Glossary - Cryptology Unlocked - page 494

generally used method is the HMAC checksum (see [MenOoVan, 9.5.2]). MACs
are used in tamperproof checksums (e.g., as a defense against viruses), but also
in certain protocols for digital money (MilliCent).
MARS IBM's proposal for the AES challenge; it is very secure, effective, and fast,
like all five final AES candidates.
MD2, MD4, MD5 Three important one-way hash functions (see Section 6.3.1).
Multiple encryption The repeated encryption of a text using the same or different
encryption algorithms. In most cases, this is believed to increase the security, but
cryptanalysis doesn't seem to have made much progress in this field (at least in
public research). The best known example of multiple encryption is Triple-DES
(see Section 5.2.1).
NBS (National Bureau of Standards) Former name of the NIST.
Negative pattern search Some encryption methods (e.g., Enigma, ciphering cylinders)
do not transform any character onto itself. This helps exclude certain patterns that
could be exploited in the plaintext (see Section 3.4.1). It is important in classic
(character-oriented) cryptology, but not significant for current algorithms due to
the avalanche effect.
N-hash A cryptographically insecure one-way hash function (see Section 6.3.1).
NIST (National Institute of Standards and Technology) A Department of the US Sec-
retary of Commerce which, among other things, specifies cryptographic standards
(including DES, EES, and DSS). Cooperates closely with the NSA.
NSA (National Security Agency) A US authority dealing intensively with cryptology
and worldwide surveillance. Estimated to employ 40 000 people (including at least
2000 mathematicians); disposes of extremely fast computation technology (being
the single largest buyer of hardware in the world), and also produces computers
itself. Though the NSA was founded by Truman in 1952, its existence became
publicly known in connection with the development of DES in the early 1970s.
OFB (Output Feedback Mode) A ciphering mode used in block algorithms (see
Section 5.1.1).
One-time pad A random byte or bit sequence that is at least as long as the plaintext.
Encryption and decryption are done by simple XORing with the plaintext or
ciphertext, respectively. One-time pads are currently the only method with proven
security (Section 2.6).