re off the shelf cheap des keyseach machine was re corporate acceptance of the wiretap chip smb research att com steven bellovin writes thousands tens of thousands do some arithmetic please skipjack has possible keys let s assume a brute force engine like that hypothesized for des microsecond per trial million chips that s trials per second or about years for trials well maybe they can get chips running at one trial per nanosecond and build a machine with million chips sure only years for each solution but there is a much more pernicious problem with the scheme as proposed building a brute force machine to test possible keys if you have the other half from one escrow agent is easy one chip one test per microsecond gives you one break every two weeks and that break gives you all messages involving that phone the xor scheme so that the files from one escrow agent gives you nothing is an improvement but notice that xoring with truely random bit strings allows for an arbitrary number of escrow agents using for xor sk for the escrowed key and a and b for two random bit strings hand sk a b sk a and sk b to three escrow agents it is possible to come with an encoding scheme to match any escrow pattern for example of such that fewer cooperating escrow agents gives the cracking agency no benefit robert i eachus with standard disclaimer use standard disclaimer function message text in clever ideas return better ideas is
