Hi Emilien,
As an alternative to NanoSSL, yaSSL has recently finished a port of the CyaSSL embedded SSL library to MQX/RTCS/MFS. You can read my original post, here:
CyaSSL embedded SSL now available for MQX!
CyaSSL supports both SSL client and server sides and supports protocols up to TLS 1.2 with DTLS.
Best Regards,
Chris