2012-06-20 08:44:16

by Ronen Shitrit

Subject: GCM counter inc

Hi

According to the GCM NIST publication, the counter increment should be
module 32 bit.
Looking into the crypto code, I can see that when using gcm(aes) the
gcm will use the ctr over aes,
ctr.c is using the crypto_inc with size of blocksize, which is 16 for AES.
in case crypto_inc will overflow in 32bit it will inc the next 32bit...

Is this a bug or am I missing something?

Regards

2012-06-29 11:01:49

by Ronen Shitrit

Subject: Re: GCM counter inc

Can someone verify if it is a bug?

Thanks

On Wed, Jun 20, 2012 at 11:44 AM, Ronen Shitrit <[email protected]> wrote:
> Hi
>
> According to the GCM NIST publication, the counter increment should be
> module 32 bit.
> Looking into the crypto code, I can see that when using gcm(aes) the
> gcm will use the ctr over aes,
> ctr.c is using the crypto_inc with size of blocksize, which is 16 for AES.
> in case crypto_inc will overflow in 32bit it will inc the next 32bit...
>
> Is this a bug or am I missing something?
>
> Regards