Generate a new spec for keccak-packed-multi implementation in zkevm-circuits

[CPerezz]

Since the implementation we were working on originally was superset by this one. We should update the keccak spec according to the actual implementation.

This will also be useful so that we can basically audit the actual impl and see if we are missing any constraints or we're not following 100% the keccak specs.

This is a superset of https://github.com/privacy-scaling-explorations/zkevm-circuits/issues/692

[ChihChengLiang]

~~This task only requires us to specify the "bit" implementation~~

[ed255]

@Brechtpd mentioned that he will be working on this

[aguzmant103]

@Brechtpd just confirming, are you currently working on this or should we keep it in the backlog?

[Brechtpd]

I'm currently working on the MPT spec reviewing but if you're waiting on this I can prioritize it (should also be something I can get done faster I guess).

[aguzmant103]

Thanks no worries! We just wanted to know if it was assigned, but I don't think a change in priority is needed. Thanks a lot!

[CPerezz]

I think the MPT spec is significantly more prio than this. Anyway @ed255 could you confirm??

[ed255]

I think the MPT spec is significantly more prio than this. Anyway @ed255 could you confirm??

Both tasks are important, but I think it's ok to prioritize the MPT spec review for now :)

[ed255]

Here are some design notes (from 5 months ago) from Brecht about the keccak packed multi implementation: https://hackmd.io/NaTuIvmaQCybaOYgd-DG1Q?view#Packed-implementation