Assignment - feedback
Zdeněk Říha
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Assignments
l
1.Write a program (in any programming language) that will prepare a padded block for RSA signature
with PKCS#1 v1.5 padding. Input is a file and RSA key size; output is the padded octet string
(print it in hex). Use SHA-256 as the hash function. Do not use crypto library for the padding
itself [5 points].
2.Write a program that will generate 2048 bit DH parameters in DER format. Use any cryptolibrary
and any programming language. Recommendation: Openssl & C & functions DH_new,
DH_generate_parameters_ex, i2d_DHparams_bio. [5 points].
l
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Assignment 1
lPKCS#1 v1.5 padding
lWe open the PKCS#1 v2.2 document :-)
lAlso available as RFC 8017
lWe find the relevant section
l9.2 EMSA-PKCS1-v1_5
lEMSA-PKCS1-v1_5-ENCODE (M, emLen)
lInput: Message + length of padded result (key size)
lOutput: EM (the padded results) to be signed
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Assignment 1
lAs we can see in step 5 the result is:
l
l
lwhere PS is composed of 0xff bytes to fit the size
land T is DER encoded structure containing the hash algorithm and hash itself:
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Assignment 1
lThe authors of PKCS#1 are very nice and provide a help for common hash algorithms
l
l
l
l
lwhere H is the hash (32 bytes for SHA-256)
lPrint the EM in hex
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Example - result
l0001
fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
ffffffff
00
3031300d060960864801650304020105000420
7f5effba4da0fc825aa799e9bb3e4c50aec930e34f26e37f75a58fd3e26b0a38
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Example - python
lSubmitted by Oldrich Florian
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Assignment 2
lRead all PKCS#3 standard
l8 pages including introduction, history, …
lAssignment:
lWrite a program that will generate 2048 bit DH parameters in DER format.
l
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Assignment 2
lProgramming language
lUse any cryptolibrary and any programming language.
lRecommendation: Openssl & C & functions DH_new, DH_generate_parameters_ex, i2d_DHparams_bio
lTry “man dh”
lVerify results:
l“openssl asn1parse -inform DER -in yourfile.der”
l“openssl dhparam -inform DER -in yourfile.der -noout -text”
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Sample code in C
lBased on submission of Roman Chrenst
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Viewing the result
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