-bit integers
Float and double data types
Threads
Multidimensional arrays
Create one class only.
Create all objects in the appleťs constructor.
Clean up the code; that is, remove the methods, variables, operations that are not
necessary in the applet.
Factoring common code to eliminate redundancy in a method.
Use primitive types. Avoid creating objects from primitive types. Developing a class to
encapsulate primitive types can give more functionality than the primitive type itself, but it
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can use memory resource of the card.
Use constants, via the keywords static and final. Using static final improves both
application size and performance.
Avoid using local object or arrays. Each instance of an object or array declared with a
local scope allocates memory. As a Java Card does not have a garbage collection, this
memory is never freed. Each call to a local method allocates memory again, and soon or
later uses up the memory resources.
Re-use variable when possible because the more variables are used the more card
resources are consumed.
Use a variable to store an array element. Usually accessing array elements requires
more byte codes than accessing local variable. If an array element is accessed multiple
times from different locations in the same methods, save the array value in a local
variable on the first access, then use the variable in the subsequent accesses.
Gain on-card execution time by use transient objects to store intermediate results or
frequently updated temporary data. Writing to RAM is 1,000 times faster than writing in
EEPROM.
Use the switch statement in place of the if-else statement. It often executes faster and
takes less memory than the equivalent if-else.
Use compound arithmetic statements instead of separate assignments. The reason is
separate assignments require additional instructions to first store all intermediate values,
then load them back for the next calculation.
2.5 Developer Suite as a Java Card IDE
The development of Java Card Applets and STK Applets is greatly facilitated by the use of the
Developer Suite, a fully integrated Java Card IDE.
The Developer Suite ­ based on Eclipse Java IDE ­ will help you learn how to develop Java
Card Solutions with Rapid Application Development Wizards for basic Java Card and STK
Applets. The Suite also provides an End-to-end Simulation Environment, enabling complete
testing of your Solution before you deploy it in the Real World.
A free evaluation of the Developer Suite is available on the Gemalto Developer Network:
http://developer.gemalto.com.
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3 Basic Development Rules
Failure to conform to the set of recommendations in this chapter may lead to basic development
issues and lack of standard optimization.
D1 ­ Use APIs, rather than rewriting methods, whenever possible
Use APIs
Description :
Use APIs whenever it is available to avoid the need to duplicate the code. Moreover, the strongest
mechanism provided by the API shall always be chosen. This holds for Java Card standard API, GP
API and UICC API.
D2 ­ Coding and storing PINs and Keys in primitive arrays must be avoided
Coding PINs & Keys
Description :
To ensure security of the card is not compromised, coding / storing of PINs and KEYs must not be in
primitive arrays. Below are examples of GOOD recommended practice.
Example :
OwnerPIN pin;
Pin = new OwnerPIN (tryLimitApplet, maxPINSizeApplet);
Pin.update( pinApplet offset, length )
Key rsaPrivateKey;
rsaPrivateKey = (RSAPPrivateKey) KeyBuilder.buildKey
(KeyBuilder.TYPE_RSA_PRIVATE, KeyBuilder.LENGTH_RSA_512, False);
rsaPrivateKey.setExponent(bufferExp, offsetExp, lengthExp);
rsaPrivateKey.setModulus(bufferMod, offsetMod, lengthMod);
D3 ­ Sensitive data must be initialized at the beginning and clears at the end of the session
Sensitive data ­ initializations and clearing
Description :
Rule is applicable to global arrays, keys updates and Session Objects.
Always :
* Initialize at the beginning of the session
* And clear at the end of the session
Note :
To reset a key, always use the clearKey() method of the javacard.security.key interface. Do not
explicitly erase the key with zeros or other value.
Rationale:
Benefits from platform counter-measures.
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When using clearKey() method, the initialized state of the key is set to false.
Example :
sessionflags =
JCSystem.makeTransientByteArray
((short)13,JCSystem.CLEAR_ON_RESET);
sessionflags =
JCSystem.makeTransientByteArray
((short)13,JCSystem.CLEAR_ON_DESELECT);
sessionKey = (DESKey)KeyBuilder.buildKey(
KeyBuilder.TYPE_DES_TRANSIENT_RESET,
KeyBuilder.LENGTH_DES3_2KEY,
false);
sessionKey = (DESKey)KeyBuilder.buildKey(
KeyBuilder.TYPE_DES_TRANSIENT_DESELECT,
KeyBuilder.LENGTH_DES3_2KEY,
false);
The code in red will only reset the
data on RESET. As a result, data is
not cleared at the end of the select
session.
The code in green shows you the
correct setting
D4 ­ Sensitive data must be stored in transient data
Sensitive data ­ Storage
Description :
Store your session data in transient data. Avoid using the APDU buffer to store this data.
