Cipher Suites

简介

Cipher Suite 在 TLS 中用来指定整个通信过程中所使用的加密相关的参数，包括如何协商加密得到加密所用的密钥，以及签名使用的算法和哈希算法。

主要涉及到下面几个方面：

Key exchange (Key 交换算法)
Bulk encryption （批量加密）
Message authentication (消息认证)
Authentication

Key 交换算法 用户交换一个叫做 Shared key 的私钥。这里主要使用非对称加密算法(asymmetric key algorithm). 这个key 将作为种子，用来生成多个密钥，生成的密钥将用于保护不同的数据。

因为非堆成加密的特性，它只被用来加密少量的数据。大量数据的情况下，性能会很低，因此不用它来做大数据量的加密操作。

Bulk encryption 用来加密客户端和服务器的通信数据。不同与非对称加密算法，这些算法可以用来进行大量数据的加密，而且性能比非对称加密算法强很多。

Message authentication 算法用来生成消息的哈希，签名等，用来确保消息的完整性。

TLS 中如何协商 Cipher Suite？

TLS 协议中通过 ClientHello 和 SeverHello 两个包来协商当前链接将要使用的 CipherSuite.

客户端将自己支持的所有 Cipher Suite 的列表，放入 ClientHello 中，发送给服务器端。

服务器端收到 ClientHello 后，从中选择自己也支持的 CipherSuite，然后将选中的结果放在 ServerHello 中发送给客户端。

CipherSuite 列表中，放在最前面的值是客户端最想要的值。

示例

// ClientHello
Transport Layer Security
    TLSv1.2 Record Layer: Handshake Protocol: Client Hello
        Content Type: Handshake (22)
        ...
        Handshake Protocol: Client Hello
            Handshake Type: Client Hello (1)
            ...
            Cipher Suites (18 suites)
                Cipher Suite: TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 (0xc02b)
                Cipher Suite: TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (0xc02f)
                Cipher Suite: TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 (0x009e)
                Cipher Suite: TLS_RSA_WITH_AES_128_GCM_SHA256 (0x009c)
                Cipher Suite: TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA (0xc00a)
                Cipher Suite: TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA (0xc014)
                Cipher Suite: TLS_DHE_RSA_WITH_AES_256_CBC_SHA (0x0039)
                Cipher Suite: TLS_RSA_WITH_AES_256_CBC_SHA (0x0035)
                Cipher Suite: TLS_ECDHE_ECDSA_WITH_RC4_128_SHA (0xc007)
                Cipher Suite: TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA (0xc009)
                Cipher Suite: TLS_ECDHE_RSA_WITH_RC4_128_SHA (0xc011)
                Cipher Suite: TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA (0xc013)
                Cipher Suite: TLS_DHE_RSA_WITH_AES_128_CBC_SHA (0x0033)
                Cipher Suite: TLS_DHE_DSS_WITH_AES_128_CBC_SHA (0x0032)
                Cipher Suite: TLS_RSA_WITH_RC4_128_SHA (0x0005)
                Cipher Suite: TLS_RSA_WITH_RC4_128_MD5 (0x0004)
                Cipher Suite: TLS_RSA_WITH_AES_128_CBC_SHA (0x002f)
                Cipher Suite: TLS_RSA_WITH_3DES_EDE_CBC_SHA (0x000a)
            Compression Methods Length: 1
            Compression Methods (1 method)
            ...

// ServerHello
Transport Layer Security
    TLSv1.2 Record Layer: Handshake Protocol: Server Hello
        Content Type: Handshake (22)
        Version: TLS 1.2 (0x0303)
        Length: 81
        Handshake Protocol: Server Hello
            Handshake Type: Server Hello (2)
            Length: 77
            Version: TLS 1.2 (0x0303)
            Random: 8566d75a1...
            Session ID Length: 32
            Session ID: 51ff379f32....
            Cipher Suite: TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (0xc02f)
            Compression Method: null (0)
            Extensions Length: 5
            Extension: renegotiation_info (len=1)
            ....

Cipher Suites 示例:

截止 TLS1.2，已经有特别多的 CipherSuite 可供选择了。这里，我们列举一些作为例子：

`TLS_RSA_WITH_NULL_SHA256`

Key Exchange: Rivest Shamir Adleman algorithm (RSA)

Authentication: Rivest Shamir Adleman algorithm (RSA)

Encryption: NULL Encryption (NULL)

Hash: Secure Hash Algorithm 256 (SHA256)

`TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA`

Key Exchange: Elliptic Curve Diffie-Hellman Ephemeral (ECDHE)

Authentication: Rivest Shamir Adleman algorithm (RSA)

Encryption: Advanced Encryption Standard with 128bit key in Cipher Block Chaining mode (AES 128 CBC)

Hash: Secure Hash Algorithm 1 (SHA)

`TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384`

Key Exchange: Elliptic Curve Diffie-Hellman Ephemeral (ECDHE)

Authentication: Elliptic Curve Digital Signature Algorithm (ECDSA)

Encryption: Advanced Encryption Standard with 256bit key in Cipher Block Chaining mode (AES 256 CBC)

Hash: Secure Hash Algorithm 384 (SHA384)

`TLS_AES_256_GCM_SHA384`

Key Exchange: —

Authentication: —-

Encryption: Advanced Encryption Standard with 256bit key in Galois/Counter mode (AES 256 GCM)

Hash: Secure Hash Algorithm 384 (SHA384)

`TLS_DHE_RSA_WITH_AES_256_CBC_SHA`

Key Exchange: Diffie-Hellman Ephemeral (DHE)

Authentication: Rivest Shamir Adleman algorithm (RSA)

Encryption: Advanced Encryption Standard with 256bit key in Cipher Block Chaining mode (AES 256 CBC)

Hash: Secure Hash Algorithm 1 (SHA)

`TLS_DHE_DSS_WITH_AES_256_CBC_SHA`

Key Exchange: Diffie-Hellman Ephemeral (DHE)

Authentication: Digital Signature Standard (DSS)

Encryption: Advanced Encryption Standard with 256bit key in Cipher Block Chaining mode (AES 256 CBC)

Hash: Secure Hash Algorithm 1 (SHA)

`TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA`

Key Exchange: Diffie-Hellman (DH)

Authentication: Anonymous (anon)

Encryption: Data Encryption Standard with 40bit key in Cipher Block Chaining mode (DES40 CBC)

Hash: Secure Hash Algorithm 1 (SHA)

`TLS_ECDH_ECDSA_WITH_ARIA_128_CBC_SHA256`

Key Exchange: Elliptic Curve Diffie-Hellman (ECDH)

Authentication: Elliptic Curve Digital Signature Algorithm (ECDSA)

Encryption: ARIA with 128bit key in Cipher Block Chaining mode (ARIA 128 CBC)

Hash: Secure Hash Algorithm 256 (SHA256)

简介