One of the first secure telephony programs. Not limited to VOIP but can also directly encrypt a telephone line by using modems. Calls are encrypted using Diffie-Hellmann key exchange and several symmetric ciphers.
Download is possible from Germany only, see homepage
OSP Module enables SER (SIP Express Router) to use the Open Settlement Protocol for secure Authorization, Routing and Accounting. OSP is an ETSI protocol, Technical Specification 101 321