I would like to encrypt some authentication tokens using AES 256 (not tied to this algorithm but it seems to be a reasonable choice). These messages are usually very short at 128-256 bits. I'm concerned foremost about the security, not very concerned about ciphertext length or performance in either encryption or decryption. These are shared secrets so I have to be able to obtain the plaintext.
I am curious if any additional padding beyond what is required for the message to match the blocksize is beneficial.
To clarify this is not a question about padding the message so that it can be run through the encryption algorithm, but rather would I gain anything by padding to the message to say 1024 bits vs. 256 when the message is very short. I am already using an IV as I am reusing a key.
If I do pad to an additional length should I just use a single character, or should I put in a random stream of data?
My concern is that by only padding to 256 bits I may potentially betray the size of the secret (although most of them are shorter then the blocksize).