Nimbus (cipher)

This article is about the block cipher. For other uses, see Nimbus (disambiguation).

In cryptography, Nimbus is a block cipher invented by Alexis Machado in 2000. It was submitted to the NESSIE project, but was not selected.

Nimbus

General
Designers	Alexis Machado
First published	2000
Cipher detail
Key sizes	128 bits
Block sizes	64 bits
Rounds	5
Best public cryptanalysis
Differential cryptanalysis can break Nimbus with 256 chosen plaintexts.

The algorithm uses a 128-bit key. It operates on blocks of 64 bits and consists of 5 rounds of encryption. The round function is exceedingly simple. In each round the block is XORed with a subkey, the order of its bits is reversed, and then it is multiplied mod 2⁶⁴ by another subkey, which is forced to be odd.^[1]

Nimbus was broken by Vladimir Furman; he found a differential attack using only 256 chosen plaintexts.^[2]