A few similar commercial programs have been distributed without source, so that their security cannot be independently examined. Nautilus uses your computer's audio hardware to digitize and play back your speech using homebrew speech compression functions built into the program. It encrypts the compressed speech using your choice of the Blowfish, Triple DES, or IDEA block ciphers, and transmits the encrypted packets over your modem to your friend's computer. At the other end, the process is reversed. Nautilus itself does not currently incorporate any form of public key cryptography.
Further details are in the release notes included with the program.
We don't like this law but have to abide by it while it is in effect. Nautilus is distributed through export-restricted FTP sites for this reason. Export it at your own risk. Although we've done our best to choose secure ciphers and protocols for Nautilus, its design details have not yet been reviewed by anyone except the authors, and it's VERY EASY to make mistakes in such programs that mess up the security. We advise against putting too much faith in the security of the program until it has undergone a lot more reviewing and debugging.