Perry answered most of my questions with the new information that the checksum is a function of the IV and session key. That still leaves one big one unanswered: Doesn't the Clipper chip at the other end of the message have to compute and send a LEAF too? Otherwise there would be no way for the wiretappers to identify it. And that LEAF will contain the proper session key unless both ends are using the same hack. Also, what does Clipperphone have that the Tessera board doesn't which keeps this hack from working? Is enough known about the workings of the two so that someone could build a computer-based telephone using Tessera that would be compatible with Clipperphone yet use this hack? -- sidney <sidney@taurus.apple.com>