ASN.1 Type System

The concept of a data type is fundamental to the Abstract Syntax Notation One (ASN.1) standard. Every field of a certificate request structure is associated with a type. Consider, for example, the PKCS #10 ASN.1 certificate syntax shown in the following example.

 

 

--------------------------------------------------------------------
-- PKCS #10 Certificate request.
--------------------------------------------------------------------
CertificationRequestInfo ::= SEQUENCE 
{
   version                 CertificationRequestInfoVersion,
   subject                 Name,
   subjectPublicKeyInfo    SubjectPublicKeyInfo,
   attributes              [0] IMPLICIT Attributes
}

-------------------------------------------------------
-- Version number.
-------------------------------------------------------
CertificationRequestInfoVersion ::= INTEGER

-------------------------------------------------------
-- Subject distinguished name (DN).
-------------------------------------------------------
Name ::= SEQUENCE OF RelativeDistinguishedName

RelativeDistinguishedName ::= SET OF AttributeTypeValue

AttributeTypeValue ::= SEQUENCE 
{
   type               OBJECT IDENTIFIER,
   value              ANY 
}

-------------------------------------------------------
-- Public key information.
-------------------------------------------------------
SubjectPublicKeyInfo ::= SEQUENCE 
{
   algorithm           AlgorithmIdentifier,
   subjectPublicKey    BITSTRING
}

AlgorithmIdentifier ::= SEQUENCE 
{
  algorithm           OBJECT IDENTIFIER,
  parameters          ANY OPTIONAL    
} 

-------------------------------------------------------
-- Attributes.
-------------------------------------------------------
Attributes ::= SET OF Attribute

Attribute ::= SEQUENCE 
{
   type               OBJECT IDENTIFIER,
   values             AttributeSetValue
}

AttributeSetValue ::= SET OF ANY

The high-level request structure, CertificationRequestInfo, is a type that is made up from a sequence of other types. When a type is or contains only basic types, string types, or ANY, it cannot be broken down further. For example, the version field is a CertificationRequestInfoVersion type which is, in turn, an INTEGER type, a basic ASN.1 type that is not composed from other types.

A type system enables the syntax of a request to be presented visually in a manner readily understood by developers, and it enables the request to be consistently encoded for transmission across a network. For more information about encoding, see Distinguished Encoding Rules. For more information about ASN.1 types, see the following topics.

Topic	Description
Basic Types	Discusses the following data types: BIT STRING BOOLEAN INTEGER NULL OBJECT IDENTIFIER OCTET STRING
String Types	Discusses the following string types: BMPString IA5String PrintableString TeletexString UTF8String
Constructed Types	Discusses ASN.1 data types that can contain basic types, string types, or other constructed types.