About
Ciphertext stealing (CTS) is a padding method in which the required padding bits are “stolen” from the penultimate ciphertext block.
It works without padding the message to a multiple of the block size, so the ciphertext is the same size as the plaintext.
The processing of all but the last two blocks is unchanged, but a portion of the second-last block's ciphertext is stolen to pad the last plaintext block.