Hello,

often you find products which implement AES 256Bit encryption e.g. in
hard drive encryption, file encryption or whatever. The user specifies a
password/passphrase which is used for encryption.

My actual question is what does the standard say to passwords which are
not exactly 256 Bit long? Often user passwords are 8 characters long
(which means an effective key size of 64 Bit). Or someone could have a
key file which is 300 Bit long. But AES with 256 Bit support would only
use 256 Bit of the 300 Bit. Or it has to calculate a 256 Bit key of the
64 Bit material specified from the user.

How to calculate a key of size 256 Bit which is standard compliant. Is
there even a library outside which does this for me (e.g. OpenSSL uses
MD5 digests sometimes)?

I just want to develop an application where a user can specify a
password to encrypt something in AES 256 Bit. But the encryption library
I use forces me to specify a key with the exact 256 Bit. So I have to
calculate a key which is standard compliant.

Does someone has an idea, hint?

Best regards
Stefan

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