AES Cipher Block Chaining 128 bit message I understand that for AES CBC you need to split the plaintext up into blocks and perform XOR'ing using the previous blocks calculations etc. 

However, if your message is exactly 128 bits long, do you only perform the XOR with the IV and the encryption with the key once? Or is there a way to split up a 128 bit message so that you can perform the cipher block chaining method as intended.

Thanks.
However, if your message is exactly 128 bits long, do you only perform the XOR with the IV and the encryption with the key once? Or is there a way to split up a 128 bit message so that you can perform the cipher block chaining method as intended.


This is a non-starter, as there is nothing wrong with performing a single block encrypt in CBC mode. For 128 bits messages you don't need any padding method, even for CBC mode, but generally we try and apply PKCS#7 padding for compatibility reasons.

The XOR of the unpredictable IV with the plaintext is required, otherwise your cipher would not be able to handle identical messages without leaking information. If your 128 bit messages are unique by itself they you could just use a single block encrypt of the block cipher (the attacker would only know that no repetition is present in the messages).