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.