Attack model

Attack models or attack types specify how much information a cryptanalyst has access to when breaking or cracking an encrypted message, commonly known as codebreaking or cracking the code. Some common attack models are:

Ciphertext-only attack
Known-plaintext attack
Chosen-plaintext attack
Chosen-ciphertext attack
Adaptive chosen-ciphertext attack
Indifferent chosen-ciphertext attack
The ciphertext-only attack model is the weakest because it implies that the cryptanalyst has just the encoded message.

Different attack models are used for other cryptographic systems, or more generally for all kind of security systems. Examples for such attack models are:
Adaptive chosen-message attack for digital signatures

References
 Information Security Laboratory  (powerpoint)

Other websites
University of Colorado at Boulder's introduction to Cryptography and attack models  (PDF)
University of Waterloo paper that discusses attack models (Postscript file) html version

Category:Cryptography