Certificate  ::=  SEQUENCE  {
     tbsCertificate       TBSCertificate,
     signatureAlgorithm   AlgorithmIdentifier,
     signatureValue       BIT STRING  }
TBSCertificate  ::=  SEQUENCE  {
     version         [0]  EXPLICIT Version DEFAULT v1,
     serialNumber         CertificateSerialNumber,
     signature            AlgorithmIdentifier,
     issuer               Name,
     validity             Validity,
     subject              Name,
     subjectPublicKeyInfo SubjectPublicKeyInfo,
     issuerUniqueID  [1]  IMPLICIT UniqueIdentifier OPTIONAL,
                          -- If present, version shall be v2 or v3
     subjectUniqueID [2]  IMPLICIT UniqueIdentifier OPTIONAL,
                          -- If present, version shall be v2 or v3
     extensions      [3]  EXPLICIT Extensions OPTIONAL
                          -- If present, version shall be v3
     }
Version  ::=  INTEGER  {  v1(0), v2(1), v3(2)  }
CertificateSerialNumber  ::=  INTEGER
AlgorithmIdentifier  ::=  SEQUENCE  {
     algorithm               OBJECT IDENTIFIER,
     parameters              ANY DEFINED BY algorithm OPTIONAL  }
Name ::= CHOICE {
  RDNSequence }
RDNSequence ::= SEQUENCE OF RelativeDistinguishedName
RelativeDistinguishedName ::=
  SET OF AttributeTypeAndValue
AttributeTypeAndValue ::= SEQUENCE {
  type     AttributeType,
  value    AttributeValue }
AttributeType ::= OBJECT IDENTIFIER
AttributeValue ::= ANY DEFINED BY AttributeType
Validity ::= SEQUENCE {
     notBefore      Time,
     notAfter       Time }
Time ::= CHOICE {
     utcTime        UTCTime,
     generalTime    GeneralizedTime }
UniqueIdentifier  ::=  BIT STRING
SubjectPublicKeyInfo  ::=  SEQUENCE  {
     algorithm            AlgorithmIdentifier,
     subjectPublicKey     BIT STRING  }
Extensions  ::=  SEQUENCE SIZE (1..MAX) OF Extension
Extension  ::=  SEQUENCE  {
     extnID      OBJECT IDENTIFIER,
     critical    BOOLEAN DEFAULT FALSE,
     extnValue   OCTET STRING  }

Figure 2: The ASN.1 definition of a certificate.