Ladder-DES

Ladder-DES

General
Designers	Terry Ritter
First published	February 22, 1994
Derived from	DES
Related to	DEAL
Cipher detail
Key sizes	224 bits
Block sizes	128 bits
Structure	Nested Feistel network
Rounds	4
Best public cryptanalysis
Eli Biham's attacks require 236 plaintext-ciphertext pairs

In cryptography, Ladder-DES is a block cipher designed in 1994 by Terry Ritter. It is a 4-round Feistel cipher with a block size of 128 bits, using DES as the round function. It has no actual key schedule, so the total key size is 4×56=224 bits.

In 1997, Eli Biham found two forms of cryptanalysis for Ladder-DES that depend on the birthday paradox; the key is deduced from the presence or absence of collisions, plaintexts that give equal intermediate values in the encryption process. He presented both a chosen-plaintext attack and a known-plaintext attack; each uses about 2³⁶ plaintexts and 2⁹⁰ work, but the known-plaintext attack requires much more memory.

References

• Terry Ritter (22 February 1994). "Ladder DES". Newsgroup: sci.crypt. Usenet: 1994Feb22.083353.26012@cactus.org. Retrieved 30 January 2007.
• Eli Biham (1997). Cryptanalysis of Ladder-DES (PDF). 4th International Workshop on Fast Software Encryption (FSE '97). Haifa: Springer-Verlag. pp. 134–138. Retrieved 30 January 2007.