Re: [P1619-2] Subtle error/ambiguity in EME-2 drawing
I concur, the summation should start at i=2. -- Shai
Colin Sinclair wrote:
> Folks,
>
> I just noticed a subtle but minor error/ambiguity on the EME-2 drawing
> (Figure 2) in the 1619-2 drafts.
>
> It concerns the summations sum(PPP_j) and sum(CCC_j) which used to be called
> SP and SC respectively in the original EME (EME-32-AES-Nov-04.pdf). When
> Shai updated this to EME-2 by back in 2007, these intermediate variables and
> the precise definition of the summation were dropped and this is when the
> drawing became wrong, or at least ambiguous. Compare the pseudocode in
> Tables 3 & 4 which correctly says:
>
> MP = PPP_1 ^ PPP_2 ^ ... ^ PPP_m ^ T_star
> and CCC_1 = MC ^ CCC_2 ^ ... ^ CCC_m ^ T_star
>
> with the drawing which shows:
>
> MP = PPP_1 ^ sum(PPP_i) ^ T_star
> and CCC_1 = MC ^ sum(CCC_i) ^ T_star
>
> Unless the bounds of the summation on the drawing are explicitly stated as
> i=2..m, then the PPP_1 term will cancel and block 1 will be lost! Similarly
> on the ciphertext side.
>
> Sorry I didn't get this to you in time for last week's meeting, I only
> spotted it on the day of the meeting when scanning the latest draft.
>
> Regards,
> Colin.
>
> Colin Sinclair
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