Concept

Déni plausible (cryptologie)

Résumé
In cryptography and steganography, plausibly deniable encryption describes encryption techniques where the existence of an encrypted file or message is deniable in the sense that an adversary cannot prove that the plaintext data exists. The users may convincingly deny that a given piece of data is encrypted, or that they are able to decrypt a given piece of encrypted data, or that some specific encrypted data exists. Such denials may or may not be genuine. For example, it may be impossible to prove that the data is encrypted without the cooperation of the users. If the data is encrypted, the users genuinely may not be able to decrypt it. Deniable encryption serves to undermine an attacker's confidence either that data is encrypted, or that the person in possession of it can decrypt it and provide the associated plaintext. Deniable encryption makes it impossible to prove the existence of the plaintext message without the proper decryption key. This may be done by allowing an encrypted message to be decrypted to different sensible plaintexts, depending on the key used. This allows the sender to have plausible deniability if compelled to give up their encryption key. The notion of "deniable encryption" was used by Julian Assange and Ralf Weinmann in the and explored in detail in a paper by Ran Canetti, Cynthia Dwork, Moni Naor, and Rafail Ostrovsky in 1996. Deniable encryption allows the sender of an encrypted message to deny sending that message. This requires a trusted third party. A possible scenario works like this: Bob suspects his wife Alice is engaged in adultery. That being the case, Alice wants to communicate with her secret lover Carl. She creates two keys, one intended to be kept secret, the other intended to be sacrificed. She passes the secret key (or both) to Carl. Alice constructs an innocuous message M1 for Carl (intended to be revealed to Bob in case of discovery) and an incriminating love letter M2 to Carl. She constructs a cipher-text C out of both messages, M1 and M2, and emails it to Carl.
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