TLS/SSL session resume on FTP transfer connection with OpenSSL

Question

I\'m open source developer implementing FTP client (WinSCP).

I\'m trying to resume TLS/SSL session from the FTP control socket on the transfer socket. Some FTP serve

Answer 1

You must specifically enable client session caching on your SSL_CTX object with:

SSL_CTX_set_session_cache_mode(ctx, SSL_SESS_CACHE_CLIENT);

You may also need to increase the default session cache timeout (the default is 300 seconds), using SSL_CTX_set_timeout().

(You must also be creating your SSL objects from the same SSL_CTX object).

Answer 2

Using the SSL_get1_session and the SSL_set_session worked in the end. I must have used them incorrectly when trying the first time.

• Once the TLS/SSL session on the control connection is established, use SSL_get1_session to retrieve the session. I specifically do it from a callback set by the SSL_set_info_callback, when where & SSL_ST_CONNECT.
• Call the SSL_set_session with the reference to the control connection session, when setting up TLS/SSL session for the data connection.