Cryptography Reference
In-Depth Information
Primitive root A number g is the primitive root modulo of a prime number, p ,
if the p
1 numbers, g 0 ,g 1 ,...,g p 2 , produce all possible p
1 remainders,
1 , 2 ,...,p
1, when divided by p . In other words, the number-theoretical equa-
tion y g x (mod p) can always be solved in x for each y that differs from 0
( x is the discrete logarithm of y to base g) . Primitive roots are required in asym-
metric methods that are based on the discrete logarithm, e.g., the Diffie - Hellman
congruence (see Section 6.1.1).
Private key A secret key known only to its creator and used in asymmetric encryption
methods, where it can also be used for decryption, as opposed to the public key.
Probabilistic method A special asymmetric method, where many public keys belong
to one private key. A well-known representative is the method by Blum, Blum,
and Shub (see Section 5.8).
Probable word A character string that is assumed to occur in a plaintext (often a
specific word). Pattern search or negative pattern search can be used to find the
position of a probable word, which means that a plaintext attack was successful.
Probable words are relevant mainly in classic cryptanalysis (see Section 3.4.1, for
example).
Product algorithm A special block algorithm, where the same key-dependent encryp-
tion function is applied to a block several times in a row. The use of this function
is referred to as a round , and round's keys are derived from that key. The encryp-
tion function is applied in every round, depending on the pertaining round's key
(see Section 4.1.4).
Public key A publicly known key used in asymmetric encryption methods; it is used
only for encryption.
Public-key method See 'asymmetric encryption'.
Quantum computer To date, a hypothetical computer that works by the laws of
quantum mechanics. If quantum computers existed, they could be used to quickly
break all currently secure public-key methods (see Section 5.9).
Quantum cryptography A field involving physics and cryptographic protocols that
enables you to safely prove an eavesdropping attempt. Quantum cryptography
enables secure exchange of information (e.g., key exchange), but it is extraor-
dinarily hard to implement in practice and, if achieved, considered a technical
masterpiece (see Section 5.8).
RC4 A fast encryption method that is very easy to program and apparently secure to
date. It is a stream cipher (see Section 5.6).
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