Stunnel is a "Secure Tunnel" that allows normal, unencrypted programs to have a secure link over the network using SSL. It is simpler than IPSEC and less complex than SSH since it doesn't use public key-based authentication.
From their homepage:
- Stunnel is a program that allows you to encrypt arbitrary TCP connections inside SSL (Secure Sockets Layer) available on both Unix and Windows. Stunnel can allow you to secure non-SSL aware daemon and protocols (like POP, IMAP, LDAP, etc) by having Stunnel provide the encryption, requiring no changes to the daemon's code.