Editing Adaptive chosen-ciphertext attack (section)

{{Short description|Cryptographic attack}}
{{More footnotes needed|date=January 2011}}
An '''adaptive chosen-ciphertext attack''' (abbreviated as '''CCA2''') is an interactive form of [[chosen-ciphertext attack]] in which an attacker first sends a number of [[ciphertext]]s to be decrypted chosen adaptively, and then uses the results to distinguish a target ciphertext without consulting the oracle on the challenge ciphertext. In an adaptive attack, the attacker is further allowed adaptive queries to be asked after the target is revealed (but the target query is disallowed). It is extending the [[chosen-ciphertext attack|indifferent (non-adaptive) chosen-ciphertext attack]] (CCA1) where the second stage of adaptive queries is not allowed. [[Charles Rackoff]] and Dan Simon defined CCA2 and suggested a system building on the non-adaptive CCA1 definition and system of [[Moni Naor]] and [[Moti Yung]] (which was the first treatment of chosen ciphertext attack immunity of public key systems).

In certain practical settings, the goal of this attack is to gradually reveal information about an encrypted message, or about the decryption key itself. For [[public-key cryptography|public-key systems]], adaptive-chosen-ciphertexts are generally applicable only when they have the property of [[malleability (cryptography)|ciphertext malleability]] &mdash; that is, a ciphertext can be modified in specific ways that will have a predictable effect on the decryption of that message.