Hi,
I'm using AES-GCM to send multiple messages (CryptoPP::GCM<CryptoPP::AES>)
via AuthenticatedEncryptionFilter.
It seems I need to resynchronize the underlying GCM cipher after each
message with a call to Resynchronize which
needs a new iv as argument.
I see no reason why this new iv is neccessary. GCM uses a counter, so the
"iv" is a nonce, not necessitating
a fully random iv. Internally GCM increments the nonce for every AES block,
so at the point one has to resynchronize it,
it is already at a usefull last_iv+1.
Does anything break by extending CryptoPP::GCM by a resynchronize method
which does not change the iv, like:
class CtrNonceGCMEncryption : public CryptoPP::GCM<CryptoPP::AES >::
Encryption {
public:
void Resynchronize() { m_state = State_IVSet; }
};
and using this method instead (as well as in Decryption)? This would save
on random nonce generation and transmission.
Regards,
Martin
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