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Represents the total number of possible values of keys in a cryptographic algorithm or other security measure, such as a password.
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A cryptanalysis success where the attacker discovers additional plain texts (or cipher texts) not previously known.

Question 195 - 212-81 discussion

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The mode makes a block cipher into a synchronous stream cipher. It generates keystream blocks, which are then XORed with the plaintext blocks to get the ciphertext.

A.
Cipher-block chaining (CBC)
Answers
A.
Cipher-block chaining (CBC)
B.
Electronic codebook (ECB)
Answers
B.
Electronic codebook (ECB)
C.
Output feedback (OFB)
Answers
C.
Output feedback (OFB)
D.
Cipher feedback (CFB)
Answers
D.
Cipher feedback (CFB)
Suggested answer: C

Explanation:

Output feedback (OFB)

https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Output_feedback_(OFB)

The output feedback (OFB) mode makes a block cipher into a synchronous stream cipher. It generates keystream blocks, which are then XORed with the plaintext blocks to get the ciphertext. Just as with other stream ciphers, flipping a bit in the ciphertext produces a flipped bit in the plaintext at the same location. This property allows many error-correcting codes to function normally even when applied before encryption.

Incorrect answers:

Cipher feedback (CFB)- mode, a close relative of CBC, makes a block cipher into a self-synchronizing stream cipher.

Electronic codebook (ECB)- the simplest of the encryption modes (named after conventional physical codebooks). The message is divided into blocks, and each block is encrypted separately.

Cipher-block chaining (CBC)- Ehrsam, Meyer, Smith and Tuchman invented the cipher block chaining (CBC) mode of operation in 1976. In CBC mode, each block of plaintext is XORed with the previous ciphertext block before being encrypted. This way, each ciphertext block depends on all plaintext blocks processed up to that point. To make each message unique, an initialization vector must be used in the first block.

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asked 18/09/2024
Jevgenij Žarikov
39 questions
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