PKI、TLS、证书概念整理

4-minute read
Security
安全

1. PKI

Public Key Infrastructure - 公钥基础设施，这个名字，直译出来总觉得少点味，尤其是对于非安全领域，在接触到这个概念时，第一感觉它只是个“设施”，主要是用来管理“公钥”的，让人非常的疑惑。这类专有名词为什么不能稍微意译一下呢？

PKI是一个体系，一个架构，一系列东西的集合，这个集合中规定了各种元素，元素的作用，元素和元素之间的通讯协议等等。在这个集合所构成的体系之下，能够保证集合中的两个节点的通讯是安全的。而我们广袤的互联网所使用的PKI，就是一种基于可信第三方（CA，Certificate Authority）的PKI。下文所说的PKI如无特殊说明，就是指基于可信第三方的PKI。

2. HTTP over TLS

https_handshake

HTTPS的交互过程网络上资料很多，不再做赘述。比较令我好奇的是，当进行双向校验时，客户端如何选择证书？

在一个TLS建链过程中，有两个角色，一个客户端（client）主动发起，一个服务端（server）。

服务端必须有秘钥对（证书+私钥）。用于认证以及用于对称秘钥加密。如果服务端不校验客户端，同时客户端也不校验服务端证书，那客户端可以不配置任何证书相关的东西。如果服务端需要校验客户端，则需要有CA，用来验证客户端证书是否为其签发。当客户端配置的方式为keystore时，其中可能存在许多对秘钥对，客户端如何选择用哪个密钥对来通信呢？从协议交互图中看出来，有一个5过程，该过程为服务端要求客户端提供证书。

该博客中记录了TLS中，Certificate Request的内容 ：https://blog.csdn.net/mrpre/article/details/77868263

3. 证书(X509)、秘钥对

  • X.509，证书标准，定义证书格式，遵循ASN.1规范。X.509定义的证书结构：

    • Version Number，版本

    • Serial Number，序列号

    • Signature Algorithm ID，签名算法ID

    • Issuer Name，颁发者

    • Validity period，有效期

      • Not Before
      • Not After

    • Subject name，使用者

    • Subject Public Key Info，公钥信息

      • Public Key Algorithm
      • Subject Public Key

    • Issuer Unique Identifier (optional)，颁发者唯一ID

    • Subject Unique Identifier (optional)，使用者唯一ID

    • Extensions (optional)，扩展字段

      • …

    • Certificate Signature Algorithm，证书签名算法

    • Certificate Signature，证书签名

    #使用openssl查看一张证书，此证书选自jdk中默认证书中的一张
openssl x509 -text -in actalisauthenticationrootca.cer -noout

    Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number: 6271844772424770508 (0x570a119742c4e3cc)
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: C=IT, L=Milan, O=Actalis S.p.A./03358520967, CN=Actalis Authentication Root CA
        Validity
            Not Before: Sep 22 11:22:02 2011 GMT
            Not After : Sep 22 11:22:02 2030 GMT
        Subject: C=IT, L=Milan, O=Actalis S.p.A./03358520967, CN=Actalis Authentication Root CA
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (4096 bit)
                Modulus:
                    00:a7:c6:c4:a5:29:a4:2c:ef:e5:18:c5:b0:50:a3:
                  ...省略
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Subject Key Identifier:
                52:D8:88:3A:C8:9F:78:66:ED:89:F3:7B:38:70:94:C9:02:02:36:D0
            X509v3 Basic Constraints: critical
                CA:TRUE
            X509v3 Authority Key Identifier:
                keyid:52:D8:88:3A:C8:9F:78:66:ED:89:F3:7B:38:70:94:C9:02:02:36:D0
  
            X509v3 Key Usage: critical
                Certificate Sign, CRL Sign
    Signature Algorithm: sha256WithRSAEncryption
         0b:7b:72:87:c0:60:a6:49:4c:88:58:e6:1d:88:f7:14:64:48:
         ...省略

  • 证书类型：

    • DV，domain validated，域名验证，网站一般都使用DV
    • OV，organization validated，组织验证
    • EV，extended validated，扩展验证

