Another trivial question: gcry_cipher_encrypt() (plaintext length)

Jules Colding colding at
Tue Apr 24 12:14:09 CEST 2007


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,

(*) Is that mode a wise choice?

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