SSL is the Secure Socket Layer. It is a protocol that encrypts a single TCP session. Using this Asymmetric Encryption, all data exchanged over a TCP socket can be cryptographically protected. SSL is the base of HTTPS - the secure World-Wide Web protocol.
SSL was designed by Netscape using algorithms invented by RSA (Rivest-Shamir-Adelman). Commercial implementations may be purchased from RSA. A free and robust implementation called SSLeay is also internationally available. Check your local legislation about Encryption to see if your government will let you download and use this software.