SSL.protocol.txt

         
   SSL   
         


Main:
  - over TCP
  - usually used by HTTP to provide confidentialy and authentication -> HTTPS
     - all HTTP is encrypted, but not TCP layer, so host+port information is not encrypted
     - can also infer session duration, and content length
  - port 443
  - previously SSL, now TLS (prefer TLS 1.2, supported by all browsers except IE10< and Safari Windows)

Protocol:
  - session establishing (client authentication optional):
     - client sends TLS params (TSL version supported, cipher and compression supported, a random number)
     - server chooses protocols (sends them) and sends server certificate.
     - client checks server certificate matches servers domain/identity. 
       If authentication problems, reaction depends on client: can stop, ignore or warn user (what web browsers do)
     - client creates a pre-master secret, and sends it encrypted with server's public key. 
       Also sends client certificate.
     - server checks client certificate. Authentication problems reaction: same as client.
     - server decrypts pre-master secret (with its private key), and creates the final master secret by encrypting with
       client public key.
     - finishing handshakes (encrypted)
  - data exchange:
     - use shared master secret to generate session keys at known intervals, then use symetric cipher with it
  - can choose between several asym. (RSA, [ephemeral] [eliptic] Diffie-Hellman, PSK) and sym. ciphers (AES, Camelia,
    SEED, Chacha20, IDEA) with different modes of operation.
      - forward secrecy:
         - if one private key is compromised, cannot guess session keys (so can compromise future communication, but not past)
         - only with ephemeral [eliptic] Diffie-Hellman
  - session ID (optional):
     - goal is to renegociate new sessions without spending too much time
     - server keep session ID associated with shared master secret, and sends it to client who associates it with
       server's host+port. 
     - client asks for new session with session ID, and servers acknowledges it, using the stored shared master secret.
  - session tickets (optional, avoid it):
     - like session ID, but stores only on the client (server has methods to verify it with its private key)
  - NPN (Next Protocol Negocation):
     - choosing which application protocols can be built on top of SSL, with priority order.
     - client needs to be NPN-enabled, i.e. specifying a protocol
     - ALPN: new version
  - SNI (Server Name Indication):
     - sharing one SSL server for different hosts with different certificates
        - allows virtual hosting: one server IP for several HTTPS websites, without having a certificate with several domains
          shared by all websites
        - also more flexible to create new certificate for each new hos, instead of creating one new big certificate everytime
          there is a new host
     - client needs to be SNI-enabled, i.e. specifying a hostname (not only host IP) to connect to as part of the SSL handshake