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CBC-R [8] turns a decryption oracle into an encryption oracle, and is primarily demonstrated against padding oracles. Using padding oracle attack CBC-R can craft an initialization vector and ciphertext block for any plaintext: decrypt any ciphertext P i = PODecrypt( C i) XOR C i−1, select previous cipherblock C x−1 freely,
Also like CBC, decryption can be parallelized. CFB, OFB and CTR share two advantages over CBC mode: the block cipher is only ever used in the encrypting direction, and the message does not need to be padded to a multiple of the cipher block size (though ciphertext stealing can also be used for CBC mode to make padding unnecessary).
The attacker can then combine the oracle with a systematic search of the problem space to complete their attack. [1] The padding oracle attack, and compression oracle attacks such as BREACH, are examples of oracle attacks, as was the practice of "crib-dragging" in the cryptanalysis of the Enigma machine. An oracle need not be 100% accurate ...
For CBC ciphertext stealing, there is a clever (but opaque) method of implementing the described ciphertext stealing process using a standard CBC interface. Using this method imposes a performance penalty in the decryption stage of one extra block decryption operation over what would be necessary using a dedicated implementation.
It makes some of the plaintext structure visible in the ciphertext. Selecting other modes, such as using a sequential counter over the block prior to encryption (i.e., CTR mode) and removing it after decryption avoids this problem. Another mode, Cipher Block Chaining (CBC) is one of the most commonly used modes of AES due to its use in TLS. CBC ...
The oracle returns the bitwise exclusive-or of the key with the string of zeroes. The string returned by the oracle is the secret key. While the one-time pad is used as an example of an information-theoretically secure cryptosystem, this security only holds under security definitions weaker than CPA security. This is because under the formal ...
The challenger selects a bit b ∈ {0, 1} uniformly at random, and sends the "challenge" ciphertext C = E(PK, M b) back to the adversary. The adversary is free to perform any number of additional computations or encryptions. In the non-adaptive case (IND-CCA1), the adversary may not make further calls to the decryption oracle.
The term "lunchtime attack" refers to the idea that a user's computer, with the ability to decrypt, is available to an attacker while the user is out to lunch. This form of the attack was the first one commonly discussed: obviously, if the attacker has the ability to make adaptive chosen ciphertext queries, no encrypted message would be safe ...