DES encryption

If a DES key is specified in the Option/Connections dialogue, it will be is used to encrypt sound transmitted to that host using a slightly modified version of the Data Encryption Standard algorithm (the initial and final permutations, which do not contribute to the security of the algorithm and exist purely to deter software implementations of DES are not performed). In order to decrypt sound encoded with DES, the connection on the receiving machine must specify an identical DES key. The DES key phrase can be as long as 255 characters. The actual DES key is created by applying the MD5 algorithm to the given key phrase, then folding the resulting 128 bit digest into 56 bits with XOR and AND.

Speak Freely will continue to correctly receive unencrypted sound from a given host even if a DES key is specified for the connection as long as the remote host is transmitting in Speak Freely protocol. RTP and VAT protocols do not permit this, so you must clear the DES key for the connection to receive unencrypted RTP and VAT transmissions.