Example :
sessionflags =
JCSystem.makeTransientByteArray
((short)13,JCSystem.CLEAR_ON_DESELECT);
Store your sensitive data in
transient data.
D5 ­Protect your sensitive data against Rollback attack
Counter management to combat against Rollback attack
Description :
An attacker can use the fact that your code is under transaction, and power off the card in order to
roll-back to the old value. Counter management must be implemented to counter Rollback attacks
when working with sensitive data.
Rule:
If a sensitive mechanism that relies on a ratification counter needs to be managed, always perform
the following actions:Check
the ratification counter value and return error if set to 0.
Atomically decrement the ratification counter
Verify that the code is not under transaction
Run the "try" function
If the "try" is successful, atomically increment the ratification counter.
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D6 - All initialized buffers (containing menu item, strings...) must be declared as static
Initialized buffers declared as static
Description :
All initialized buffers (containing menu item, strings...) must be declared as static:
* to save execution time during installation
* to save code space
to prevent errors during installation (transaction buffer full)
Example :
public class exampleD1 extends Applet
implements ToolkitInterface{
byte[] menu1 = {(byte)'m', (byte)'e',
(byte)'n', (byte)'u', (byte)'1' };
static byte[] menu2 = {(byte)'m', (byte)'e',
(byte)'n', (byte)'u', (byte)'2' };
For all initialized arrays, avoid the
declaration in red, even if the syntax
correct. Use the syntax in green
instead.
D7 - Reentrance
Description:
A proactive session, initiated by an APPLICATION A, execution is interrupted when a second
APPLICATION B (can be the same one) is activated.
After APPLICATION B has been finished, and no additional event occurs before the terminal
response is received, control is returned to APPLICATION A, so that its own execution can be
finished.
A terminal CAN only manage one proactive command at a given time, it is not possible for the
Application B to initiate a proactive session.
If this application uses the ETSI 102 241 UICC API (Release 6) or the 3GPP 43.019 API (Release 5),
a ToolkitException with the reason code HANDLER_NOT_AVAILABLE will be thrown when trying to
retrieve the ProactiveHandler system instance.
How to deal with re-entrance?
* Requiring an SMS-Submit
Can be used only: if the application has to send proactive commands only when triggered by
EVENT_FORMATTED_SMS_PP_ENV.
The remote server must require a response packet using SMS-Submit when sending a message
to the application (the card shall implement the 3GPP 43.019 Rel-5)
Advantages:
o it is a standard mechanism
o there is no need to implement anything related to this mechanism in the application
* Throwing an ISOException
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This Release-6 solution is quite simple: the applet directly throws an ISOException with reason
code '93 00' if it is not able to process the current message.
It may be very useful if there is no issues with formatted SMS and counter check, and could be
used for instance on ENVELOPE (Timer Expiration), as the message will be sent at a later stage
by the terminal.
* Event Proactive Handler Available
Simplest solution for the applet developer, as it does not have to check ProactiveHandler
availability when triggered by this event.
If an applet is not able to process a first incoming message linked to the unavailability of
ProactiveHandler, it has to do as follows:
1. Save needed data
2. Register the applet on EVENT_PROACTIVE_HANDLER_AVAILABLE
3. Exit.
When the applet is triggered on this event, it is sure that ProactiveHandler is available, and saved
data can be processed.
This method is applicable on Release-6 cards
D8 ­ Handler availability
Description :
A minimum requirement for the availability of the system handlers and the lifetime of their
contents are defined. Please refer to 3GPP 31130 ((U)SIM API), or TS 101476 (GSM API).
Example :
public class exampleD6 extends Applet
implements ToolkitInterface{
byte[] apduBuffer;
void processToolkit(byte event){
EnvelopeHandler hdlr;
switch (event) {
case PROFILE_DOWNLOAD:
hdlr = EnvelopeHandler.getTheHandler();
default:
break;
}
The assignment in red is forbidden
since the EnvelopeHandler is not
available by the system during the
profile download procedure.
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D9 ­ Global and local variables
Global vs local variables
Description:
There are several types of variables in Java Card applet:
* Instance variables (global variables): created at the object instantiation.
* Local variables: they are accessible only from the function or block in which they are
declared.
Some basic rules:
* Not use instance variable when a static variable can be used. It permits avoiding
redundancies in class instances.
* Minimize the number of instance variables.
* Declare your constants as static final. (code size and performance optimization)
o Static variables which are pre-defined in code and are not expected to change during
the application life-time should be changed to "static final"
o Arrays containing pre-defined values (like menu items, text messages, strings...) must
be declared as static to optimize both the applet installation processing time and the
EEPROM occupation
* Do not declare too much arguments in a method very costly in memory (RAM),
* Local variables access are faster than global variable access
o Working variables (like loop counters, temporary storage variables...) must be
declared as local variables of a method instead of global variables of a class, to avoid
over-stressing the EEPROM
o Working buffers must be declared as transient arrays (located in RAM) whenever
possible, to avoid over-stressing the EEPROM. If not possible (lack of RAM
resources), care must be taken on the working buffers update frequency (when and
how many times)
o RAM space should be used only when needed, as RAM is a costly resource. 5 bytes
per kilo byte of used EEPROM seems a relevant ratio for cost efficiency.
