Computer Security and Cryptography

18.8 THE SECURE SOCKET LAYER (SSL)

SSL was originated by Netscape; it consists of several upper layer protocols⁵ by which a pair of users – the Client and the Server – agree on a key exchange method, an encipherment algorithm, and a message digest.

In what follows we go through the Handshake Protocol initiated by a client.

Phase 1 – Client Initiation The Client proposes the following (Fig. 18.11).

Figure 18.11 SSL Phase 1 (Client_Hello).

1. A key exchange protocol. Possible choices include
   • RSA,
   • Diffie–Hellman.
2. A data encipherment algorithm. Possible choices include
   • DES and DES3,
   • AES,
   • IDEA,
   • RSA's RC2 and RC4.
3. A message digest algorithm. Possible choices include
   • RSA's MD5,
   • NIST's SHA.
4. A random number referred to as random_bytes [28 bytes].
5. A session ID designated as SessionID [variable length].
6. A (lossless) compression method identifier [integer 1 ≤ C_ID < 511]; a complete specification is not included in the latest SSL-Specification.

Phase 1 – Server Response to Client_Hello: The Server accepts one of the choices made in the Client_Hello messages (Fig. 18.12).

Phase 2 – Server Authentication and Key Exchange: The Server delivers its certificate; when authentication/secrecy is enabled there is a key exchange. The Server requests a certificate from the Client (Fig. 18.13).

Figure 18.12 Server response to Client_Hello.

Figure 18.13 SSL Phase 2 – server authentication and ...