$6.$ Padding may not always be appropriate. For example, one might wish to store the encrypted data in the same memory buffer that originally contained the plaintext. In that case, the ciphertext must be the same length as the original plaintext. A mode for that purpose is the ciphertext stealing $($CTS$)$ mode. Figure $20\mathrm{.}12$a on pg$.633$ in CSPaP shows an implementation of this mode.