Which of the following types of ciphers operates on a group of bits rather than an individual character or bit of a message?

Question

Options

• ABlock cipher
• BClassical cipher
• CSubstitution cipher
• DStream cipher

• A
  88% (22)
• B
  4% (1)
• C
  8% (2)

Explanation

Block ciphers encrypt data in fixed-size chunks (commonly 64 or 128 bits at a time), making option A correct - the defining characteristic is operating on a group of bits as a unit. Stream ciphers (D) are the close alternative, but they operate on individual bits or bytes one at a time, making them the opposite. Classical ciphers (B) are historical techniques (like Caesar cipher) that typically work on individual characters, not bit groups. Substitution ciphers (C) are a category of classical cipher that replace individual characters with other characters - also character-level, not group-level.

Memory tip: Think "block = bulk" - a block cipher processes a whole block of bits at once, like encrypting a whole chunk of data in one operation, whereas a stream cipher flows bit by bit like water through a pipe.

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