112 lines
4.1 KiB
Go
112 lines
4.1 KiB
Go
// Copyright (c) 2013-2014 The btcsuite developers
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// Copyright (c) 2015-2023 The Decred developers
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// Use of this source code is governed by an ISC
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// license that can be found in the LICENSE file.
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package secp256k1
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import (
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cryptorand "crypto/rand"
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"io"
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)
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// PrivateKey provides facilities for working with secp256k1 private keys within
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// this package and includes functionality such as serializing and parsing them
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// as well as computing their associated public key.
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type PrivateKey struct {
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Key ModNScalar
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}
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// NewPrivateKey instantiates a new private key from a scalar encoded as a
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// big integer.
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func NewPrivateKey(key *ModNScalar) *PrivateKey {
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return &PrivateKey{Key: *key}
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}
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// PrivKeyFromBytes returns a private based on the provided byte slice which is
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// interpreted as an unsigned 256-bit big-endian integer in the range [0, N-1],
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// where N is the order of the curve.
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//
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// WARNING: This means passing a slice with more than 32 bytes is truncated and
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// that truncated value is reduced modulo N. Further, 0 is not a valid private
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// key. It is up to the caller to provide a value in the appropriate range of
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// [1, N-1]. Failure to do so will either result in an invalid private key or
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// potentially weak private keys that have bias that could be exploited.
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//
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// This function primarily exists to provide a mechanism for converting
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// serialized private keys that are already known to be good.
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//
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// Typically callers should make use of GeneratePrivateKey or
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// GeneratePrivateKeyFromRand when creating private keys since they properly
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// handle generation of appropriate values.
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func PrivKeyFromBytes(privKeyBytes []byte) *PrivateKey {
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var privKey PrivateKey
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privKey.Key.SetByteSlice(privKeyBytes)
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return &privKey
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}
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// generatePrivateKey generates and returns a new private key that is suitable
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// for use with secp256k1 using the provided reader as a source of entropy. The
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// provided reader must be a source of cryptographically secure randomness to
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// avoid weak private keys.
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func generatePrivateKey(rand io.Reader) (*PrivateKey, error) {
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// The group order is close enough to 2^256 that there is only roughly a 1
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// in 2^128 chance of generating an invalid private key, so this loop will
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// virtually never run more than a single iteration in practice.
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var key PrivateKey
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var b32 [32]byte
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for valid := false; !valid; {
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if _, err := io.ReadFull(rand, b32[:]); err != nil {
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return nil, err
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}
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// The private key is only valid when it is in the range [1, N-1], where
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// N is the order of the curve.
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overflow := key.Key.SetBytes(&b32)
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valid = (key.Key.IsZeroBit() | overflow) == 0
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}
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zeroArray32(&b32)
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return &key, nil
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}
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// GeneratePrivateKey generates and returns a new cryptographically secure
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// private key that is suitable for use with secp256k1.
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func GeneratePrivateKey() (*PrivateKey, error) {
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return generatePrivateKey(cryptorand.Reader)
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}
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// GeneratePrivateKeyFromRand generates a private key that is suitable for use
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// with secp256k1 using the provided reader as a source of entropy. The
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// provided reader must be a source of cryptographically secure randomness, such
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// as [crypto/rand.Reader], to avoid weak private keys.
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func GeneratePrivateKeyFromRand(rand io.Reader) (*PrivateKey, error) {
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return generatePrivateKey(rand)
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}
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// PubKey computes and returns the public key corresponding to this private key.
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func (p *PrivateKey) PubKey() *PublicKey {
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var result JacobianPoint
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ScalarBaseMultNonConst(&p.Key, &result)
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result.ToAffine()
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return NewPublicKey(&result.X, &result.Y)
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}
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// Zero manually clears the memory associated with the private key. This can be
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// used to explicitly clear key material from memory for enhanced security
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// against memory scraping.
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func (p *PrivateKey) Zero() {
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p.Key.Zero()
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}
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// PrivKeyBytesLen defines the length in bytes of a serialized private key.
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const PrivKeyBytesLen = 32
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// Serialize returns the private key as a 256-bit big-endian binary-encoded
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// number, padded to a length of 32 bytes.
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func (p PrivateKey) Serialize() []byte {
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var privKeyBytes [PrivKeyBytesLen]byte
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p.Key.PutBytes(&privKeyBytes)
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return privKeyBytes[:]
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}
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