Home > Skipjack (cipher)

1 History of Skipjack

Skipjack was proposed as the encryption algorithm in a US government-sponsored scheme of key escrow, and the cipher was provided for use in the Clipper chip, implemented in tamperproof hardware. The design was originally secret, and was regarded with considerable suspicion by many in the public cryptography community for that reason. It was declassified on 24 June 1998.

To ensure public confidence in the algorithm, several academic researchers from outside the government were called in to evaluate the algorithm (Brickell et. al., 1993). The researchers found no problems with either the algorithm itself or the evaluation process. Moreover, their report gave some insight into the (classified) history and development of Skipjack:

[Skipjack] is representative of a family of encryption algorithms developed in 1980 as part of the NSA suite of " Type I" algorithms... SKIPJACK was designed using building blocks and techniques that date back more than forty years. Many of the techniques are related to work that was evaluated by some of the world's most accomplished and famous experts in combinatoricsCombinatorics Discrete mathematics Combinatorics is a branch of mathematics that studies finite collections of objects that satisfy specified criteria, and is in particular concerned with "counting" the objects in those collections enumerative combinatori and abstract algebraAbstract algebra Abstract algebra is the field of mathematics concerned with the study of algebraic structures such as groups, rings and fields. The term "abstract algebra" is used to distinguish the field from " elementary algebra" or "high school algebr. SKIPJACK's more immediate heritage dates to around 1980, and its initial design to 19871987 is a common year starting on Thursday. Events January January 1 Nunavut's capital changes it name to Iqaluit from Frobisher Bay. January 3 Aretha Franklin becomes the first woman inducted into the Rock and Roll Hall of Fame. January 4 An Amtrak train...The specific structures included in SKIPJACK have a long evaluation history, and the cryptographic properties of those structures had many prior years of intense study before the formal process began in 1987. — SKIPJACK Review, Interim Report, 19931993 is a common year starting on Friday and marked the Beginning of the International Decade to Combat Racism and Racial Discrimination (1993-2003 Events January January 1 Czechoslovakia divides. Establishment of independent Slovakia and Czech Republic..

2 Description

Skipjack uses an 80-bit key to encrypt 64-bitIn modern cryptography, symmetric key ciphers are generally divided into stream ciphers and block ciphers. Block ciphers operate on a fixed length string of bits. The length of this bit string is the block size . Both the input ( plaintext) and output ( c data blocks. It is an unbalanced Feistel network with 32 rounds.