If a Blowfish key is specified in the Option/Connections dialogue, it will be is used to encrypt sound transmitted to that host with the Blowfish Encryption Algorithm. In order to decrypt sound encoded with Blowfish, the connection on the receiving machine specify an identical Blowfish key. The Blowfish key phrase can be as long as 255 characters. The actual Blowfish key is created by applying the MD5 algorithm to the given key phrase to create the 128 bit Blowfish key.
Blowfish encryption is much faster and generally considered to be more secure than DES encryption. However, Blowfish is newer and has not been formally adopted by governments or standards organisations.
Cipher block chaining is used within each sound packet, but not from packet to packet. If that were done, loss of a single packet would render the entire rest of the conversation unintelligible.
Speak Freely will continue to correctly receive unencrypted sound from a given host even if a Blowfish key is specified for the connection.
The Blowfish algorithm has been placed in the public domain and may be used in any manner, commercial or noncommercial, without a license.
Since Blowfish encryption is not specified as a part of the RTP and VAT protocols, it can be used only when transmitting in Speak Freely protocol.