Which of the following statements pertaining to block ciphers is incorrect?

Question

Options

• AIt operates on fixed-size blocks of plaintext.
• BIt is more suitable for software than hardware implementations.
• CPlain text is encrypted with a public key and decrypted with a private key.
• DSome Block ciphers can operate internally as a stream.

• A
  4% (2)
• B
  2% (1)
• C
  94% (44)

Explanation

Block ciphers do not use public cryptography (private and public keys). Block ciphers is a type of symmetric-key encryption algorithm that transforms a fixed-size block of plaintext (unencrypted text) data into a block of ciphertext (encrypted text) data of the same length. They are appropriate for software implementations and can operate internally as a stream. See more info below about DES in Output Feedback Mode (OFB), which makes use internally of a stream cipher. 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.

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