A CDE Definition

A symmetric cryptographic algorithm developed by the U.S. National Security Agency (NSA). It is used in the Department of Commerce's Escrowed Encryption Standard (EES), which was embodied in the CLIPPER chip.

The key to the encrypted message is itself encrypted with a key combined from two escrowed keys. The encrypted key and an identifier of the chip that sent it is encrypted again with a "family key." In this way, a law enforcement agency can use the family key to decrypt the outer layer and glean the chip ID, which is used to obtain the two escrowed keys that are combined to decrypt the key that decrypts the message. Skipjack uses an 80-bit key to encrypt 64-bit blocks, but algorithm details are classified. See CLIPPER chip.

A cryptography chip used by the U.S. government for telephone security that used the SkipJack algorithm and provided for key escrow. The federal government tried to make CLIPPER a universal method, because it alone could unscramble the data if required using independently-stored fragments of the Law-Enforcement Access Field (LEAF), which could be reassembled into a decryption key. The CLIPPER chip also included the CAPSTONE chip, which provided the actual cryptographic processing.

The proposal failed because of widespread rejection by the cryptographic community, which pointed out that nothing would preclude encrypting telephone transmissions with some other method before using a CLIPPER-chip equipped telephone unit. See Skipjack algorithm.