Editing Ciphertext stealing (section)

====CBC encryption steps====
# ''X''<sub>''n''−1</sub> = ''P''<sub>''n''−1</sub> XOR ''C''<sub>''n''−2</sub>.  Exclusive-OR ''P''<sub>''n''−1</sub> with the previous ciphertext block, ''C''<sub>''n''−2</sub>, to create ''X''<sub>''n''−1</sub>.  This is equivalent to the behavior of standard CBC mode.
# ''E''<sub>''n''−1</sub> = Encrypt (''K'', ''X''<sub>''n''−1</sub>).  Encrypt ''X''<sub>''n''−1</sub> to create ''E''<sub>''n''−1</sub>.   This is equivalent to the behavior of standard CBC mode.
# ''C''<sub>''n''</sub> = Head (''E''<sub>''n''−1</sub>, ''M''). Select the first ''M'' bits of ''E''<sub>''n''−1</sub> to create ''C''<sub>''n''</sub>.  The final ciphertext block, ''C''<sub>''n''</sub>, is composed of the leading ''M'' bits of the second-to-last ciphertext block.  In all cases, the last two blocks are sent in a different order than the corresponding plaintext blocks.
# ''P'' = ''P''<sub>''n''</sub> || 0<sup>''B''−''M''</sup>.  Pad ''P''<sub>''n''</sub> with zeros at the end to create ''P'' of length ''B''.  The zero padding in this step is important for step 5.
# ''D''<sub>''n''</sub> = ''E''<sub>''n''−1</sub> XOR ''P''.  Exclusive-OR ''E''<sub>''n''−1</sub> with ''P'' to create ''D''<sub>''n''</sub>.  For the first ''M'' bits of the block, this is equivalent to CBC mode; the first ''M'' bits of the previous block's ciphertext, ''E''<sub>''n''−1</sub>, are XORed with the ''M'' bits of  plaintext of the last plaintext block.  The zero padding of ''P'' in step 4 was important, because it makes the XOR operation's effect on the last ''B''−''M'' bits equivalent to copying the last ''B''−''M'' bits of ''E''<sub>''n''−1</sub> to the end of ''D''<sub>''n''</sub>.  These are the same bits that were  stripped off of ''E''<sub>''n''−1</sub> in step 3 when ''C''<sub>''n''</sub> was created.
# ''C''<sub>''n''−1</sub> = Encrypt (''K'', ''D''<sub>''n''</sub>).  Encrypt ''D''<sub>''n''</sub> to create ''C''<sub>''n''−1</sub>.  For the first ''M'' bits, this is equivalent to what would happen in CBC mode (other than the ciphertext ordering).  For the last ''B''−''M'' bits, this is the second time that these data have been encrypted under this key (It was already encrypted in the production of ''E''<sub>''n''−1</sub> in step 2).