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.
- `halo2::plonk::{create_proof, verify_proof}` now take instance columns
as slices of values.
- `halo2::plonk::Permutation` has been replaced by a global permutation,
to which columns can be added with `ConstraintSystem::enable_equality`.
- The introduction of blinding rows means that various tests now require
larger circuit parameters.
The coordinate check for an element decomposed using a running sum
is enforced by mul_fixed::Config::running_sum_coords_gate().
Co-authored-by: Jack Grigg <jack@electriccoin.co>
Selectors previously used in the witness_scalar_* APIs, such as
q_scalar_fixed and q_scalar_fixed_short, are now removed. The
remaining selectors have been renamed for clarity.
The coordinates check for scalars decomposed using a running sum
has been moved into the mul_fixed.rs file, instead of being
duplicated in both mul_fixed::base_field_elem and mul_fixed::short.
The decompose_scalar_fixed() method is now only used in
mul_fixed::full_width, and has been moved there.
These are now provided as inputs to the witness_decompose() and
copy_decompose() methods. This allows us to reuse the same config
for different word/window lengths, avoiding a duplicate constraint
creation.
Co-authored-by: Jack Grigg <jack@electriccoin.co>
In the Orchard protocol, only the NullifierK fixed base in used in
scalar multiplication with a base field element.
The mul_fixed_base_field_elem() API does not have to accept fixed
bases other than NullifierK; conversely, NullifierK does not have
to work with the full-width mul_fixed() API.
This decomposes a field element into K-bit windows using a
running sum. Each step of the running sum is range-constrained.
In strict mode, the final output of the running sum is constrained
to be zero.
This helper asserts K <= 3.
The mul_fixed regions use complete addition on the last window,
and incomplete addition on all other windows. However, the complete
addition does not depend on any offsets in the incomplete addition
region, and can be separated into a disjoint region. Since incomplete
addition uses only four advice columns, while complete addition uses
nine, separating the regions would allow the layouter to optimise
their placement.
Co-authored-by: Jack Grigg <jack@electriccoin.co>
We can use the three-bit existing running sum decomposition to
constrain alpha_0 to be within 130 bits. This removes the need for
a 10-bit lookup decomposition of alpha_0.
Co-authored-by: Daira Hopwood <daira@jacaranda.org>
The differences between the final iteration and prior iterations are:
- The final iteration does not constrain (x_T, y_T) to propagate down.
- The final iteration constrains an assigned y_A output instead of a
derived y_A from the next iteration's variables.
We also swap the init_y constraint to match the book.
Co-authored-by: therealyingtong <yingtong@z.cash>
At certain points in the circuit, we need to constrain cells in
advice columns to equal a fixed constant. Instead of defining a
new fixed column for each constant, we pass around a single
shared by all chips, that is included in the permutation over all
advice columns.
This lets us load all needed constants into a single column and
directly constrain advice cells with an equality constraint.
On the LSB of the scalar, we assign a point (x,y) = (x_p, -y_p)
if LSB = 0, and (0,0) otherwise. This if/else condition must be
enforced.
Co-authored-by: Sean Bowe <ewillbefull@gmail.com>
Using these in `OrchardFixedBases::{generator, u}` instead of the
`impl From<OrchardFixedBasesFull> for OrchardFixedBase` means we avoid
computing the Lagrange coefficients for the generator (which were then
immediately dropped).
This decreases proving time in the Action circuit by 53%.
In Orchard nullifier derivation, we multiply the fixed base
K^Orchard by a value encoded as a base field element. This commit
introduces an API that allows using a base field element as the
"scalar" in fixed-base scalar multiplication.
The API currently assumes that the base field element is output by
another instruction (i.e. there is no instruction to directly
witness it).
The magnitude of the short signed scalar must be 64 bits. We decompose
the magnitude into 22 3-bit windows and check that each window is in
the 3-bit range.
However, since the first 21 windows have already accounted for 63 bits,
the last window is constrained to be a single bit.
Simplify the canonicity check for variable-base scalar multiplication,
by range-checking the low 130 bits rather than the low 127 bits.
Signed-off-by: Daira Hopwood <daira@jacaranda.org>
Co-authored-by: ying tong <yingtong@z.cash>
Fixed-base scalar mul makes use of the add_incomplete and add
instructions internally. The full-width and short signed share
some common logic, which is captured in chip::mul_fixed.rs.
The signed short variant introduces additional logic to handle
the scalar's sign. This is done in the submodule mul_fixed::short.