Unformatted text preview: about 42 minutes . This isn’t much help for Clipper voice conversations. Because the key exchange protocol is not part of the Clipper chip, the 42-minute brute-force attack must occur after key exchange; it cannot be done before making the telephone call. This attack may work for facsimile transmission or with the Fortezza card (see Section 24.17). Supposedly, the Clipper chip will resist reverse-engineering by “a very sophisticated, well-funded adversary” , but rumors are that Sandia National Laboratories successfully reverse-engineered one. Even if those rumors aren’t true, I suspect that the largest chip manufacturers in the world can reverse-engineer Clipper; it’s just a matter of time before someone with the right combination of resources and ethics comes along. Enormous privacy issues are associated with this scheme. Numerous civil liberty advocacy groups are actively campaigning against any key-escrow mechanism that gives the government the right to eavesdrop on citizens. But the sneaky thing is that this idea never went through Congress; NIST published the Escrowed Encryption Standard as a FIPS , bypassing that irritating legislative process. Right now it looks like the EES is dying a slow and quiet death, but standards have a way of creeping up on you. Anyway, Table 24.2 lists the different agencies participating in this program. Anyone want to do a threat analysis on having both escrow agents in the executive branch? Or on having escrow agents who really don’t know anything about the wiretap requests, and can do no more than blindly approve them? Or on having the government impose a secret algorithm as a commercial standard? In any case, implementing Clipper raises enough problems to question its value in court. Remember, Clipper only works in OFB mode. Despite what you may have been told to the contrary, this does not provide integrity or authentication. Imagine that Alice is on trial, and a Clipper-encrypted telephone call is part of the evidence. Alice claims that she never made the call; the voice is not hers. The phone’s compression algorithm is so bad...
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- Fall '10
- Cryptography, Bruce Schneier, Applied Cryptography, EarthWeb, Search Search Tips