Key recovery attack

A key-recovery attack is an adversary's attempt to recover the cryptographic key of an encryption scheme. 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 2 128 or greater, making such attacks infeasible with current technology.