* Factorize arguments of a method Use instance variables instead of parameters and
Pass an object instead of a list of parameters
* Maximize the local variables used however reuse them as much as possible
The consequence of these recommendations is the reduction of the execution time.
General advantage:
Reducing the number and size of classes and objects facilitates the resolution of a bug easier
readability.
Example :
public class MyApplet{
private byte OFFSET_A = (byte) 1;
private byte OFFSET_B = (byte) 2;
...
Static declaration: variable value
may change over time
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}
public class MyApplet{
private static byte OFFSET_A = (byte) 1;
private static byte OFFSET_B = (byte) 2;
...
}
public class MyApplet{
private byte OFFSET_A = (byte) 1;
private byte OFFSET_B = (byte) 2;
...
}
public class MyApplet{
private static final byte OFFSET_A =
(byte) 1;
private static final byte OFFSET_B =
(byte) 2;
...
}
Constant declaration: variable
value will never change over time
void init_my_buffer(byte[] buffer, short
length){
short offset = (short)(length/2);
Util.arrayCopyNonAtomic(buffer, 0, data_1,
offset,(short)8);
offset = (short)( length/2+8);
Util.arrayCopyNonAtomic(buffer, 0, data_2,
offset,(short)8);
offset =(short)(length/2+16);
Util.arrayCopyNonAtomic(buffer, 0, data_3,
offset,(short)16);
}
Reuse local variable
http://developer.gemalto.com 31/50
D10 ­ Storage of references to temporary entry point objects is forbidden
Temporary entry point objects reference storage
Description :
The Java CardTM standard specifies JCRE entry point objects (EPO). Among those EPOs the
temporary EPO are prevented to be stored in class variables, instance variables or array components.
The JCRE detects and restricts attempts to store references to these objects as part of the applet
firewall functionality. A Security Exception is thrown by the system in that case.
Examples of main Temporary EPO
* APDU
* EnvelopeHandler, ProactiveHandler, EnvelopeResponseHandler,
ProactiveResponseHandler.
Example :
public class exampleD8 extends Applet implements
ToolkitInterface {
byte[] apduBuffer;
byte[] envHandler;
void process(APDU apdu){
byte[] buffer;
apduBuffer = apdu.getBuffer();
buffer = apdu.getBuffer();
}
The assignment in red is
forbidden by the system since it is
an attempt to store the APDU
buffer reference to an instance
variable.
The assignment in green is
correct, since the storage is on a
local reference, so released at the
end of the process() method
execution.
void processToolkit(byte event){
byte[] handler;
envHandler = EnvelopeHandler.getTheHandler();
handler = EnvelopeHandler.getTheHandler();
}
Same for the handlers: the
assignment in red is forbidden by
the system since it is an attempt
to store the Envelope handler
reference to an instance variable.
The assignment in green is
correct, since the storage is on a
local reference, so released at the
end of the processToolkit()
method execution.
D11 ­ Keep methods sizes small
Keep methods sizes small
Description:
Size of methods should be small. A maximum of about 300 bytes for one method is acceptable. It is
recommended to break-up into more methods.
General advantage:
Having smaller methods improves readability and ease maintenance and debugging.
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D12 ­ Ensure number of methods do not exceed 256 methods per class
Ensure methods do not exceed 256 methods per class
Description:
When breaking up the methods, take care not to produce too many methods, because there is a
limitation of 256 methods per class and secondly more methods will mean a bigger constant pool
component, which will be completely moved to EEPROM when patching.
http://developer.gemalto.com 33/50
4 Recommendations to minimize risks in field
Due to the limited lifespan of the EEPROM and flash memory, applets that perform excessive
read/writes repeatedly on the same location has the risk of stress failure in the field. This section
covers the recommendations for in the applet design to minimize the need for read/write for a memory
location.
Failure to abide to the recommendations in this chapter may lead to a severe field issue: the card can
become mute or with unexpected behavior.
F1 - Check where all your variables are stored and accordingly move them if there is a risk of
NVM stress (guaranteed 100,000 updates for E
2
PROM and FLASH technologies)
Stress EEPROM : objects in EEPROM risk
Description :
The Java and Java Card memory models are different: on a Java Card, objects are allocated in
EEPROM. It means:
* all global variables of basic type (byte, short...)
* objects (created using the Java new instruction)
will be located in EEPROM.
