This is necessary because the blinding factor r can be zero with greater
than negligible probability in an adversarial case, which with incomplete
addition would cause the circuit to compute a commitment that is not on
the curve.
By rearranging the pieces in the gate, we remove a prev() query and
preserve proximity between pieces involved in the same constraint.
This commit also includes several minor fixes:
- use strict mode for decomposition of j in y-coordinate check;
- Name All Polynomial Constraints;
- remove point_repr() helper function;
- variable renaming and docfixes.
Co-authored-by: Jack Grigg <jack@electriccoin.co>
Instead of separately witnessing k_1 and equating it to z1_j, we
can directly make use of z1_j in the gate. This allows us to fit
the region into a 5 x 2 area, improving the layout.
Co-authored-by: Jack Grigg <jack@electriccoin.co>
Even though we only use the LSB of the y-coordinates as inputs to
the Sinsemilla hash, we still have to check that they are consistent
with the g_d and pk_d points that were passed in.
Co-authored-by: Daira Hopwood <daira@jacaranda.org>
Co-authored-by: Jack Grigg <jack@electriccoin.co>
Previously, these two helpers were returning different outputs.
They have now been standardised to return only the full running
sum.
Note the z_0 is the original element being decomposed by the
helper.
Previously, fixed_y_q was a non-binary selector that both loaded
the y_Q value and toggled the y_Q gate.
Now, the gate is toggled by a q_s4 simple selector, while the value
is loaded into a separate fixed column.
The Sinsemilla chip witnesses message pieces in individual regions, and
then copies them into the `hash_piece` region to initialize the running
sum. Previously these occured in the same column, but we can reduce the
utilized rows of the Action circuit by moving these into a less-used
column.
If https://github.com/zcash/halo2/issues/334 is implemented, this change
would be unnecessary, as the witnessed message piece regions would never
be assigned into the circuit.
We were configuring multiple instances of this across all of the advice
columns, in order to spread their assignments. However, we are actually
more constrained by columns than rows, and we have comparatively few
rows of range check logic required for the Action circuit.
We now use a single LookupRangeCheckConfig for the entire circuit. The
reduction in lookup arguments and fixed columns cuts the proof size in
half (now at 6048 bytes when using `floor_planner::V1`).
Co-authored-by: therealyingtong <yingtong@z.cash>
- Move Poseidon into the right-hand advice columns. The Action circuit
has 33 Sinsemilla invocations with 510-bit inputs (the 32 Merkle path
hashes, and Commit^ivk). Poseidon fits within the row count of one of
these invocations, so we can run it in parallel with these.
- Share fixed columns between ECC and Poseidon chips. Poseidon requires
four advice columns, while ECC incomplete addition requires six, so we
could choose to configure them in parallel. However, we only use a
single Poseidon invocation, and we have the rows to accomodate it
serially with fixed-base scalar mul. Sharing the ECC chip's 8 Lagrange
coefficient fixed columns instead reduces the proof size.
- We position Poseidon in the right-most 6 fixed columns, anticipating
a further optimisation to Sinsemilla that will occupy the left-most
2 fixed columns.
Daira Hopwood
Jack Grigg
therealyingtong