Write down the difference between block cipher and stream cipher.
Subject Computer and Network Security
NU Year Set: 2.(c) Marks: 4 Year: 2013
  1. Block cipher technique involves encryption of one block of text at a time, i.e. singly. Similarly, decrypt the text by taking one block after another. In contrast, Stream cipher technique involves encryption and decryption of one byte of the text at a time.
  2. Block cipher uses both confusion and diffusion while stream cipher relies only on confusion.
  3. The usual size of the block could be 64 or 128 bits in the Block cipher. As against, 1 byte (8 bits) at a time is converted in the stream cipher.
  4. Block cipher uses ECB (Electronic Code Book) and CBC (Cipher Block Chaining) algorithm modes. On the contrary, Stream cipher uses CFB (Cipher Feedback) and OFB (Output Feedback) algorithm modes.
  5. Stream cipher uses XOR function for converting the plain text into cipher text, that is the reason why it is easy to reverse the XORed bits. Whereas Block cipher does not use XOR for doing so.
  6. Block cipher uses the same key to encrypt each block while stream cipher uses a different key for each byte.
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