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csp.go
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csp.go
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/*
Copyright IBM Corp. All Rights Reserved.
SPDX-License-Identifier: Apache-2.0
*/
package csp
import (
"crypto"
"crypto/ecdsa"
"crypto/elliptic"
"crypto/rand"
"crypto/x509"
"encoding/asn1"
"encoding/pem"
"io"
"io/ioutil"
"math/big"
"os"
"path/filepath"
"strings"
"github.com/pkg/errors"
)
// LoadPrivateKey loads a private key from a file in keystorePath. It looks
// for a file ending in "_sk" and expects a PEM-encoded PKCS8 EC private key.
func LoadPrivateKey(keystorePath string) (*ecdsa.PrivateKey, error) {
var priv *ecdsa.PrivateKey
walkFunc := func(path string, info os.FileInfo, pathErr error) error {
if !strings.HasSuffix(path, "_sk") {
return nil
}
rawKey, err := ioutil.ReadFile(path)
if err != nil {
return err
}
priv, err = parsePrivateKeyPEM(rawKey)
if err != nil {
return errors.WithMessage(err, path)
}
return nil
}
err := filepath.Walk(keystorePath, walkFunc)
if err != nil {
return nil, err
}
return priv, err
}
func parsePrivateKeyPEM(rawKey []byte) (*ecdsa.PrivateKey, error) {
block, _ := pem.Decode(rawKey)
if block == nil {
return nil, errors.New("bytes are not PEM encoded")
}
key, err := x509.ParsePKCS8PrivateKey(block.Bytes)
if err != nil {
return nil, errors.WithMessage(err, "pem bytes are not PKCS8 encoded ")
}
priv, ok := key.(*ecdsa.PrivateKey)
if !ok {
return nil, errors.New("pem bytes do not contain an EC private key")
}
return priv, nil
}
// GeneratePrivateKey creates an EC private key using a P-256 curve and stores
// it in keystorePath.
func GeneratePrivateKey(keystorePath string) (*ecdsa.PrivateKey, error) {
priv, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
if err != nil {
return nil, errors.WithMessage(err, "failed to generate private key")
}
pkcs8Encoded, err := x509.MarshalPKCS8PrivateKey(priv)
if err != nil {
return nil, errors.WithMessage(err, "failed to marshal private key")
}
pemEncoded := pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: pkcs8Encoded})
keyFile := filepath.Join(keystorePath, "priv_sk")
err = ioutil.WriteFile(keyFile, pemEncoded, 0600)
if err != nil {
return nil, errors.WithMessagef(err, "failed to save private key to file %s", keyFile)
}
return priv, err
}
/**
ECDSA signer implements the crypto.Signer interface for ECDSA keys. The
Sign method ensures signatures are created with Low S values since Fabric
normalizes all signatures to Low S.
See https://github.com/bitcoin/bips/blob/master/bip-0146.mediawiki#low_s
for more detail.
*/
type ECDSASigner struct {
PrivateKey *ecdsa.PrivateKey
}
// Public returns the ecdsa.PublicKey associated with PrivateKey.
func (e *ECDSASigner) Public() crypto.PublicKey {
return &e.PrivateKey.PublicKey
}
// Sign signs the digest and ensures that signatures use the Low S value.
func (e *ECDSASigner) Sign(rand io.Reader, digest []byte, opts crypto.SignerOpts) ([]byte, error) {
r, s, err := ecdsa.Sign(rand, e.PrivateKey, digest)
if err != nil {
return nil, err
}
// ensure Low S signatures
sig := toLowS(
e.PrivateKey.PublicKey,
ECDSASignature{
R: r,
S: s,
},
)
// return marshaled aignature
return asn1.Marshal(sig)
}
/**
When using ECDSA, both (r,s) and (r, -s mod n) are valid signatures. In order
to protect against signature malleability attacks, Fabric normalizes all
signatures to a canonical form where s is at most half the order of the curve.
In order to make signatures compliant with what Fabric expects, toLowS creates
signatures in this canonical form.
*/
func toLowS(key ecdsa.PublicKey, sig ECDSASignature) ECDSASignature {
// calculate half order of the curve
halfOrder := new(big.Int).Div(key.Curve.Params().N, big.NewInt(2))
// check if s is greater than half order of curve
if sig.S.Cmp(halfOrder) == 1 {
// Set s to N - s so that s will be less than or equal to half order
sig.S.Sub(key.Params().N, sig.S)
}
return sig
}
type ECDSASignature struct {
R, S *big.Int
}