elliptic-curve: add MulByGeneratorVartime trait#2381
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Closes #2375 We now have variable-time precomputed basepoint tables that use wNAF when the `basepoint-table` and `alloc` features are enabled, which can be opportunistically used when these features are enabled to accelerate this operation. We use `Group::mul_by_generator` for the constant-time basepoint tables, however for an extension trait this is captured as `MulByGeneratorVartime::mul_by_generator_vartime`. As discussed in the above issue, and inspired by `curve25519-dalek`'s `EdwardsPoint::vartime_double_scalar_mul_basepoint` function, this adds `MulByGeneratorVartime::mul_by_generator_and_mul_add_point_vartime` as a provided method. This function is the core of many signature algorithms, and when the basepoint tables and alloc are unavailable it can fall back to a linear combination and still provide better performance than the naive constant time version.
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Closes #2375
We now have variable-time precomputed basepoint tables that use wNAF when the
basepoint-tableandallocfeatures are enabled, which can be opportunistically used when these features are enabled to accelerate this operation.We use
Group::mul_by_generatorfor the constant-time basepoint tables, however for an extension trait this is captured asMulByGeneratorVartime::mul_by_generator_vartime.As discussed in the above issue, and inspired by
curve25519-dalek'sEdwardsPoint::vartime_double_scalar_mul_basepointfunction, this addsMulByGeneratorVartime::mul_by_generator_and_mul_add_point_vartimeas a provided method. This function is the core of many signature algorithms, and when the basepoint tables and alloc are unavailable it can fall back to a linear combination and still provide better performance than the naive constant time version.