AN4683 Datasheet, PDF (6/31 Pages) STMicroelectronics – Transport layer security protocol for SPWFxxx module

SSL/TLS protocol overview
AN4683
Note:
Note:
The client and the server must support at least one common cipher suite, otherwise the
handshake protocol fails. The server generally chooses the strongest common cipher suite
they both support.
3. The server sends its digital certificate in an optional certificate message. For example,
the server uses X.509 digital certificates.
4. Additionally, a ServerKeyExchange message may be sent, if it is required (e.g., if the
server has no certificate, or if its certificate is for signing only).
5. If the server requires a digital certificate for client authentication, an optional
CertificateRequest message is appended.
6. The server sends a ServerHelloDone message indicating the end of this phase of
negotiation.
7. If the server has sent a CertificateRequest message, the client must send the
Certificate message. For example the client uses an X.509 digital certificate.
8. The client sends a ClientKeyExchange message. This message contains the
premaster secret used in the generation of the symmetric encryption keys and the
message authentication code (MAC) keys. The client encrypts the pre-master secret
with the public key of the server.
The public key is sent by the server in the digital certificate or in ServerKeyExchange
message.
9. If the client sent a digital certificate to the server, the client sends a CertificateVerify
message signed with the client's private key. By verifying the signature of this
message, the server can explicitly verify the ownership of the client digital certificate.
10. The client sends a ChangeCipherSpec message announcing that the new parameters
(cipher method, keys) have been loaded.
11. The client sends a finished message. It is the first message encrypted with the new
cipher method and keys.
12. The server responds with a ChangeCipherSpec and a finished message from its end.
13. The SSL handshake protocol ends and the encrypted exchange of application data can
be started.
During the initial handshaking phase, the client and server negotiate cipher suites, which
specify a cipher for each of the following functionalities:
Functionality
Authentication
Key-exchange/agreement
Symmetric ciphers for encryption
Hash
Table 1. Ciphers
Cipher
RSA, DSA, ECDSA
RSA, DH, ECDH, SRP, PSK
RC4, IDEA, DES, 3DES, AES or Camellia.
MAC (for SSLv3.0) or HMAC with MD2, MD4, MD5, SHA-1,
SHA-256 (after TLSv1.1 and 1.2 standards).
A complete list of SSL/TLS cipher suites can be found in the registry maintained by the
Internet assigned numbers authority (IANA) (see [6] in References).
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