x509解析

X509

X509的ASN.1定义

[Certificate ::= SEQUENCE {
	tbsCertificate TBSCertificate,
	signatureAlgorithm AlgorithmIdentifier,
	signature BIT STRING
}

首先，一张x509证书最顶层包含三个东西。

• TBSCertificate是X509里最重要的主体，也就是证书内容。
• AlgorithmIdentifier记录的是该证书被CA所签的算法。
• BIT STRING记录的是CA对该证书的签名。

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 must be v2or v3
	subjectUniqueID [2] IMPLICIT UniqueIdentifier OPTIONAL,-- If present, version must be v2or v3
	extensions [3] EXPLICIT Extensions OPTIONAL-- If present, version must be v3
}

那TBSCertificate中包含了以上的字段：

• Version：证书版本号
• CertificateSerialNumber：证书序列号
• AlgorithmIdentifier：证书中签名的算法
• issuer Name：发布者的名字，即签名者
• validity Validity：证书的有效期，包含起始时间和过期时间
• subject Name：主体名字，即被签名者
• subjectPublicKeyInfo SubjectPublicKeyInfo：签名算法的公钥信息
• issuerUniqueID: 发布者的唯一序列号
• subjectUniqueID：被签者的唯一序号
• extensions：签名扩展内容，不知道用来干啥

Version ::= INTEGER {
	v1(0), v2(1), v3(2)
}

版本号字段就三种选项，V1, V2, V3

CertificateSerialNumber ::= INTEGER

版本序列号是一个整形变量

Validity ::= SEQUENCE {
	notBefore CertificateValidityDate,
	notAfter CertificateValidityDate
}

CertificateValidityDate ::= CHOICE {
	utcTime UTCTime,
	generalTime GeneralizedTime
}

证书有效时间包含证书的起始时间notBefore 和证书的过期时间notAfter

UniqueIdentifier ::= BIT STRING
	SubjectPublicKeyInfo ::= SEQUENCE {
	algorithm AlgorithmIdentifier,
	subjectPublicKey 
}

证书公钥信息包含两部分

• AlgorithmIdentifier签名算法
• 签名内容本身subjectPublicKey

Extensions ::= SEQUENCE OF Extension
Extension ::= SEQUENCE {
	extnID OBJECT IDENTIFIER,
	critical BOOLEAN DEFAULT FALSE,
	extnValue OCTET STRING
}

扩展不知道用来干啥

实际X509证书长什么样

先上传一个X509证书，来实际分析一下X509证书。这里第一种是ASN.1的二进制格式cert.der，第二种是openssl的PEM格式cert.pem。PEM格式的证书可以直接用文本编辑器看，而ASN.1格式的证书需要用asn1dump来查看。

cert.pem和cert.der下载
提取码：s36x

PEM格式

Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number: 826366320 (0x31415970)
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: CN=SRK1_sha256_1024_65537_v3_ca
        Validity
            Not Before: Jun 27 11:46:11 2018 GMT
            Not After : Jun 25 11:46:11 2026 GMT
        Subject: CN=IMG1_1_sha256_1024_65537_v3_usr
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (1024 bit)
                Modulus:
                    00:a9:9f:5e:de:64:b8:28:30:be:37:07:e3:ef:f4:
                    05:83:8f:96:b0:f2:60:76:13:60:61:84:e6:06:b0:
                    f7:fb:6d:8e:cb:cd:41:6b:21:60:7a:94:46:7c:99:
                    d8:e9:d6:31:01:a9:fc:36:88:b4:9e:85:58:40:d1:
                    33:0c:55:95:ba:bd:a5:30:a5:1f:ba:a0:d0:62:a1:
                    48:4c:83:e0:75:b2:51:55:11:b6:27:1f:8a:1c:d8:
                    80:15:0f:ab:c7:4a:37:e6:31:7f:43:dd:c0:4d:ed:
                    60:eb:88:a3:6d:9b:0c:c9:fa:96:57:97:71:48:65:
                    9c:70:e3:4e:d2:be:14:8d:8b
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Basic Constraints: 
                CA:FALSE
            Netscape Comment: 
                OpenSSL Generated Certificate
            X509v3 Subject Key Identifier: 
                6B:5D:F5:7E:3D:73:AE:49:6E:C7:E1:98:11:96:7E:D1:43:48:F1:00
            X509v3 Authority Key Identifier: 
                keyid:A3:41:D3:85:05:17:C0:90:1F:BE:AD:C1:50:04:E5:1C:01:79:6F:D2

