57 lines
1.4 KiB
Go
57 lines
1.4 KiB
Go
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// Copyright 2015 Jeffrey Wilcke, Felix Lange, Gustav Simonsson. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be found in
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// the LICENSE file.
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// +build !gofuzz cgo
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package secp256k1
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import (
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"math/big"
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"unsafe"
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)
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/*
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#include "libsecp256k1/include/secp256k1.h"
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extern int secp256k1_ext_scalar_mul(const secp256k1_context* ctx, const unsigned char *point, const unsigned char *scalar);
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*/
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import "C"
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func (BitCurve *BitCurve) ScalarMult(Bx, By *big.Int, scalar []byte) (*big.Int, *big.Int) {
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// Ensure scalar is exactly 32 bytes. We pad always, even if
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// scalar is 32 bytes long, to avoid a timing side channel.
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if len(scalar) > 32 {
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panic("can't handle scalars > 256 bits")
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}
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// NOTE: potential timing issue
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padded := make([]byte, 32)
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copy(padded[32-len(scalar):], scalar)
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scalar = padded
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// Do the multiplication in C, updating point.
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point := make([]byte, 64)
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readBits(Bx, point[:32])
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readBits(By, point[32:])
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pointPtr := (*C.uchar)(unsafe.Pointer(&point[0]))
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scalarPtr := (*C.uchar)(unsafe.Pointer(&scalar[0]))
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res := C.secp256k1_ext_scalar_mul(context, pointPtr, scalarPtr)
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// Unpack the result and clear temporaries.
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x := new(big.Int).SetBytes(point[:32])
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y := new(big.Int).SetBytes(point[32:])
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for i := range point {
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point[i] = 0
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}
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for i := range padded {
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scalar[i] = 0
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}
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if res != 1 {
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return nil, nil
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}
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return x, y
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}
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