26 lines
1.0 KiB
Plaintext
26 lines
1.0 KiB
Plaintext
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import "ecc/edwardsAdd" as add;
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import "ecc/edwardsOnCurve" as onCurve;
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from "ecc/babyjubjubParams" import BabyJubJubParams;
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// Function that implements scalar multiplication for a fixed base point
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// Curve parameters are defined with the last argument
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// The exponent is hard-coded to a 256bit scalar, hence we allow wrapping around the group for certain
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// curve parameters.
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// Note that the exponent array is not check to be boolean in this gadget
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// Reference: https://github.com/zcash-hackworks/sapling-crypto/blob/master/src/jubjub/fs.rs#L555
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def main(bool[256] exponent, field[2] pt, BabyJubJubParams context) -> field[2] {
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field[2] infinity = context.INFINITY;
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field[2] mut doubledP = pt;
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field[2] mut accumulatedP = infinity;
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for u32 i in 0..256 {
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u32 j = 255 - i;
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field[2] candidateP = add(accumulatedP, doubledP, context);
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accumulatedP = exponent[j] ? candidateP : accumulatedP;
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doubledP = add(doubledP, doubledP, context);
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}
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assert(onCurve(accumulatedP, context));
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return accumulatedP;
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}
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