Skipjack
Published:
June 1998
References:
- [Def] U.S. National Institute of Standards and Technology,
- SKIPJACK and KEA Specifications
- "Observations on the SkipJack Encryption Algorithm,"
- "Cryptanalysis of Skipjack Reduced to 31 Rounds using Impossible Differentials,"
- "Truncated differentials and Skipjack,"
- Proceedings of CRYPTO '99.
- Key length: 80 bits.
- Block size: 8 bytes.
Security comment:
The "Observations on the SkipJack Encryption Algorithm" pages cited above describe the following attack, among others:
This note summarizes our first week of analysis. The main result is an attack on a variant, which we call SkipJack-3XOR (SkipJack minus 3 XORs). The only difference between SkipJack and SkipJack-3XOR is the removal of 3 out of the 320 XOR operations. The attack uses the ciphertexts derived from about 500 plaintexts which are identical except for the second 16 bit word. Its total running time is equivalent to about one million SkipJack encryptions, which can be carried out in seconds on a personal computer.
This is still a preliminary result, but it reiterates our earlier comment that SkipJack does not have a conservative design with a large margin of safety. |
