Residual block termination

In cryptography, residual block termination is a variation of mode (CBC) that does not require any . It does this by effectively changing to mode for one block. The cost is the increased complexity.

Contents

Encryption procedure

If the length N is not a multiple of the L:

  • Encrypt the ⌊N/L⌋ full blocks of plaintext using the ;
  • Encrypt the last full encrypted block again;
  • the remaining bits of the plaintext with leftmost bits of the re-encrypted block.

Decryption procedure

  • the ⌊N/L⌋ full encrypted blocks using the Cipher Block Chaining mode;
  • Encrypt the last full encrypted block;
  • the remaining bits of the ciphertext with leftmost bits of the re-encrypted block.

Short message

For messages shorter than one , residual block termination can use an encrypted instead of the previously encrypted block.

Source

http://wikipedia.org/

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