The only memory chunks allocated in RAM are:
* the local variables,
* the parameters of methods
the transient objects explicitly created by using dedicated Javacard.framework.APIs
Example :
public class exampleF1 extends Applet {
byte counter=0;
byte[] workingBuffer;
byte[] transientBuffer;
short i, j, k;
private ToolkitRegistry reg;
counter, workingBuffer, transientBuffer,
i, j, k are global variables of basic types
located in EEPROM
reg is an object of type ToolkitRegistry
located in EEPROM
void process(APDU apdu){
short i, j, k;
byte[] reference;
...
}
apdu is a parameter of process method
located in RAM
i, j, k, reference are local variables of
basic type located in RAM
public exampleF1 () {
transientBuffer =
JCSystem.makeTransientByteArray((short)10
0, JCSystem.CLEAR_ON_RESET);
workingBuffer = new byte[12];
}
...
}
workingBuffer is a global variable
located in EEPROM, referencing an
object located also in EEPROM created
with new.
transientBuffer is a global variable
located in EEPROM, referencing a
transient array located in RAM, created
using dedicated Java CardTM APIs.
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F2 - Avoid writing in EEPROM upon STATUS event reception
Event status
Description :
An applet registered on the STATUS event will be triggered each time the handset issues a STATUS
APDU command, i.e. every 1 or 2 minutes. Special care must be taken in the applet on the EEPROM
parts (object fields, files...) that are written during that procedure.
Example :
public class exampleF2 extends Applet
implements ToolkitInterface{
byte[] workingBuffer;
byte[] transientBuffer;
short s;
public exampleF2() {
transientBuffer =
JCSystem.makeTransientByteArray((short)20
0, JCSystem.CLEAR_ON_RESET);
workingBuffer = new byte[200];
}
void processToolkit(byte event){
short i;
switch (event) {
case EVENT_STATUS_COMMAND:
for (s=0; s<200; s++) {
workingBuffer[s]=(byte)s;
}
default:
break;
}
This routine in red is called every time a STATUS
command is sent by the handset, ie every 1 or 2
minutes)
The routine fills up the buffer referenced
by workingBuffer located in EEPROM.
Furthermore the index s used in the for
loop is also located in EEPROM.
This routine potentially writes 200 in
EEPROM on two EEPROM cells every
2 minutes, ie 144000 times a day
The EEPROM will be then killed in
a few days.
void processToolkit(byte event){
short i;
switch (event) {
case EVENT_STATUS_COMMAND:
for (i=0; i<200; i++) {
transientBuffer[i]=(byte)i;
}
default:
break;
}
This routine in green is called every time a
STATUS command is sent by the handset, ie
every 1 or 2 minutes)
The routine fills up the buffer referenced
by transientBuffer, which is located in
RAM.
Furthermore the index i used in the for
loop is a local variable so located in
RAM.
This routine gives exactly the same
result as the routine in red but does not
write in EEPROM in any case.
Note : standard 102.241 release 6 defines a standard buffer in RAM accessible for applets (available
in uicc.system.UICCPlatform, retrievable using getTheVolatileByteArray()). This buffer can be used
as a temporary buffer in case the applet developer needs a temporary RAM space.
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F3 - Avoid writing in EEPROM upon file update events when the concerned file is a HIGH
update activity file
File Update
Description :
Same remark as for rule #2 above for the event FILE_UPDATE, some files (EFLoci, EFBCCH for
instance) are defined in the 3GPP51.011 & 3GPP31.102 standard with a HIGH update activity. If an
applet is triggered on such file update, care must be taken in the applet on the other EEPROM parts
(object fields, files) that are written during that procedure.
Example :
Same example as in F2
Consider EVENT_FILE_UPDATE instead of EVENT_STATUS_COMMAND
F4.1 - Avoid passing too many parameters in a function (4 or 5 max)
F4.2 - Avoid declaring too many local variables inside each method
F4.3 - Reduce the overall nesting level (ie a function calling a function). Latest Gemalto Java
cards allow more than 20 nesting levels
Warning functions calls / Jstack
Description :
A Java Card stores all methods parameters and local variables in a RAM dedicated area called the J-
Stack.
On a Smartcard, the RAM resources are limited.
Example :
F4.1 Passing too many parameters
void myMethod( byte [] buf1
short off1
short len1
byte [] buf2
short off2
short len2
byte [] buf3
short off3
short len3
)
9 parameters declared + this (current
object reference).
try to reduce the number of
parameters passed in a method
F4.2 Declaring too many local variables
void myMethod ( byte [] buf1
short off1
short len1)
)
short s1, s2, s3;
byte b1, b2, b3;
byte[] ba1, ba2;
Object o1, o2;
10 local variables declared
try to optimize the local variable
usage in methods (reuse variable for
several purpose for example)
F4.3 Nesting level
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void myMethod1(byte [] buf1
short off1
short len1)
) {
myMethod2();
}
void myMethod2() {
myMethod3();
}
void myMethod3() {
myMethod4();
}
void myMethod4() {
doSomething();
}
void doSomething() {
...
