Clipper chip

The Clipper chip was a chipset that was developed and promoted by the United States National Security Agency (NSA) as an encryption device, with a built-in backdoor, intended to be adopted by telecommunications companies for voice transmission. It was announced in 1993 and by 1996 was entirely defunct.

The Clipper chip used a data encryption algorithm called Skipjack to transmit information and the Diffie-Hellman key exchange-algorithm to distribute the cryptokeys between the peers. Skipjack was invented by the National Security Agency of the U.S. Government; this algorithm was initially classified SECRET, which prevented it from being subjected to peer review from the encryption research community. The government did state that it used an 80-bit key, that the algorithm was symmetric, and that it was similar to the DES algorithm. The Skipjack algorithm was declassified and published by the NSA on June 24, 1998. The initial cost of the chips was said to be $16 (unprogrammed) or $26 (programmed), with its logic designed by Mykotronx, and fabricated by VLSI Technology, Inc (see the VLSI logo on the image on this page).

At the heart of the concept was key escrow. In the factory, any new telephone or other device with a Clipper chip would be given a cryptographic key, that would then be provided to the government in escrow. If government agencies "established their authority" to listen to a communication, then the key would be given to those government agencies, who could then decrypt all data transmitted by that particular telephone. The newly formed Electronic Frontier Foundation preferred the term "key surrender" to emphasize what they alleged was really occurring.

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