    Signature Algorithm: sha256WithRSAEncryption
         9a:47:77:4b:ce:f8:0d:f3:e1:68:64:52:3e:9b:95:76:e7:cd:
         9f:35:c7:eb:73:eb:f2:6d:6e:2d:db:a3:51:e3:1f:98:12:2a:
         92:ff:58:b9:1c:39:a1:79:27:c1:80:76:cb:09:0a:35:e2:5f:
         ca:55:37:b7:9d:03:5a:09:8d:df:e6:34:4b:77:fe:47:0c:45:
         1c:27:60:bf:47:44:ba:3c:33:c1:5f:05:0b:0f:44:ec:16:33:
         1e:75:96:26:cb:5d:2f:1a:c9:d4:f2:4d:12:84:f8:1e:91:3f:
         de:07:3c:9f:71:8c:07:e0:a4:89:e2:f4:f0:e5:7c:8a:c5:9b:
         11:bf
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

在-----BEGIN CERTIFICATE-----上面是一段可以人肉读的描述文字，主要描述了TBSCertificate这个结构，可以看出它的版本号是x509v3， 序列号是826366320

    Data:
        Version: 3 (0x2)
        Serial Number: 826366320 (0x31415970)

签名算法是sha256WithRSAEncryption

   Signature Algorithm: sha256WithRSAEncryption

发布者是SRK1_sha256_1024_65537_v3_ca，被签者是IMG1_1_sha256_1024_65537_v3_usr

       Issuer: CN=SRK1_sha256_1024_65537_v3_ca
       Subject: CN=IMG1_1_sha256_1024_65537_v3_usr

有效期是从2018-6-27到2026-6-25

        Validity
            Not Before: Jun 27 11:46:11 2018 GMT
            Not After : Jun 25 11:46:11 2026 GMT

公钥是RSA 1024bit，公钥的moduls和exponent都列出来了：

            Public Key Algorithm: rsaEncryption
                Public-Key: (1024 bit)
                Modulus:
                    00:a9:9f:5e:de:64:b8:28:30:be:37:07:e3:ef:f4:
                    05:83:8f:96:b0:f2:60:76:13:60:61:84:e6:06:b0:
                    f7:fb:6d:8e:cb:cd:41:6b:21:60:7a:94:46:7c:99:
                    d8:e9:d6:31:01:a9:fc:36:88:b4:9e:85:58:40:d1:
                    33:0c:55:95:ba:bd:a5:30:a5:1f:ba:a0:d0:62:a1:
                    48:4c:83:e0:75:b2:51:55:11:b6:27:1f:8a:1c:d8:
                    80:15:0f:ab:c7:4a:37:e6:31:7f:43:dd:c0:4d:ed:
                    60:eb:88:a3:6d:9b:0c:c9:fa:96:57:97:71:48:65:
                    9c:70:e3:4e:d2:be:14:8d:8b
                Exponent: 65537 (0x10001)

接下来是扩展项和签名本身：

    Signature Algorithm: sha256WithRSAEncryption
         9a:47:77:4b:ce:f8:0d:f3:e1:68:64:52:3e:9b:95:76:e7:cd:
         9f:35:c7:eb:73:eb:f2:6d:6e:2d:db:a3:51:e3:1f:98:12:2a:
         92:ff:58:b9:1c:39:a1:79:27:c1:80:76:cb:09:0a:35:e2:5f:
         ca:55:37:b7:9d:03:5a:09:8d:df:e6:34:4b:77:fe:47:0c:45:
         1c:27:60:bf:47:44:ba:3c:33:c1:5f:05:0b:0f:44:ec:16:33:
         1e:75:96:26:cb:5d:2f:1a:c9:d4:f2:4d:12:84:f8:1e:91:3f:
         de:07:3c:9f:71:8c:07:e0:a4:89:e2:f4:f0:e5:7c:8a:c5:9b:
         11:bf