}
When calling myMethod1, the nesting
level is 5 since mymethod1 invokes
myMethod2() which invokes
myMethod3() which invokes
myMethod4() which invokes
doSomething().
Each method invocation creates
information in the J- Stack, the J-Stack
size in RAM being limited, so special
care must be taken on the nesting level
of the overall application.
F5 - ALL objects making up the application are created during installation
Objects creation
Description :
As opposed to Java, a Java Card does not necessarily implement a Garbage collector running in
background for freeing the memory space taken by no longer referenced objects. Thus it is
recommended to create all new objects at applet installation time (i.e. in the install() method or
constructor).
Example :
public class exampleF5 extends Applet {
byte[] workingBuffer;
void process(APDU apdu){
workingBuffer = new byte[12];
...
}
}
Object assigned to workingBuffer is
created in process(): an object will
then be created AT EACH APDU
SENT TO THE APPLET, so filling up
the remaining free NVM.
public exampleF1 () {
workingBuffer = new byte[12];
...
}
Object assigned to workingBuffer is
created in the appleťs constructor: the
object will then be created only once
at applet installation time
This way is recommended
Use the constructor or the appleťs
install() method.
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F6 - If your application uses the Java Card transactions:
* The transaction critical section (ie part between a Begin and a Commit) shall be as small as
possible.
* The begin and commit shall be done in the same method.
* All execution paths of a method starting a transaction shall complete it.
* The transaction critical section shall be protected by a try-catch block
Transactions (ex : Begin and Abort management with exception, ...)
Description :
This section aims at preventing card tear out or power supply loss during an application execution.
See examples in the related "development guidelines for anti-tearing"
F7 - Insert a MORE TIME proactive command if your toolkit process is longer than 2s in order
not to block the handset
Verification that the execution time is < 2s : More Time / Trig applet
Description :
The SCP102.221 standard specifies that a long Card Application Toolkit process may prevent the
handset from sending "normal GSM commands" which are time critical (authentication...), and
therefore advises the application to send MORE TIME proactive commands not to block the handset.
The applet developer must highlight in his application the processes longer than 2 sec. and must then
accordingly insert MORE TIME proactive commands whenever required.
Example :
public class exampleF7 extends Applet
implements ToolkitInterface{
byte[] transientBuffer;
public exampleF2() {
transientBuffer =
JCSystem.makeTransientByteArray((short)10
0, JCSystem.CLEAR_ON_RESET);
}
void processToolkit(byte event){
switch (event) {
case EVENT_MENU_SELECTION:
for (short s=0; s<200; s++) {
doSomeProcessing();
}
default:
break;
}
The following routine will execute upon
menu selection, the method
doSomeProcessing() 200 times, thus
is likely to take a long time to execute,
thus exceeding 2 seconds.
void processToolkit(byte event){
ProactiveHandler proh;
switch (event) {
case EVENT_MENU_SELECTION:
for (short s=0; s<200; s++) {
doSomeProcessing();
if ((short)(s%(short)50) == (short)0)
{
proh =
The green routine allows sending a
MORE_TIME proactive command every 50 loop-
rounds.
http://developer.gemalto.com 38/50
ProactiveHandler.getTheHandler;
proh.init((byte)PRO_CMD_MORE_TIME,
(byte)0x00, DEV_ID_ME);
proh.send();
}
}
default:
break;
}
Note for the example: in Release 6, a standard method initMoreTime()has been integrated.
F8 - In reentrance, take into account that the OS resources are limited: proactive handlers,
available RAM.
Toolkit applications must be tested in reentreance, ie when a CAT context is already active.
Working in reentrance
Description :
Re-entrance refers to the case whereby a proactive session (initiated by an application A) execution is
interrupted when a second application B (which can be the same one) is activated. The nested
application B (in other words, the application triggered while another application is already activated)
has its own file and access conditions context. After application B has been finished, and no additional
event occurs before the terminal response is received, control is returned to the first application, so
that its own execution can be finished.
In that re-entrance case, the handlers may not be available to the application, so a related exception
will be thrown. It will impose the application to manage properly that exception, meaning have a trycatch
section to correctly process the application when handlers are not available.
Example :
public class exampleF8 extends Applet implements
ToolkitInterface, ToolkitConstants {
static byte[] text = {(byte)'ť, (byte)'e',
(byte)'x', (byte)'ť};
void processToolkit(byte event) {
ProactiveHandler proh;
switch (event) {
case EVENT_MENU_SELECTION:
try {
proh = ProactiveHandler.getTheHandler();
proh.initDisplayText((byte)0x80,
DCS_8_BIT_DATA, text, (short) 0,
(short) text.length) ;
proh.send() ;
}
catch (ToolkitException te) {
if (te.getReason() ==
ToolkitException.HANDLER_NOT_AVAILABLE) {
}
// process reentrance mngt here
...
