Re: A Nice Summary of Motives for Clipper
Several people on sci.crypt have pointed to the following paragraph in Matt Blaze's report of the NSA briefing on Clipper, posted here and in the newsgroups:
Clipper chips should be available (to product vendors) in June. You can't just buy loose chips - they have to be installed in approved products. Your application interface has to be approved by NIST for you to get your hands on the chips.
This could explain a lot. In particular, if they can enforce this, it could put an end to the dreams of multiple encryption. For months people have been saying, "Clipper? No problem. I'll just encrypt with PGP then pass it through Clipper and the Feds won't ever guess! Ha, ha, ha!" Maybe this won't be so easy. From Blaze's description it sounds like such devices wouldn't be approved. It could be the only Clipper phones will be ones that don't do anything to keep the Feds from picking up the conversation. People could still build non-Clipper encrypting phones (assuming that the constant rumors of threatening midnight visits from NSA agents are false), but the users of those phones could no longer blend in with the Clipper traffic. Hal
(I've changed the article title to reflect my point here.) Hal Finney writes: ...
This could explain a lot. In particular, if they can enforce this, it could put an end to the dreams of multiple encryption. For months people have been saying, "Clipper? No problem. I'll just encrypt with PGP then pass it through Clipper and the Feds won't ever guess! Ha, ha, ha!"
Maybe this won't be so easy. From Blaze's description it sounds like such devices wouldn't be approved. It could be the only Clipper phones will be ones that don't do anything to keep the Feds from picking up the conversation.
People could still build non-Clipper encrypting phones (assuming that the constant rumors of threatening midnight visits from NSA agents are false), but the users of those phones could no longer blend in with the Clipper traffic.
For voice use, this may be so (but I think pre-encryption before Clipper is still possible....see discussion at the end). But for the forthcoming _data encryption_ use (Skipjack, etc.), I don't see how "pre-encryption" can be detected, much less blocked, banned, or otherwise interfered with. After all, "data are data." Frankly, it has always been the (presumably) impending restrictions on data encryption that have worried me the most, because it is the application of strong crypto to data encryption that holds the most promise (in such things as digital money, remailers, all the stuff we deal with here on this list). Voice scrambling has never been a high priority for me, personally. Requiring Skipjack encryption for all packets entering the Federal Interstate Dataway (tm) could be a constraining hassle, but what's _inside_ those Skipjacked packets could be arbitrary. (Even an "entropy" filter as part of Skipjack--an implausible complication--could easily be defeated.) If the government requires Skipjack, I can't see any way of preventing pre-encryption, short of "random searches" (analogous to random searches of cargo to detect contraband, etc.). And I suspect some clever work could allow pre-encryption even with Clipper. After all, if the canonical (expected) mode is for two Clipper users to be speaking English to each other, and they start to speak Croation, this is a crude form of encryption (security through obscurity, for a few minutes at least). Even more so if they started speaking their own private code. Clipper would just take the audio signal, manipulate it as it is supposed to, send it, etc. Thus, putting one's own cipher system in _front_ of Clipper (and _after_ it at the receiving end, of course) should work, providing the output of the cipher system is standard audio (constrained by the phone system(s) used). But isn't this exactly what existing secure phones are (like the STU-III)? That is, nothing inside the Clipperphone need be touched or interfaced with. Just use the Clipperphone as usual, but speak in a "language" that cannot be deciphered by the surveillors, even if they get a warrant to look at the Clipper keys. Am I missing something? --Tim May -- .......................................................................... Timothy C. May | Crypto Anarchy: encryption, digital money, tcmay@netcom.com | anonymous networks, digital pseudonyms, zero 408-688-5409 | knowledge, reputations, information markets, W.A.S.T.E.: Aptos, CA | black markets, collapse of governments. Higher Power:2**859433 | Public Key: PGP and MailSafe available.
Let me briefly elaborate on a point I made in my last post:
For voice use, this may be so (but I think pre-encryption before Clipper is still possible....see discussion at the end). But for the forthcoming _data encryption_ use (Skipjack, etc.), I don't see how "pre-encryption" can be detected, much less blocked, banned, or otherwise interfered with. After all, "data are data."
In both this data case and the Clipper voice case, I am assuming the keys for the pre-encryption are negotiated by either prearrangement or by some back-channel, and don't involve D-H or any other such protocol through the Skipjack or Clipper system. (Perhaps this situation, where a bunch of key exchange protocols must be gone through before communication takes place, is what Hal Finney was referring to when he said that the Clipper proposal looks like it will make multiple encryption impossible.) Most of my (few) encrypted communications are by this kind of prearrangement, with PGP being the most obvious case of this, and so a multiple encryption scheme is workable. With voice encryption, I guess the Clipper system will not be very cooperative with D-H and similar protocols. But it will still be possible: 1. Use the Clipperphone to establish who one is communicating with. Alice and Bob thus start talking to each other. 2. Alice says: "Switch to PGP-Voice with my P-K" (and so on). 3. Bob and Alice are thus communicating with PG-Voice, with Clipper doing a further encryption. If the Feds get a warrant to get the Clipper keys, then all they get is PGP-Voice-encrypted junk. Clipper then serves the admirable purpose of _covering_ the further use of encryption! --Tim May -- .......................................................................... Timothy C. May | Crypto Anarchy: encryption, digital money, tcmay@netcom.com | anonymous networks, digital pseudonyms, zero 408-688-5409 | knowledge, reputations, information markets, W.A.S.T.E.: Aptos, CA | black markets, collapse of governments. Higher Power:2**859433 | Public Key: PGP and MailSafe available.
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