[Authentication] Fwd: Re: Session negotiation

[Brad Hards]

On Thursday 16 July 2009 18:45:16 Michael Leupold wrote:
> I wasn't talking about reuse, I was more or less considering the secrets to
> be passed through a stream cipher that whose state was established on
> session start. After trying I figured it's not the right approach though as
> while the same secret encrypted over and over produces different encrypted
> results they have to be manually padded/unpadded as apparently crypto
> libraries only support padding on the last block encrypted (at least libqca
> does).
I'm confused as to what you're trying to do.  Maybe you can explain again?
If you pass the same inputs into a cipher, then you'll (obviously) get the 
same output.
In this context, the cipher algorithm and mode (e.g. AES128-CBC) takes a key, 
an IV, and the plain text ("secret") and produces some ciphertext. 
[The padding (or lack thereof) is a function of the block mode and algorithm, 
but we might want to use additional padding to avoid disclosing how long the 
plain text is.]

We need to generate the key from some kind of passphrase (or other source, but 
passphrase is what I expect from this). So we need to define how to produce the 
key, and we need to store the IV with the ciphertext version of the secret. I 
think each secret should be encrypted separately (and so have a different IV).

Brad