-----BEGIN CERTIFICATE-----到-----END CERTIFICATE-----存放的是整个证书的BASE64编码。用BASE64解码后就可以得到ASN.1编码的证书。 下面来看下解析ASN.1 格式的证书。

ASN.1格式

用ASN1DUMP打开cert.der, 可以看到根据这个二进制文件解析出了一颗树状结构体。这棵树的结构就跟Certificate ::= SEQUENCE定义是一模一样的。接下来我们一个个看看每一个ASN1条目中的东西，其中的内容跟pem格式文件里的内容可以一一对应上。

version

version 是一个ASN1 INTEGER类型(0x02)，长度是1(0x1), 数据是0x2，说明版本号是x509v3。

CertificateSerialNumber

序列号也是一个ASN1 INTEGER类型，长度是4， 数据是0x31415970就是826366320。

AlgorithmIdentifier

在www.oid-info.com上查询这个OID的结果，它代表的是sha256-with-rsa-signature，即使用了SHA1摘要算法的RSA签名算法。

issuer

issuer由一个sequence组成，sequence下面有一个set，set下面又跟了一个sequence。最后的sequence包含了两个东西，一个是OID，解析出来是commonName，另外一个UTF8String是issuer的名字，这里就是SRK1_sha256_1024_65537_v3_ca。

subject Name

subject由一个sequence组成，sequence下面有一个set，set下面又跟了一个sequence。最后的sequence包含了两个东西，一个是OID，解析出来是commonName，另外一个UTF8String是issuer的名字，这里就IMG1_1_sha256_1024_65537_v3_ca。

Subject Public Key Info

接下来是Subject Public Key Info，首先oid是rsaEncryption

Subject Public Key Info中的BIT STRING就是公钥的二进制，包含Modulus和Exponent，可以看到其内容和PEM里面存放的key是一样

CA对该证书的签名

证书的最后一段放的就是签名内容

python 解析x509证书

#!/usr/bin/python
import OpenSSL
import time
from dateutil import parser

def main():
    x509_cert_file = open('IMG1_1_sha256_1024_65537_v3_usr_crt.pem')
    x509_cert_payload = x509_cert_file.read()
    x509_cert_file.close()

    x509_cert = OpenSSL.crypto.load_certificate(OpenSSL.crypto.FILETYPE_PEM, x509_cert_payload)

    print('verison:{}'.format(x509_cert.get_version() + 1))
    print('serial_number:{}'.format(x509_cert.get_serial_number()))
    print('algorithm:{}'.format(x509_cert.get_signature_algorithm().decode("UTF-8")))
    print('issuer:.{}'.format(x509_cert.get_issuer().commonName))

    datetime_struct = parser.parse(x509_cert.get_notBefore().decode("UTF-8"))
    print('not before:{}'.format(datetime_struct.strftime('%Y-%m-%d %H:%M:%S')))

    datetime_struct = parser.parse(x509_cert.get_notAfter().decode("UTF-8"))
    print('not after:{}'.format(datetime_struct.strftime('%Y-%m-%d %H:%M:%S')))

    print('is_expired:{}'.format(x509_cert.has_expired()))
    print('public key:{}'.format(OpenSSL.crypto.dump_publickey(OpenSSL.crypto.FILETYPE_PEM, x509_cert.get_pubkey()).decode("utf-8")))


main()

