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