  BEAR, LION and LIONESS are block ciphers presented by Biham and Anderson
(1996), inspired by the famous Luby-Rackoff constructions of block ciphers from
other cryptographic primitives (1988). The ciphers proposed by Biham and
Anderson are based on one stream cipher and one hash function. Good properties
of the primitives ensure good properties of the block cipher. In particular,
they are able to prove that their ciphers are immune to any efficient
known-plaintext key-recovery attack that can use as input only one
plaintext-ciphertext pair. Our contribution is showing that these ciphers are
actually immune to any efficient known-plaintext key-recovery attack that can
use as input any number of plaintext-ciphertext pairs. We are able to get this
improvement by using slightly weaker hypotheses on the primitives. We also
discuss the attack by Morin (1996).