运行结果

:~/my_scripts$./openssl_x509.py
verison:3
serial_number:826366320
algorithm:sha256WithRSAEncryption
issuer:.SRK1_sha256_1024_65537_v3_ca
not before:2018-06-27 11:46:11
not after:2026-06-25 11:46:11
is_expired:False
public key:-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCpn17eZLgoML43B+Pv9AWDj5aw
8mB2E2BhhOYGsPf7bY7LzUFrIWB6lEZ8mdjp1jEBqfw2iLSehVhA0TMMVZW6vaUw
pR+6oNBioUhMg+B1slFVEbYnH4oc2IAVD6vHSjfmMX9D3cBN7WDriKNtmwzJ+pZX
l3FIZZxw407SvhSNiwIDAQAB
-----END PUBLIC KEY-----

C语言解析X509证书

#include <openssl/x509.h>

int main()
{
    X509 *x509_cert;
    FILE *fp;
    unsigned char buf[5000], *p;
    int len, ret;
    BIO *b;

    fp = fopen("cert.der", "rb");
    if (!fp)
        return -1;

    len = fread(buf, 1, 5000, fp);
    fclose(fp);

    p = buf;
    x509_cert = X509_new();
    d2i_X509(&x509_cert, (const unsigned char **)&p, len);

    b = BIO_new(BIO_s_file());
    BIO_set_fp(b, stdout, BIO_NOCLOSE);
    ret =X509_print(b, x509_cert);

    BIO_free(b);
    X509_free(x509_cert);

    return 0;
}

运行结果

gcc openssl_x509.c -lcrypto -lssl;./a.out
Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number: 826366320 (0x31415970)
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: CN=SRK1_sha256_1024_65537_v3_ca
        Validity
            Not Before: Jun 27 11:46:11 2018 GMT
            Not After : Jun 25 11:46:11 2026 GMT
        Subject: CN=IMG1_1_sha256_1024_65537_v3_usr
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (1024 bit)
                Modulus:
                    00:a9:9f:5e:de:64:b8:28:30:be:37:07:e3:ef:f4:
                    05:83:8f:96:b0:f2:60:76:13:60:61:84:e6:06:b0:
                    f7:fb:6d:8e:cb:cd:41:6b:21:60:7a:94:46:7c:99:
                    d8:e9:d6:31:01:a9:fc:36:88:b4:9e:85:58:40:d1:
                    33:0c:55:95:ba:bd:a5:30:a5:1f:ba:a0:d0:62:a1:
                    48:4c:83:e0:75:b2:51:55:11:b6:27:1f:8a:1c:d8:
                    80:15:0f:ab:c7:4a:37:e6:31:7f:43:dd:c0:4d:ed:
                    60:eb:88:a3:6d:9b:0c:c9:fa:96:57:97:71:48:65:
                    9c:70:e3:4e:d2:be:14:8d:8b
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Basic Constraints:
                CA:FALSE
            Netscape Comment:
                OpenSSL Generated Certificate
            X509v3 Subject Key Identifier:
                6B:5D:F5:7E:3D:73:AE:49:6E:C7:E1:98:11:96:7E:D1:43:48:F1:00
            X509v3 Authority Key Identifier:
                keyid:A3:41:D3:85:05:17:C0:90:1F:BE:AD:C1:50:04:E5:1C:01:79:6F:D2

    Signature Algorithm: sha256WithRSAEncryption
         9a:47:77:4b:ce:f8:0d:f3:e1:68:64:52:3e:9b:95:76:e7:cd:
         9f:35:c7:eb:73:eb:f2:6d:6e:2d:db:a3:51:e3:1f:98:12:2a:
         92:ff:58:b9:1c:39:a1:79:27:c1:80:76:cb:09:0a:35:e2:5f:
         ca:55:37:b7:9d:03:5a:09:8d:df:e6:34:4b:77:fe:47:0c:45:
         1c:27:60:bf:47:44:ba:3c:33:c1:5f:05:0b:0f:44:ec:16:33:
         1e:75:96:26:cb:5d:2f:1a:c9:d4:f2:4d:12:84:f8:1e:91:3f:
         de:07:3c:9f:71:8c:07:e0:a4:89:e2:f4:f0:e5:7c:8a:c5:9b:
         11:bf