Add WnafBase::multiscalar_mul#85
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Computes a sum-of-products `aA + bB + ...` in variable time with w-NAF
multi-exponentiation using the interleaved window method, also known
as Straus' method.
The key insight is that when computing this sum by means of additions
and doublings, the doublings can be shared by performing the additions
within an inner loop.
The API and implementation are inspired in part by `curve25519-dalek`,
namely the `VartimeMultiscalarMul` trait and corresponding
implementation in `straus.rs`.
This results in ~28% speedup on `p256` for a 3 scalar/point input:
ProjectivePoint operations/point-scalar lincomb (variable-time)
time: [149.13 µs 149.80 µs 150.84 µs]
change: [−27.999% −27.645% −27.267%] (p = 0.00 < 0.05)
This is closer to the `VartimeMultiscalarMul` trait in `curve25519-dalek`.
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This was referenced Jun 2, 2026
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@ebfull anything else needed here? Is it targeting the right branch? |
tarcieri
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Jun 18, 2026
This copies over the multiscalar multiplication implementation I originally implemented in the `wnaf` crate and am attempting to upstream to `group` (zkcrypto/group#85) which was in turn inspired by the Straus implementation from curve25519-dalek. I left it out when vendoring the code originally because we weren't using it at the time (only `multiscalar_mul_array` which I previously renamed to just `multiscalar_mul`), but it's helpful in this use case and gives us a similar 15%-16% speedup. high-level operations/lincomb_vartime (2-term) time: [29.102 µs 29.277 µs 29.465 µs] change: [−16.175% −15.781% −15.426%] (p = 0.00 < 0.05) Performance has improved.
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(NOTE: repeat attempt at #82, cherry-picked from RustCrypto#14)
Computes a sum-of-products
aA + bB + ...in variable time with w-NAF multi-exponentiation using the interleaved window method, also known as Straus' method.The key insight is that when computing this sum by means of additions and doublings, the doublings can be shared by performing the additions within an inner loop.
The API and implementation are inspired in part by
curve25519-dalek, namely theVartimeMultiscalarMultrait and corresponding implementation instraus.rs.This results in ~28% speedup on
p256for a 3 scalar/point input: