Akelarre is a
block cipher
In cryptography, a block cipher is a deterministic algorithm operating on fixed-length groups of bits, called ''blocks''. Block ciphers are specified cryptographic primitive, elementary components in the design of many cryptographic protocols and ...
proposed in 1996, combining the basic design of
IDEA with ideas from
RC5
In cryptography, RC5 is a symmetric-key block cipher notable for its simplicity. Designed by Ronald Rivest in 1994, ''RC'' stands for "Rivest Cipher", or alternatively, "Ron's Code" (compare RC2 and RC4). The Advanced Encryption Standard (AES) c ...
. It was shown to be susceptible to a
ciphertext-only attack in 1997.
Akelarre is a 128-bit block cipher with a variable key-length which must be some multiple of 64 bits. The number of rounds is variable, but four are suggested. The round function of Akelarre is similar to IDEA in structure.
After the successful cryptanalysis of Akelarre, its designers responded with an updated variant called Ake98. This cipher differs from the original Akelarre in the new ''AR-box'' (addition–rotation box), the swapping of words at the end of a round, and the addition of subkeys at the beginning of each round. In 2004,
Jorge Nakahara, Jr. and Daniel Santana de Freitas found large classes of
weak keys for Ake98. These weak keys allow a cryptanalysis faster than exhaustive search using only 71 known plaintexts, for up to 11.5 rounds of Ake98.
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{{Cryptography navbox , block
Broken block ciphers