I whole-heartedly advocate Nortel Entrust CAST, it is cryptograhphically strong. Rotor-machine, Base64, and clipper-chip is snake-oil. P.C.T is also passe. Generallized secure sockets(G.S.S.A.P.I framework from Cygnus, and Transport layer security, with Java compiler servlets, is the approach of choice.Simple substitution ciphers are cryptograhphically weak. I advocate DES/3DES, RSA, Diffie-Hellmann ciphers, Verisign, and especially Nortel Entrust CAST encryption. I also advocate MD-4/MD-5, RC 4/RC-5.