数字证书格式编码

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
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。

DER编码过程
1．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。

2．对TBSCertificate进行DER编码
TBSCertificate内容编码规则采用结构类型定长模式，具体编码过程如表13-7所示。

1、序列号=1174（0x0496）

echo -n -e "xA0x03x02x01x02x02x02x04x96x30x0Dx06x09x2Ax86x48x86xF7x0Dx01x01x05x05x00" > 20181217.der

2、证书签发者 DN="CN=Virtual CA

echo -n -e "x30x22x31x0Bx30x09x06x03x55x04x06x13x02x43x4Ex31x13x30x11x06x03x55x04x03x13x0Ax56x69x72x74x75x61x6Cx20x43x41" >> 20181217.der

3、证书有效期=20200222000000-20220222000000

echo -n -e "x17x0Dx32x30x32x30x30x32x32x32x30x30x30x30x5Ax17x0Dx32x30x32x32x30x32x32x32x30x30x30x30x5A" >> 20181217.der

4、证书持有者DN=CN=你的名字拼音， OU=Person

echo -n -e "x30x37x31x0bx30x09x06x03x55x04x06x13x02x43x4ex31x11x30x0fx06x03x55x04x0ax13x08x32x30x31x38x31x32x31x37x31x15x30x13x06x03x55x04x03x13x0cx63x68x65x6Ex73x68x61x6Fx71x69x6ex67x20" >> 20181217.der