Attack model

In cryptanalysis, attack models or attack types are a classification of cryptographic attacks specifying the kind of access a cryptanalyst has to a system under attack when attempting to "break" an encrypted message (also known as ciphertext) generated by the system. The more elaborate the access the cryptanalyst can gain, the more useful information it can extracted and utilize for breaking the system.

In cryptography, a sending party uses a cipher to encrypt (transform) a secret plaintext into a ciphertext, which is sent over an insecure communication channel to the receiving party. The receiving party uses an inverse cipher to decrypt the ciphertext to obtain the plaintext. A secret knowledge is required to apply the inverse cipher to the ciphertext. This secret knowledge is usually a short number or string called a key. In a cryptographic attack a third party cryptanalyst analyzes the ciphertext to try to "break" the cipher, to read the plaintext and obtain the key so that future enciphered messages can be read. It is usually assumed that the encryption and decryption algorithms themselves are public knowledge and available to the cryptographer, as this is the case for modern ciphers which are published openly. This assumption is called Kerckhoffs's principle.