Set the TLS security level early and on context

[DimitriPapadopoulos]

The existing code does work for cipher negotiation with old (FortiOS 4?) FortiGate appliances, but not for personal certificates (SHA-1 certificates).

Two reasons I can see:

• SSL_set_cipher_list() was called after messing with certificates.
• SSL_set_cipher_list() applies only to the SSL connection, not to certificates, call SSL_CTX_set_cipher_list() on context instead.

This change addresses both of the above issues.

See SSL(7) man page:

SSL_CTX (SSL Context)
This is the global context structure which is created by a server or client once per program life-time and which holds mainly default values for the SSL structures which are later created for the connections.

SSL (SSL Connection)
This is the main SSL/TLS structure which is created by a server or client per established connection. This actually is the core structure in the SSL API. At run-time the application usually deals with this structure which has links to mostly all other structures.

[DimitriPapadopoulos]

Unfortunately this does not help with #682. Will need to generate an SHA-1 certificate to investigate.

[DimitriPapadopoulos]

@martinetd In order to support SHA-1 personal certificates (see #682), I have decided to call SSL_CTX_set_min_proto_version() and SSL_CTX_set_cipher_list() on the ctx context instead of calling SSL_set_min_proto_version() and SSL_set_cipher_list() on the ssl connection only. Does this sound OK to you?

[martinetd]

Thanks for the @ mention -- it looks safe to me, man page says "The list of ciphers is inherited by all ssl objects created from ctx." and it is create afterwards so should be ok.

(While I'm on the man page I see this doesn't affect TLSv1.3, which should use SSL_CTX_set_ciphersuites instead.. but the default value looks sensible enough so I guess we don't need to; anyway unrelated to this change)

[DimitriPapadopoulos]

Thank you for looking into this. About TLSv1.3, see #687.

[mrbaseman]

this makes sense to me (although I have to admit that am not so familiar with the internals of openssl). I have tested this with one of my vpns where I'm using a client certificate to log in. At least this is not broken. I'm not sure how I could test if this solves the problem that it aims to address, but I think in #682 this has already been confirmed.