Glossary - Cryptology Unlocked - page 488

Authentication A cryptologically secure method to verify the originator of a message,
trying to prevent the sender from pretending to be somebody else. For example,
by keying in a PIN at an ATM, the ATM authenticates the customer, because only
he is assumed to know the PIN to an account. The receiver of a message identifies
the sender, whereas the sender authenticates himself (proving his identity).
Avalanche effect Particularly strong diffusion of a block algorithm: every changed
bit of the plaintext block should change every bit of the ciphertext block. If
the probability of changing a ciphertext bit deviates from 50 %, then this is a
vulnerability differential cryptanalysis could exploit (see Section 4.4.2).
Bletchley Park A strictly fenced-off area in Great Britain, where during World War
II, encrypted messages of the German Wehrmacht were decrypted in masses,
especially from the Enigma. At the beginning of 1944, about 7000 people worked
at the Park, decrypting up to 90 000 messages per month (see Section 2.5.2).
Block, block algorithm A plaintext or ciphertext section that is encrypted or decrypted
as a whole. Algorithms that encrypt only blockwise are called block algorithms
(see 'stream cipher').
Blowfish A block algorithm developed by Bruce Schneier, which can be freely used;
it is thought to be secure to date (see Section 5.7.4).
Breaking a method Using an approach to decrypt messages encrypted with a given
encryption method without knowing the secret key. A method is deemed not to
have been broken if it resists the most effective attack known by trial-and-error
testing all possible keys (see 'brute force').
Brute force Trial-and-error testing all possible keys to reveal a plaintext. With 40-bit
keys (e.g., in the international version of Netscape Navigator), brute force takes
several computation hours on an extremely fast general-purpose computer (depend-
ing on the algorithm and the type of test). 56-bit keys (DES) require special
hardware, such as the Deep Crack computer (see Section 4.4.1). In contrast, 80-bit
keys (Skipjack) are secure into the near future. Brute force is basically impossible
against 128-bit keys (IDEA) with the current technology. (One billion computers
working in parallel, doing one billion decryptions per second each, would take
ten million years; see Section 5.9.)
BSD Important UNIX variant, mostly popular in academic fields (representatives
include SunOS and Free BSD). Large parts of it were integrated in SystemV.4
(see 'System V').
Caesar cipher Probably the simplest ciphering method (Section 2.1); no longer used.