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Glossary of Terms (Page 5)

lattice - A lattice can be viewed as an N-dimensional grid.

LEAF - Law Enforcement Agency Field a component in the Clipper Chip.

life cycle - The length of time a key can be kept in use and still provide an appropriate level of security.

linear complexity - Referring to a sequence of 0's and 1's, the size of the smallest linear feedback shift register (LFSR) that would replicate the sequence. See also linear feedback shift register.

linear cryptanalysis - A known plaintext attack that uses linear approximations to describe the behavior of the block cipher. See known plaintext attack.

linear keyspace - A key space where each key is equally strong.

LFSR - linear feedback shift register. Used in many keystream generators because of its ability to produce sequences with certain desirable properties.

MAC - See message authentication code.

meet-in-the-middle attack - A known plaintext attack against double encryption with two separated keys where the attacker encrypts a plaintext with a key and "decrypts" the original ciphertext with another key and hopes to get the same value.

Message Authentication Code (MAC) - A MAC is a function that takes a variable length input and a key to produce a fixed-length output. See also hash-based MAC, stream-cipher based MAC, and block-cipher based MAC.

message digest - The result of applying a hash function to a message.

MHS - Message Handling System.

middle-person attack - A person who intercepts keys and impersonates the intended recipients.

MIME - Multipurpose Internet Mail Extensions.

MIPS - Millions of Instructions Per Second, a measurement of computing speed.

MIPS-Year - One year's worth of time on a MIPS machine.

mixed integer programming - The problem is to solve a linear programming problem where some of the variables are restricted to being integers.

modular arithmetic - a form of arithmetic where integers are considered equal if they leave the same remainder when divided by the modulus.

modulus - The integer used to divide out by in modular arithmetic.

multiple polynomial quadratic sieve (MPQS) - A variation of the quadratic sieve that sieves on multiple polynomials to find the desired relation. MQPS was used to factor RSA - 129.

NIST - National Institute of Standard and Technology, a United States agency that produces security and cryptography related standards (as well as others); these standards are published as FIPS documents.

non-repudiation - A property of a cryptosystem. Non-repudiation cryptosystems are those in which the users cannot deny actions they performed.

nonlinear keyspace - A key space comprised of strong and weak keys.

NSA - National Security Agency. A security-conscious U.S.government agency whose mission is to decipher and monitor foreign communications.

number field sieve - A method of factoring, currently the fastest general-purpose factoring algorithm published. It was used to factor RSA-130.

number theory - A branch of mathematics that investigates the relationships and properties of numbers.

OAEP - Optimal Asymmetric Encryption Padding; a provably secure way of encrypting a message.

one-time pad - A secret-key cipher in which the key is a truly random sequence of bits that is as long as the message itself, and encryption is performed by XORing the message with the key. This is theoretically unbreakable.

one-way function - A function that is easy to compute in one direction but quite difficult to reverse compute (compute in the opposite direction).

one-way hash function - A one-way function that takes a variable sized input and creates a fixed size output.