ASN.1:
Cryptographic files
Zdeněk Říha

ASN.1 Grammar
lTo understand the structure (what is the meaning of particular fields) we need ASN.1 grammar
l

ASN.1 – RSA keys
Source:
PKCS#1
< RSA.key

ASN.1 – RSA padding
lPKCS#1 v1.5
lm = 0x00 || 0x01 || 0xFF … 0xFF || 0x00 || T
lWhere T is defined as DER encoding of
l
l
lIn practice:
Source:
PKCS#1

ASN.1 – RSA signature
lRSA signature is the number s = md mod n
< TSA.crt

ASN.1 – signature OIDs
Source:
BSI TR-03105 Part 5.1

ASN.1 – RSA PSS params
RSASSA-PSS
SHA256
SHA256
MGF1
Source:
PKCS#1
< CSCA_CZE.crt

ASN.1 – DSA keys
DSAPrivateKey is an INTEGER, usually denoted as X
Source:
RFC 5480
Source:
OpenSSL
< DSA.key

ASN.1 – DSA signature
Source:
RFC 5480
< DSA.crt

ASN.1 – DSA - OIDs
Source: RFC 5480


ASN.1 – ECDSA keys
ECPoint
INTEGER
Source: RFC 5915

ASN.1 - ECDSA public key
< CSCA_Switzerland.crt


ASN.1 – ECDSA signatures
1.2.840.10045.4.1 - ecdsa-with-SHA1
Source:
RFC 5480
< CSCA_Switzerland.crt

ASN.1 – ECDSA signature OID
Source:
BSI TR-03105 Part 5.1

ASN.1 - certificates
Source:
RFC 5280

ASN.1 – certificates - pubkey
Source:
RFC 5280
< CSCA_CZE.crt

ASN.1 – certificates - times
lUntil 2049: UTCTime
lYYMMDDHHMMSSZ
lFrom 2050: GeneralizedTime
lYYYYMMDDHHMMSSZ
Source:
RFC 5280
< CSCA_CZE.crt

ASN.1 – certificates - names
Source:
RFC 5280

ASN.1 – certificate - names
< CSCA_CZE.crt


ASN.1 – certificate - names
Source:
ITU-T X.520

ASN.1 – certificate - names
Source:
ITU-T X.520

Certificate profiles
lFor particular areas/purposes there exist certificate profiles which prescribe what kind of
attributes will be used in Names
lE.g. for electronic passports ICAO Doc. 9303 states:
Source:
ICAO Doc. 9303

ASN.1 – certificates – v3
lCritical x non-critical extensions
Source:
RFC 5280

ASN.1 – certs – extensions
< CSCA_CZE.crt


X509v3 cert extensions
lAuthority Key Identifier
lIdentification of the issuing CA
lNon critical
lSimilarly “Subject Key Identifier”
Source:
RFC 5280

X509v3 cert extensions
lKey Usage
lRestrictions of the use of the key
Source:
RFC 5280

X509v3 cert extensions
lExtended Key Usage
lPurposes of the certified key
Source:
RFC 5280

X509v3 cert extensions
lCertificate Policies
lPolicy relevant for the issue and use of the certificate
lPreferably only an OID
Source:
RFC 5280

X509v3 cert extensions
lSubject Alternative Name
lIssuer Alternative Name
l“Internet style identities”
lEmail
lDNS name
lIP address
lURL
lMust be verified by CA

X509v3 cert extensions
lBasic Constraints
lIs Subject a CA?
lMax. length/depth of the certificate chain/path
lA pathLenConstraint of zero indicates that no non-self-issued intermediate CA certificates may
follow in a valid certification path.
Source:
RFC 5280

X509v3 cert extensions
lName Constraints
lOnly for CA certificates
l“indicates a name space within which all subject names in subsequent certificates in a
certification path MUST be located”
l
Source:
RFC 5280

X509v3 cert extensions
lPolicy Constraints
lMust be critical
lFor CA certificates
lConstraints path validation
lProhibit policy mapping (or)
lRequire acceptable policy OID in each certificate
Source:
RFC 5280

X509v3 cert extensions
lCRL Distribution Points
lHow to obtain CRL
l
Source:
RFC 5280

ASN.1 – certificate request
Source:
RFC 5280

ASN.1 - CRL
Source:
RFC 5280

ASN.1 – PKCS#7 / CMS
Source:
RFC 5652

ASN.1 - PKCS#7 / CMS
Source:
RFC 5652

PKCS#7 Sample
< France.p7s


ASN.1 – PKCS#8
Source:
PKCS#8