Another trivial question: gcry_cipher_encrypt() (plaintext length)

[Jules Colding]

Hi,

Once more I'm demonstrating my utter lack of knowledge in all matters
related to cryptography. Please forgive these trivial questions.

I'm trying to use gcry_cipher_encrypt(). I've set the cipher mode to
GCRY_CIPHER_MODE_CFB(*) and the algorithm is GCRY_CIPHER_AES256.

My problem is that the size of the plaintext data is unknown to me as I
have to use gcry_cipher_encrypt() for arbitrary plaintext data.

The manual for libgcrypt says that the size of the input data has to be
a multiple of the block size of the cipher algorithm. 

So what I'm really asking about is whether there is a standard way of
padding the input data to achieve the required size? How do I
remove/recognize the padding when decrypting?

Thanks a lot in advance,
  jules


(*) Is that mode a wise choice?