数字证书编码ASN.1

ASN.1描述与实例

1．TBSCertificate 的 ASN.1描述与实例

TBSCertificate格式用ASN.1描述如下:
TBSCertificate :=SEQUENCE {
version
[0] EXPLICIT Version DEFAULT v1,
serialNumber
CertificateSerialNumber,
signature
Algorithmldentifier,
issuer
Name,
validity
Validity,
subject
Name,
subjectPublicKeyInfo SubjectPublicKeyInfo,
issuerUniqueID[1] IMPLICIT Uniqueldentifier OPTIONAL,
-- If present, version MUST be v2 or v3

subjectUniqueID [2] IMPLICIT Uniqueldentifier OPTIONAL,
-- If present, version MUST be v2 or v3
extensions[3]EXPLICIT Extensions OPTIONAL
-- If present, version MUST be v3
}
Extensions ::=SEQUENCE SIZE (1..MAX) OF ExtensionTBSCertificate 中各项内容具体值如表13-3所示。

TBSCertificate	值
version	02
serialNumber	04 96
signature	sha 1 WithRSAEncryption ( 1.2.840.113549.1.1.5)
issuer	“CN=Virtual CA,C=CN”
validity	notBefore=20200222000000、notAfter=20220222000000
subject	“CN=chenshaoqing，OU=Person，C=CN”
subjectPublicKeyInfo	空
issuerUniquelD subjectUniquelD	空
extensions	包含6个扩展项（Extension ): basicContraints、subjectKeyldentifier、keyUsage、extKeyUsage,netscapeCertType、authorityKeyIdentifier

2.Extension的ASN.1描述与实例Extension格式用ASN.1描述如下:

Extension :=SEQUENCE {
extnID
OBJECT IDENTIFIER,
critical
BOOLEAN DEFAULT FALSE,
extnValue
OCTET STRING }
Extension各扩展项值如表13-4所示。

3.Certificate 的ASN.1描述与实例Certificate格式用ASN.1描述如下:

Certificate ::=SEQUENCE {
tbsCertificate
TBSCertificate,
signatureAlgorithm
AlgorithmIdentifier,
signature Value
BIT STRING }
Certificate中各项内容的具体值如表13-5所示。

四、DER编码过程

（一）对Extension进行DER编码

各扩展项具体内容用ASN.1描述如下:
BasicConstraints ::=SEQUENCE{
cA
BOOLEAN DEFAULT FALSE,
pathLenConstraint
INTEGER (O..MAX)OPTIONAL}
SubjectKeyIdentifier ::= Keyldentifier
(KeyIdentifier ::= OCTET STRING)KeyUsage ::= BIT STRING
ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX)OF KeyPurposeld

(KeyPurposeld ::= OBJECT IDENTIFIER)NetscapeCertType ::= BIT STRING
AuthorityKeyldentifier ::=SEQUENCE{
keyIdentifier
[O] KeyIdentifier
OPTIONAL,
authorityCertIssuer
[1]GeneralNames
OPTIONAL,
authorityCertSerialNumber [2] CertificateSerialNumber OPTIONAL }(KeyIdentifier ::= OCTET STRING)
Extension为 SEQUENCE结构类型，不同扩展项DER编码值包含在OCTET STRING类型extnValue中，编码规则采用结构类型定长模式。各扩展项DER编码值用括号分隔。其中，对于BIT STRING类型，编码后第1个字节表示填充位数或未使用位数。