72 lines
2.1 KiB
Go
72 lines
2.1 KiB
Go
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// Copyright 2015 Conformal Systems LLC. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package btcec
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import (
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"bytes"
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"compress/zlib"
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"encoding/base64"
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"encoding/binary"
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"io/ioutil"
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)
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//go:generate go run -tags gensecp256k1 genprecomps.go
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// loadS256BytePoints decompresses and deserializes the pre-computed byte points
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// used to accelerate scalar base multiplication for the secp256k1 curve. This
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// approach is used since it allows the compile to use significantly less ram
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// and be performed much faster than it is with hard-coding the final in-memory
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// data structure. At the same time, it is quite fast to generate the in-memory
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// data structure at init time with this approach versus computing the table.
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func loadS256BytePoints() error {
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// There will be no byte points to load when generating them.
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bp := secp256k1BytePoints
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if len(secp256k1BytePoints) == 0 {
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return nil
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}
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// Decompress the pre-computed table used to accelerate scalar base
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// multiplication.
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decoded := make([]byte, base64.StdEncoding.DecodedLen(len(bp)))
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if _, err := base64.StdEncoding.Decode(decoded, bp); err != nil {
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return err
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}
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r, err := zlib.NewReader(bytes.NewReader(decoded))
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if err != nil {
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return err
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}
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serialized, err := ioutil.ReadAll(r)
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if err != nil {
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return err
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}
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// Deserialize the precomputed byte points and set the curve to them.
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offset := 0
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var bytePoints [32][256][3]fieldVal
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for byteNum := 0; byteNum < 32; byteNum++ {
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// All points in this window.
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for i := 0; i < 256; i++ {
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px, py, pz := new(fieldVal), new(fieldVal), new(fieldVal)
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for i := 0; i < 10; i++ {
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px.n[i] = binary.LittleEndian.Uint32(serialized[offset:])
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offset += 4
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}
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for i := 0; i < 10; i++ {
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py.n[i] = binary.LittleEndian.Uint32(serialized[offset:])
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offset += 4
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}
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for i := 0; i < 10; i++ {
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pz.n[i] = binary.LittleEndian.Uint32(serialized[offset:])
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offset += 4
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}
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bytePoints[byteNum][i][0] = *px
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bytePoints[byteNum][i][1] = *py
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bytePoints[byteNum][i][2] = *pz
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}
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}
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secp256k1.bytePoints = &bytePoints
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return nil
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}
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