Implementing a custom cryptographic function

[Mehdi Asgari]

Hi
I want to develop a simple client/server OpenSSL application (a simple
"Hello Other Side" passing between the two);
my problem: Can I use a custom crypto API for encrypting data passed between
? (a simple XOR suffices, it's just proof of concept)
Could anyone please show me some hints ?
(I've searched the web but couldn't find anything useful)
Thanks in advance