Editing Ciphertext stealing (section)

====CBC decryption steps====
# ''D''<sub>''n''</sub> = Decrypt (''K'', ''C''<sub>''n''−1</sub>).  Decrypt ''C''<sub>''n''−1</sub> to create ''D''<sub>''n''</sub>.  This undoes step 6 of the encryption process.
# ''C'' = ''C''<sub>''n''</sub> || 0<sup>''B''−''M''</sup>.  Pad ''C''<sub>''n''</sub> with zeros at the end to create a block ''C'' of length ''B''.  We are padding ''C''<sub>''n''</sub> with zeros to help in step 3.
# ''X''<sub>''n''</sub> = ''D''<sub>''n''</sub> XOR ''C''.  Exclusive-OR ''D''<sub>''n''</sub> with ''C'' to create ''X''<sub>''n''</sub>.  Looking at the first ''M'' bits, this step has the result of XORing ''C''<sub>''n''</sub> (the first ''M'' bits of the encryption process' ''E''<sub>''n''−1</sub>) with the (now decrypted) ''P''<sub>''n''</sub> XOR Head (''E''<sub>''n''−1</sub>, ''M'') (see steps 4-5 of the encryption process).  In other words, we have CBC decrypted the first ''M'' bits of ''P''<sub>''n''</sub>.  Looking at the last ''B''−''M'' bits, this recovers the last ''B''−''M'' bits of ''E''<sub>''n''−1</sub>.
# ''P''<sub>''n''</sub> = Head (''X''<sub>''n''</sub>, ''M'').  Select the first ''M'' bits of ''X''<sub>''n''</sub> to create ''P''<sub>''n''</sub>.  As described in step 3, the first ''M'' bits of ''X''<sub>''n''</sub> contain ''P''<sub>''n''</sub>.  We queue this last (possibly partial) block for eventual output.
# ''E''<sub>''n''−1</sub> = ''C''<sub>''n''</sub> || Tail (''X''<sub>''n''</sub>, ''B''−''M'').  Append the tail (''B''−''M'') bits of ''X''<sub>''n''</sub> to ''C''<sub>''n''</sub> to create ''E''<sub>''n''−1</sub>.  As described in step 3, ''E''<sub>''n''−1</sub> is composed of  all of ''C''<sub>''n''</sub> (which is ''M'' bits long) appended with the last ''B''−''M'' bits of ''X''<sub>''n''</sub>.  We reassemble ''E''<sub>''n''−1</sub> (which is the same ''E''<sub>''n''−1</sub> seen in the encryption process) for processing in step 6.
# ''X''<sub>''n''−1</sub> = Decrypt (''K'', ''E''<sub>''n''−1</sub>).  Decrypt ''E''<sub>''n''−1</sub> to create ''X''<sub>''n''−1</sub>.  This reverses encryption step 2.  ''X''<sub>''n''−1</sub> is the same as in the encryption process.
# ''P''<sub>''n''−1</sub> = ''X''<sub>''n''−1</sub> XOR ''C''<sub>''n''−2</sub>.  Exclusive-OR ''X''<sub>''n''−1</sub> with the previous ciphertext block, ''C''<sub>''n''−2</sub>, to create ''P''<sub>''n''−1</sub>.  Finally, we reverse the XOR step from step 1 of the encryption process.