}
The proactive handler is
retrieved in a try-catch clause,
thus in case of reentrance, the
handler may not be available,
and the code in the catch
clause will then be executed.
Note: the test of the exception
reason is a reinforcement to be
sure of the exception type.
Depending of the application,
this test may be useless.
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default:
break;
}
}
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5 Anti-Tearing recommendations
5.1 Reminder on anti-tearing mechanism
The anti-tearing mechanism aims at ensuring correct card integrity and consistency when the card is
pulled out of its terminal or after power loss. The card execution is in that case unexpectedly
interrupted. The anti-tearing mechanism ensures the detection of such interruptions and the recovery
operations during the next card session.
The Java CardTM memory model is based on objects stored by default in persistent memory. Several
mechanisms are provided to ensure data integrity and consistency.
5.1.1 Atomicity on objects' field updating
Because objects are stored in NVM, the update of an object field requires several ms. and there is a
potential risk of power loss during this operation. If this happen, the content of the object field would
be unpredictable.
To solve that issue, the Java Card Virtual Machine specification mandates that object field update is
atomic: either entirely performed or not.
This is enforced by the Virtual Machine that automatically detects the update of objects stored in
NVM and uses the backup mechanism to perform the update.
Note that, for optimization purposes, it is possible to use RAM cache. In such case, only the cache
flush performs the NVM update and uses the backup mechanism.
5.1.2 Transaction services
In some cases (examples given below), it is necessary to perform several memory updates
consecutively but the data integrity relies on the fact that these fields are all updated or not.
The Java Card specification defines a "Transaction System" to solve that issue:
* APIs are provided to Applications in order to start, commit or abort a transaction (see detail
below)
* A transaction can be started in an APDU command but shall be completed before the end of this
command
* If not completed, the system automatically aborts the ongoing transaction before processing the
next command
* Only a single transaction can be started at a time.
The Java Card API specification defines the following services:
* Begin transaction: starts a new transaction. All the following persistent memory updates are
subject to rollback
* Commit transaction: ends the ongoing transaction: all pending memory update are definitively
performed
* Abort transaction: cancel all persistent memory updates
5.1.3 Embedded services using transaction services
The card platform itself, the embedded applications and the embedded services are also subject to
use transaction services.
Examples (non exhaustive list) where transaction services are used:
http://developer.gemalto.com 41/50
* Allocation of an object may require several update that can not be performed partially without
consequences on the entire system integrity
* Application linking and installation requires several memory update that shall be entirely
performed to ensure consistency
* Updating a PIN code implies the update of several internal fields requiring consistency
* ...
Depending on the layer using the transaction services, it is possible to use either the Java Card API or
to use the underlying native (and proprietary) API.
5.1.4 By-passing the on-going transaction may be necessary
In some circumstances, it may be necessary to by-pass the on-going transaction. Examples:
* It shall not be possible to rollback to the previous value of the ratification counter of a PIN
code if its verification failed
* Even if a transaction is in progress, it may be useful to update a large amount of data (i.e an
array) without the need to roll-back to its initial value
* The fields update of objects created during the installation of an application does not
necessarily require to take part to the on-going transaction because, in case of abortion, the
objects will also be discarded
* ...
This can be done either using the Java Card API for byte arrays (arrayCopyNonAtomic) or using
underlying and proprietary native services.
5.2 Architecture overview
Summarizing, the anti-tearing mechanism is split into different architecture layers.
Application
Application
backup
Java Card Runtime Environment
Card Operating System
atomicity
transaction
system
Application(U)SIM
...
5.2.1 Level 1 ­ Backup module
At the lowest level, the backup module, provided by the card operating system, offers services to copy
NVM areas from the Heap to a dedicated and secured stack. This module provides standard
transaction services: begin, commit and rollback. It is the core engine of the transaction system and
follows a specific development process (separated specification and design with re-use in all Gemplus
http://developer.gemalto.com 42/50
platforms, specific unitary test plan and campaigns, dedicated code-reading procedures and specific
security audit).
In some cases, its implementation is adapted in order to take into account NVM characteristics and
chip security features. As examples, it may include specific redundancy checksums on backup data,
can implement a cyclic transaction stack in order to reduce NVM stress on some pages.
5.2.2 Level 2 ­ Atomicity and transaction services provided by Java Card
The upper layers do not directly use the backup module. It is encapsulated, as described before, by
* The "atomicity services" directly implemented in the Virtual Machine interpreter
* The "transaction system" accessible via a Java Card API
5.2.3 Level 3 ­ Use of transaction services by applications
Finally, if the use of atomicity services is implicitly done by applications (each time an object field is
updated), the use of the transaction system requires explicit calls to the API whenever required.
The following recommendations give advices and examples on when to use these services.
