bls12: implements Marshaler interfaces and SetBytes for Scalar #277
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| if isLessThan(in, order) == 0 { | ||
| return nil, errInputRange | ||
| } | ||
| return conv.BytesBe2Uint64Le(in), nil | ||
| } | ||
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| func setBytesUnbounded(in []byte, order []byte) []uint64 { | ||
| inBig := new(big.Int).SetBytes(in) | ||
| inBig.Mod(inBig, new(big.Int).SetBytes(order)) |
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this function must be marked as non-constant time. Do you have any ideas on how to perform this operation in constant time?
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What length are we applying it to? I think I only need it for double length ones, in which case a reduction is all that is required.
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One alternative possibility is to take in a reader and use it to extract the requisit number of bytes to use as input to a reduction. Either Montgomery or Barrett would work, but I think with this approach Barrett makes the interface cleaner given the next toMont call. That said we could just go to Montgomery directly here, and avoid needing two reductions.
| if isLessThan(in, order) == 0 { | ||
| return nil, errInputRange | ||
| } | ||
| return conv.BytesBe2Uint64Le(in), nil | ||
| } | ||
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| func setBytesUnbounded(in []byte, order []byte) []uint64 { | ||
| inBig := new(big.Int).SetBytes(in) | ||
| inBig.Mod(inBig, new(big.Int).SetBytes(order)) |
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One alternative possibility is to take in a reader and use it to extract the requisit number of bytes to use as input to a reduction. Either Montgomery or Barrett would work, but I think with this approach Barrett makes the interface cleaner given the next toMont call. That said we could just go to Montgomery directly here, and avoid needing two reductions.
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Implements the Marshaler interfaces from go stdlib for serialization and deserialization.
Also, Scalar exposes
SetBytes([]byte)to set scalars using variable-length data.