This interesting report on the Clipper/Capstone/Tessera Key Escrow system was posted by Matt Blaze to several groups. I hope most of you have seen it already, but for those who haven't, here it is. Apologies for using bandwidth to reproduce an article here, but I think the machinations over Clipper and key escrow in general are pretty germane to the Cypherpunks charter. --Tim May Newsgroups: sci.crypt,talk.politics.crypto,comp.org.eff.talk,alt.privacy.clipper From: mab@research.att.com (Matt Blaze) Subject: Notes on key escrow meeting with NSA Organization: AT&T Date: Wed, 2 Feb 1994 21:02:55 GMT Message-ID: <mab.760222975@merckx> A group from NSA and FBI met the other day with a group of us at Bell Labs to discuss the key escrow proposal. They were surprisingly forthcoming and open to discussion and debate, and were willing to at least listen to hard questions. They didn't object when asked if we could summarize what we learned to the net. Incidentally, the people at the meeting seemed to base a large part of their understanding of public opinion on Usenet postings. Postings to sci.crypt and talk.politics.crypto seem to actually have an influence on our government. A number of things came out at the meeting that we didn't previously know or that clarified previously released information. What follows is a rough summary; needless to say, nothing here should be taken as gospel, or representing the official positions of anybody. Also, nothing here should be taken as an endorsement of key escrow, clipper, or anything else by the authors; we're just reporting. These notes are based on the collective memory of Steve Bellovin, Matt Blaze, Jack Lacy, and Mike Reiter; there may be errors or misunderstandings. Please forgive the rough style. Note also the use of "~ ~" for 'approximate quotes' (a marvelous Whit Diffie-ism). NSA's stated goals and motives for all this: * DES is at the end of its useful life * Sensitive, unclassified government data needs protection * This should be made available to US Citizens * US business data abroad especially needs protection * The new technology should not preclude law enforcement access They indicated that the thinking was not that criminals would use key escrowed crypto, but that they should not field a system that criminals could easily use against them. The existence of key escrow would deter them from using crypto in the first place. The FBI representative said that they expect to catch "~only the stupid criminals~" through the escrow system. Another stated reason for key escrow is that they do not think that even government-spec crypto devices can be kept physically secure. They do expect enough to be diverted to the black market that they feel they need a response. NSA's emphasis was on the foreign black market... There seems to be a desire to manipulate the market, by having the fixed cost of key escrow cryptography amortized over the government market. Any private sector devices would have to sell a much larger number of units to compete on price. (This was somewhere between an implication and an explicit statement on their part.) When asked about cryptography in software, "~...if you want US government cryptography, you must do it with hardware~". 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. An interesting point came up about the reverse-engineering resistance of the chips: they are designed to resist reverse engineering the data in the chip without destroying the chip. It is not clear (from the information presented at the meeting) whether the chips are equally resistant to destructive reverse-engineering to learn the skipjack algorithm. They said the algorithm was patented, but they may have been joking. ("~And if that doesn't scare you enough, we'll turn the patent over to PKP.~") The resistance to reverse engineering is not considered absolute by NSA. They do feel that "~it would require the resources of a national laboratory, and anyone with that much money can design their own cryptosystem that's just as strong.~" They repeated several times that there are "~no plans to regulate the use of alternate encryption within the US by US citizens.~" They also indicated they "~weren't naive~" and didn't think that they could if they wanted to. There were 919 authorized wiretaps, and 10,000 pen register monitors, in 1992. They do not have any figures yet on how often cryptography was used to frustrate wiretaps. They do not yet have a production version of the "decoder" box used by law enforcement. Initially, the family key will be split (by the same XOR method) and handled by two different people in the athorized agencies. There is presently only one family key. The specifications of the escrow exploitation mechanism are not yet final, either; they are considering the possibility of having the central site strip off the outer layers of encryption, and only sending the session key back to the decoder box. The escrow authorities will NOT require presentation of a court order prior to releasing the keys. Instead, the agency will fill out a form certifying that they have a legal authorization. This is also backed up with a separate confirmation from the prosecutor's office. The escrow agencies will supply any key requested and will not themselves verify that the keys requested are associated with the particular court order. The NSA did not answer a question as to whether the national security community would obtain keys from the same escrow mechanism for their (legally authorized) intelligence gathering or whether some other mechanism would exist for them to get the keys. The masks for the Clipper/Capstone chip are unclassified (but are protected by trade secret) and the chips can be produced in an unclassified foundry. Part of the programming in the secure vault includes "~installing part of the Skipjack algorithm.~" Later discussion indicated that the part of the algorithm installed in the secure vault are the "S-tables", suggesting that perhaps unprogrammed Clipper chips can be programmed to implement other 80-bit key, 32 round ciphers. The Capstone chip includes an ARM-6 RISC processor that can be used for other things when no cryptographic functions are performed. In particular, it can be used by vendors as their own on-board processor. The I/O to the processor is shut off when a crypto operation is in progress. They passed around a Tessera PCMCIA (type 1) card. These cards contain a Capstone chip and can be used by general purpose PC applications. The cards themselves might not be export controlled. (Unfortunately, they took the sample card back with them...) The card will digitally sign a challenge from the host, so you can't substitute a bogus card. The cards have non-volatile onboard storage for users' secret keys and for the public keys of a certifying authority. They are building a library/API for Tessera, called Catapult, that will provide an interface suitable for many different applications. They have prototype email and ftp applications that already uses it. They intend to eventually give away source code for this library. They responded favorably to the suggestion that they put it up for anonymous ftp. Applications (which can use the library and which the NSA approves for government use) will be responsible for managing the LEAF field. Note that they intend to apply key escrowed Skipjack to other applications, including mail and file encryption. The LEAF would be included in such places as the mail header or the file attributes. This implies that it is possible to omit sending the LEAF -- but the decrypt chip won't work right if it doesn't get one. When asked, they indicated that it might be possible wire up a pair of Clipper/Capstone chips to not transmit the LEAF field, but that the way to do this is "~not obvious from the interface we give you~" and "~you'd have to be careful not to make mistakes~". They gave a lot of attention to obvious ways to get around the LEAF. The unit key is generated via Skipjack itself, from random seeds provided by the two escrow agencies (approximately monthly, though that isn't certain yet). They say they prefer a software generation process because its correct behavior is auditable. Capstone (but not Clipper) could be configured to allow independent loading of the two key halves, in separate facilities. "~It's your money [meaning American taxpayers].~" The LEAF field contains 80 bits for the traffic key, encrypted via the unit key in "~a unique mode <grin>~", 32 bits for the unit id, and a 16 bit checksum of some sort. (We didn't waste our breath asking what the checksum algorithm was.) This is all encrypted under the family key using "~another mode <grin>~". They expressed a great deal of willingness to make any sort of reasonable changes that vendors needed for their products. They are trying *very* hard to get Skipjack and key escrow into lots of products. ***end of article***