The BEAR and LION
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 ...
s were invented by
Ross Anderson and
Eli Biham
Eli Biham ( he, אלי ביהם) is an Israeli cryptographer and cryptanalyst, currently a professor at the Technion - Israel Institute of Technology Computer Science department. Starting from October 2008 and till 2013, Biham was the dean of t ...
by combining a
stream cipher
stream cipher is a symmetric key cipher where plaintext digits are combined with a pseudorandom cipher digit stream (keystream). In a stream cipher, each plaintext digit is encrypted one at a time with the corresponding digit of the keystream ...
and a
cryptographic hash function
A cryptographic hash function (CHF) is a hash algorithm (a map of an arbitrary binary string to a binary string with fixed size of n bits) that has special properties desirable for cryptography:
* the probability of a particular n-bit output re ...
. The algorithms use a very large variable
block size, on the order of 2
13 to 2
23 bits . Both are 3-round generalized (alternating)
Feistel cipher
In cryptography, a Feistel cipher (also known as Luby–Rackoff block cipher) is a symmetric structure used in the construction of block ciphers, named after the German-born physicist and cryptographer Horst Feistel, who did pioneering research ...
s,
using the hash function and the stream cipher as round functions. BEAR uses the hash function twice with independent
keys, and the stream cipher once. LION uses the stream cipher twice and the hash function once. The inventors proved that an attack on either BEAR or LION that recovers the key would break both the stream cipher and the hash.
References
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Feistel ciphers
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