I'm currently implementing, with
crypto++, and AES tranmsission system, whose
key is based on a previous
MasterSecret of 256 bits (which has been expanded using PBKDF2).
MasterSecret is then split into a
key and an
iv, to encrypt a message using
I must work with AES-256, so my key must be 256-bit long. The iv for GCM is always 128-bit long.
So, briefly, I must extract from a 256-bit
MasterSecret a 256-bit key and a 128-bit IV.
How to do it ?
I thought of taking the
MasterSecret as the key, and then hashing the key to get then the iv of the desired length.
Is there a more efficient/elegant way to obtain 384 bits from a 256 bit