  • 秘钥对，证书+私钥

4. Practice

JDK/JRE默认证书路径，这就是个jks文件：

$JAVA_HOME/lib/security/cacerts

确认某个站点发送了证书：

openssl s_client -showcerts -connect shareif.cn:443

~/Projects ᐅ openssl s_client -showcerts -connect shareif.cn:443
CONNECTED(00000005)
depth=2 C = US, O = DigiCert Inc, OU = www.digicert.com, CN = DigiCert High Assurance EV Root CA
verify return:1
depth=1 C = US, O = DigiCert Inc, OU = www.digicert.com, CN = DigiCert SHA2 High Assurance Server CA
verify return:1
depth=0 C = US, ST = California, L = San Francisco, O = "GitHub, Inc.", CN = www.github.com
verify return:1
---
Certificate chain
 0 s:/C=US/ST=California/L=San Francisco/O=GitHub, Inc./CN=www.github.com
   i:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 High Assurance Server CA
-----BEGIN CERTIFICATE-----
...省略
-----END CERTIFICATE-----
 1 s:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 High Assurance Server CA
   i:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert High Assurance EV Root CA
-----BEGIN CERTIFICATE-----
...省略
-----END CERTIFICATE-----
---
Server certificate
subject=/C=US/ST=California/L=San Francisco/O=GitHub, Inc./CN=www.github.com
issuer=/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 High Assurance Server CA
---
No client certificate CA names sent
Server Temp Key: ECDH, X25519, 253 bits
---
SSL handshake has read 3674 bytes and written 289 bytes
---
New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES128-GCM-SHA256
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
SSL-Session:
    Protocol  : TLSv1.2
    Cipher    : ECDHE-RSA-AES128-GCM-SHA256
    Session-ID: D11A4DD2C801FADA75D685893D661809EBCD8D1D071203A0681DC57959B69670
    Session-ID-ctx:
    Master-Key: 9CFDC956C3EB2BCCD5693041A34A92F43755D88172A5B1E72AFED2A77273F4593A3B0D1F52BA2A8F29A0B5AECF112F09
    TLS session ticket lifetime hint: 7200 (seconds)
    TLS session ticket:
    0000 - de 13 86 32 27 39 ff 04-80 a1 38 9b 76 32 8e d6   ...2'9....8.v2..
    0010 - 5f 7b 98 f4 1d 26 1e bf-03 ae 69 5d 3c fc 71 9c   _{...&....i]<.q.
    0020 - 09 77 f5 10 e7 c0 d2 b8-1c 6b f1 51 5d 26 25 3d   .w.......k.Q]&%=
    0030 - f9 c6 be 79 53 b0 37 0c-74 8a e8 72 67 00 72 aa   ...yS.7.t..rg.r.
    0040 - 2a 05 d7 07 fa 26 ca e4-ab c1 92 45 2f 01 6b a0   *....&.....E/.k.
    0050 - d9 14 4f bc 6c 85 43 c1-74 1f dd d9 56 b4 bf 8d   ..O.l.C.t...V...
    0060 - 16 d1 fa f0 68 b4 fd 4b-bd bd 2f e1 7b bc 16 cc   ....h..K../.{...
    0070 - 92 26 8c 2f b2 55 25 b4-79 b2 ab 34 2a 1a 1f f6   .&./.U%.y..4*...
    0080 - 85 a8 8d 9b 63 3f cd f4-d2 60 5c 2c 10 ac 99 06   ....c?...`\,....
    0090 - 1d 02 bc 78 ca 37 d2 65-46 7f 16 56 12 b1 e2 5f   ...x.7.eF..V..._

    Start Time: 1586685050
    Timeout   : 7200 (sec)
    Verify return code: 0 (ok)
---

Java代码扫描KeyStore中的证书有效期

KeyStore keyStore = KeyStore.getInstance(KeyStore.getDefaultType());
keyStore.load(new FileInputStream(new File(PATH)), PASSWORD.toCharArray());

Enumeration<String> aliases = keyStore.aliases();
while (aliases.hasMoreElements()) {
	String alias = aliases.nextElement();
	X509Certificate cert = (X509Certificate) keyStore.getCertificate(alias);
	try {
		cert.checkValidity(DateTime.now().toDate());
	} catch (CertificateExpiredException cee) {
        System.out.println("cert is expired.")
	} catch (CertificateNotYetValidException cnyve) {
		System.out.println("certi is not yet valid")
    }
}

5. 参考

  1. PKI from wikipedia
  2. X.509 from wikipedia
  3. 《HTTPS权威指南》
  4. Java Developer Guide to SSL VPN needed