A key-recovery attack is an adversary's attempt to recover the
cryptographic key
A key in cryptography is a piece of information, usually a string of numbers or letters that are stored in a file, which, when processed through a cryptographic algorithm, can encode or decode cryptographic data. Based on the used method, the key c ...
of an encryption scheme. Normally this means that the attacker has a pair, or more than one pair, of
plaintext
In cryptography, plaintext usually means unencrypted information pending input into cryptographic algorithms, usually encryption algorithms. This usually refers to data that is transmitted or stored unencrypted.
Overview
With the advent of comp ...
message and the corresponding
ciphertext
In cryptography, ciphertext or cyphertext is the result of encryption performed on plaintext using an algorithm, called a cipher. Ciphertext is also known as encrypted or encoded information because it contains a form of the original plaintext ...
.
[ Goldwasser, S. and Bellare, M.br>"Lecture Notes on Cryptography"]
Summer course on cryptography, MIT, 1996-2001 Historically, cryptanalysis of block ciphers has focused on key-recovery, but security against these sorts of attacks is a very weak guarantee since it may not be necessary to recover the key to obtain partial information about the message or decrypt message entirely.
Modern cryptography uses more robust notions of security. Recently,
indistinguishability under adaptive chosen-ciphertext attack (IND-CCA2 security) has become the "golden standard" of security. The most obvious key-recovery attack is the
exhaustive key-search attack. But modern ciphers often have a key space of size
or greater, making such attacks infeasible with current technology.
KR advantage
In
cryptography
Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or ''-logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adver ...
, the key-recovery advantage (KR advantage) of a particular
algorithm
In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific Computational problem, problems or to perform a computation. Algorithms are used as specificat ...
is a measure of how effective an algorithm can mount a key-recovery attack. Consequently, the maximum key-recovery advantage attainable by any algorithm with a fixed amount of
computational resources
In computational complexity theory, a computational resource is a resource used by some computational models in the solution of computational problems.
The simplest computational resources are computation time, the number of steps necessary to s ...
is a measure of how difficult it is to recover a
cipher's key. It is defined as the probability that the adversary algorithm can guess a cipher's randomly selected key, given a fixed amount of computational resources.
[ Goldwasser, S. and Bellare, M]
"Lecture Notes on Cryptography"
Summer course on cryptography, MIT, 1996-2001 An extremely low KR advantage is essential for an encryption scheme's
security
Security is protection from, or resilience against, potential harm (or other unwanted coercive change) caused by others, by restraining the freedom of others to act. Beneficiaries (technically referents) of security may be of persons and social ...
.
References
External links
cseweb.ucsd.edu paper MIT Lecture Notes on Cryptography
Cryptographic attacks
Theory of cryptography
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