At 11:31 PM 10/9/97 -0400, an Anonymous Monty Cantsin wrote:
My apologies if this has already been discussed, but wouldn't this be a straightforward solution?
Yes, your PGP solution will work. Information-theoretically speaking, it's a simple XOR, and is as secure as the random number generator used and the PGP systems used to exchange your secret key. However, so will a thousand other schemes that use PGP, or any other "out-of-band" form of authentication. At this point you realize that you are using PGP for authentication, not the "Secure Phone". Our discussion so far has been ways of authenticating the connection WITHOUT external references. No pre-exchanged public keys, no pre-arranged passwords or secrets or any of that. (They even disallowed me a trip to ask a trusted authorizer!) To restate the problem in its current form: using the secure phone channel, (and only the secure phone channel) can we "prove" that we are connecting only two endpoints, and that there is no man-in-the-middle between the voices that are speaking to each other? Remember that Mallory (the man in the middle) has full knowledge of the protocol and of the public keys belonging to both parties. He can even spoof the voices. The latest candidates for solutions have been "have the users identify this flaw in the audio" which is probably as good as we can hope for on an unauthenticated conversation. As it is, Eric's current solution to have each party simply read their half of the hash. Real-time impersonating the audio to the point where you can fool a careful human is already putting a great deal of exposure risk on Mallory. My bottom line: I would trust Eric's current phone to all but eliminate the MITM, and with external authentication I wouldn't have any problems at all. John -- J. Deters "Don't think of Windows programs as spaghetti code. Think of them as 'Long sticky pasta objects in OLE sauce'." +--------------------------------------------------------------------+ | NET: mailto:jad@dsddhc.com (work) mailto:jad@pclink.com (home) | | PSTN: 1 612 375 3116 (work) 1 612 894 8507 (home) | | ICBM: 44^58'36"N by 93^16'27"W Elev. ~=290m (work) | | For my public key, send mail with the exact subject line of: | | Subject: get pgp key | +--------------------------------------------------------------------+