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Known-key distinguishing attack

In cryptography, a known-key distinguishing attack is an attack model against symmetric ciphers, whereby an attacker who knows the key can find a structural property in cipher, where the transformation from plaintext to ciphertext is not random. There is no common formal definition for what such a transformation may be. The chosen-key distinguishing attack is strongly related, where the attacker can choose a key to introduce such transformations.[1]

These attacks do not directly compromise the confidentiality of ciphers, because in a classical scenario, the key is unknown to the attacker. Known-/chosen-key distinguishing attacks apply in the "open key model" instead.[1] They are known to be applicable in some situations where block ciphers are converted to hash functions, leading to practical collision attacks against the hash.[2]

Known-key distinguishing attacks were first introduced in 2007 by Lars Knudsen and Vincent Rijmen[1] in a paper that proposed such an attack against 7 out of 10 rounds of the AES cipher and another attack against a generalized Feistel cipher. Their attack finds plaintext/ciphertext pairs for a cipher with a known key, where the input and output have s least significant bits set to zero, in less than 2s time (where s is fewer than half the block size).[3]

These attacks have also been applied to reduced-round Threefish (Skein)[4][5] and Phelix.[6]

See also


  1. ^ a b c Elena Andreeva, Andrey Bogdanov, Bart Mennink (8 July 2014). Towards Understanding the Known-Key Security of Block Ciphers. FSE 2014. 
  2. ^ Yu Sasaki, Kan Yasuda (2011). Known-Key Distinguishers on 11-Round Feistel and Collision Attacks on Its Hashing Modes (PDF). FSE 2011. 
  3. ^ Lars Knudsen, Vincent Rijmen (2007). Known-Key Distinguishers for Some Block Ciphers (PDF). Asiacrypt 2007. 
  4. ^ Bruce Schneier (1 September 2010). "More Skein News". Schneier on Security. 
  5. ^ Dmitry Khovratovich; Ivica Nikolic; Christian Rechberger (20 October 2010). "Rotational Rebound Attacks on Reduced Skein". 
  6. ^ Yaser Esmaeili Salehani, Hadi Ahmadi (2006). "A Chosen-key Distinguishing Attack on Phelix". 

Further reading