Samiksha Jaiswal (Editor)

Residual block termination

Updated on
Edit
Like
Comment
Share on FacebookTweet on TwitterShare on LinkedInShare on Reddit

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

Contents

Encryption procedure

If the plaintext length N is not a multiple of the block size L:

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

    • Decryption procedure

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

    • Short message

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

    References

    Residual block termination Wikipedia
    (Text) CC BY-SA


    Similar Topics