5.3 Guidelines to protect applications against card tear-out
5.3.1 Optimization of transaction critical section
The transaction critical section is the part of the code included between the calls to
JCSystem.beginTransaction() and JCSystem.commitTransaction().
T1 ­ The transaction critical section shall be as small as possible
* Rationale
This rule is standard for critical sections. Both the time and the number of resources
implicated in a critical section shall be minimized. For transactions, the aim is to
significantly reduce the number of potential errors and also because, by construction,
the sequence protected by the transaction is sensitive for the system integrity and
consequently for its security and reliability.
* Example
It is necessary to avoid non-necessary calls to other objecťs virtual method because
there is no control on the side effects like overflow of the transaction buffer, unexpected
exception, ... The entire reliability may be broken if the method is overwritten later.
// WRONG !!
void performDebit(short amount, short dbtID) {
...
JCSystem.beginTransaction();
if( (amount <= this.amount) && isKnownID(dbtID) ){
this.amount -= amout;
this.lastDebitID = dbtID;
}
JCSystem.commitTransaction();
}
// CORRECT
void performDebit(short amount, short dbtID) {
http://developer.gemalto.com 43/50
...
if( (amount <= this.amount) && isKnownID(dbtID) ){
JCSystem.beginTransaction();
this.amount -= amout;
this.lastDebitID = dbtID;
JCSystem.commitTransaction();
}
...
}
T2 ­ The begin and commit transaction shall be done in the same method
* Rationale
This recommendation is the first necessary step (even if not sufficient) to avoid providing
APIs that leave the system with a potential non-committed transaction.
This design constraint either helps to write small critical sections, helps for code-reading
(and audit), and helps to provide strong, scalable and reusable classes.
T3 ­ All the execution paths of a method starting a transaction shall complete it.
* Rationale
When a transaction is started, all the execution paths shall be studied and shall
complete or abort the transaction. This covers conditional jumps but also exception
handling.
5.3.2 Protection of transaction critical section
T4 ­ The transaction critical section shall be protected by a try-catch block
* Rationale
Several exceptions may occur. The first one to take into account is the one thrown if a
transaction is already in progress (remind that a single transaction can be started at a
time).
Then, a transaction stack overflow that may occur if the transaction buffer of the
underlying platform is not large enough to keep a copy of all modified objects' fields.
Finally, other exception may also be thrown by methods called within the transaction
and shall be handled (see previous recommendation).
* Example
void performDebit(short amount, short dbtID) {
if( (amount <= this.amount) && isKnownID(dbtID) ){
try {
JCSystem.beginTransaction();
this.amount -= amout; // may throw a
TransactionException
this.lastDebitID = dbtID; // may throw a
TransactionException
updateLOGfile(amount,dbtID); // may throw a UserException
JCSystem.commitTransaction();
}
catch (TransactionException te){
Critical section
http://developer.gemalto.com 44/50
JCSystem.abortTransaction();
this.nbErrors++;
}
catch (UserException ue){
JCSystem.abortTransaction();
this.nbWarning++;
}
}
5.3.3 Protecting objects' allocations
T5 ­ Allocate object under transaction
* Rationale
Most of the allocations are performed during the application installation, which is
automatically protected by a transaction started by the system before calling the install
method.
However, if you need to allocate object later in the code, there is a potential memory
leak on cards that does not embed a Garbage Collector.
class myApplet extends Applet {
myObject myField;
process(...){
...
myField = new myObject();
...
}
}
In this example, the object allocation is performed first (execution of byte-code `new'),
then the execution of the object constructor is executed, and finally the storage of its
reference into myField is performed.
If a card tear out occurs between the object allocation and the field assignment, the
memory allocated by the object will be lost until the application is deleted or the
Garbage Collector executed.
The time between the new and the field assignment of the applet is not negligible, even
though the developer has the feeling to immediately perform the assignment when
writing the Java code.
* Example
class myApplet extends Applet {
myObject myField;
process(...){
...
JCSystem.beginTransaction();
myField = new myObject();
JCSystem.commitTransaction();
...
}
}
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* Exception
If the application targets cards embedding a Garbage Collector (available since Java
CardTM 2.2), it is not absolutely necessary to apply this recommendation because the
unreachable object will be automatically collected.
http://developer.gemalto.com 46/50
5.4 Recommendations for specific and proprietary APIs
5.4.1 Protecting the use of `object de-allocation'
T6 ­ De-allocate objects under transaction
* Rationale
Object de-allocation is provided by a proprietary API and is dedicated for very specific
purposes. Each time possible, the use of interoperable Garbage Collector shall be
done instead of using this method.
Using this method is symmetrical to allocation and requires the same caution.
void process(...){
...
if ((myBuffer != null) && (newSize > oldSize)) {
Gsystem.deAllocate(myBuffer);
MyBuffer = new byte[newSize];
}
}
If a tear out occurs between the buffer de-allocation and the new buffer creation, the
buffer is marked by the system as free whereas the application has kept a reference on
that free buffer resulting in a dangling pointer.
In that case, the critical section is made of the de-allocation and the allocation of the
new buffer.
* Example
void process(...){
...
if ((myBuffer != null) && (newSize > oldSize)) {
try {
JCSystem.beginTransaction();
Gsystem.deAllocate(myBuffer);
MyBuffer = new byte[newSize];
JCSystem.commitTransaction();
}
catch (TransactionException te) {
if(te.getReason() == TRANSACTION_BUFFER_FULL )
JCSystem.abortTransaction();
}
}
}
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6 Application development Checklist
Type Title Description Check
F1 - stress
E2PROM :
objects in
E2PROM
F1 - Check where all your variables are stored and
accordingly move them if there is a risk of NVM
stress (guaranteed 100,000 updates for E
2
PROM
and FLASH technologies)
F2 ­ event
status
F2 - Avoid writing in EEPROM upon STATUS event
F3 - file update F3 - Avoid writing in EEPROM upon file update
events when the concerned file is a HIGH update
activity file
F4 - Warning
functions calls /
Jstack
F4.1 - Avoid passing too many parameters in a
function (4 or 5 max)
F4.2 - Avoid declaring too many local variables
inside each method
F4.3 - Reduce the overall nesting level (ie a function
calling a function). Latest Gemalto Java cards allow
more than 20 nesting levels.
F5 - Objects
creation (card
with garbage
collector or
objects are
created at install
only)
F5 - ALL objects making up the application are
created during installation.
F6 Transactions
(ex
: Begin and
Abort mngt with
exception, ...)
F6 - If your application uses the Java Card
transactions:
* The transaction critical section (ie part between
a Begin and a Commit) shall be as small as
possible.
* The begin and commit shall be done in the
same method.
* All execution paths of a method starting a
transaction shall complete it.
* The transaction critical section shall be
protected by a try-catch block
Minimizing field
issue risks
F7 - Verification
that the
execution time is
< 2s : More
Time / Trig
F7 - Insert a MORE TIME proactive command if
your toolkit process is longer than 2s in order not to
block the handset
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applet
F8 - Working in
reentrance
F8 - In re-entrance, take into account that the OS
resources are limited : proactive handlers, available
RAM.
Toolkit applications must be tested in re-entrance, ie
when a CAT context is already active.
D1 ­ Use APIs Use APIs, rather than rewriting methods, whenever
possible
D2 ­ Coding
PINs & Keys
Coding and storing PINs and Keys in primitive
arrays must be avoided
D3 ­ Sensitive
data initializations
&
clearing
Sensitive data must be initialized at the beginning
and clears at the end of the session
D4 ­ Sensitive
data - Storage
Store your session data in transient data. Avoid
using the APDU buffer to store these data
D5 - Protect
your sensitive
data against
Rollback attack
Counter management must be implemented to
combat against Rollback attacks when working with
sensitive data.
D6 - Initialized
buffers declared
as static
All initialized buffers (containing menu item,
strings...) must be declared as static:
D7 - reentrance How to deal with re-entrance?
* Requiring an SMS-Submit
* Throwing an ISOException
* Event Proactive Handler Available
D8 - handlers
availability
See example above
D9- Global vs
local variables
Check if you use the right variable type:
* Instance variables (global variables):
created at the object instantiation.
* Local variables: they are accessible only
from the function or block in which it is
declared.
Development
basics
D10 - Storage of
references to
temporary entry
point objects is
the storage of references should be done throw a
local reference
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forbidden
D11 ­ Keep
methods sizes
small
Break down complex methods into smaller methods
D12 ­ Ensure
methods do not
exceed 256
methods per
class
Ensure that number of methods per class do not
exceeded 256
T1 ­ The
transaction
critical section
shall be as small
as possible
Time and no of resources in critical section are to be
kept to the minimum possible
T2 ­ The begin
and commit
transaction shall
be done in the
same method
Check that the begin and commit transaction is
within the same method
T3 ­ All the
execution paths
of a method
starting a
transaction shall
complete it.
Check that all execution paths are completed or
aborted. This should include error or exception
handling routines
T4 ­ The
transaction
critical section
shall be
protected by a
try-catch block
To prevent transaction stack overflow during an
exception, the transaction critical section must be
protected using a try-catch block
T5 ­ Allocate
object under
transaction
If objects are allocated later in the code and not
during application installation, check that your object
creation is done within transaction.
If Garbage collector is activated (available since
Java CardTM 2.2), this is not mandatory.
Anti Tearing
T6 ­ De-allocate
objects under
transaction
Deallocate objects method is used only when a tear
out is detected by the method. For all other time,
the use of interoperable Garbage Collector shall be
done instead of using this method
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END OF DOCUMENT