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Copy pathprivate.go
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315 lines (278 loc) · 9.11 KB
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// Copyright (c) 2021 Andreas Auernhammer. All rights reserved.
// Use of this source code is governed by a license that can be
// found in the LICENSE file.
package minisign
import (
"crypto"
"crypto/ed25519"
"crypto/rand"
"crypto/subtle"
"encoding/base64"
"encoding/binary"
"errors"
"io"
"io/ioutil"
"strconv"
"strings"
"time"
"golang.org/x/crypto/blake2b"
"golang.org/x/crypto/scrypt"
)
// PrivateKeyFromFile reads and decrypts the private key
// file with the given password.
func PrivateKeyFromFile(password, path string) (PrivateKey, error) {
bytes, err := ioutil.ReadFile(path)
if err != nil {
return PrivateKey{}, err
}
return DecryptKey(password, bytes)
}
// PrivateKey is a minisign private key.
//
// A private key can sign messages to prove the
// their origin and authenticity.
//
// PrivateKey implements the crypto.Signer interface.
type PrivateKey struct {
_ [0]func() // prevent direct comparison: p1 == p2.
id uint64
bytes [ed25519.PrivateKeySize]byte
}
var _ crypto.Signer = (*PrivateKey)(nil) // compiler check
// ID returns the 64 bit key ID.
func (p PrivateKey) ID() uint64 { return p.id }
// Public returns the corresponding public key.
func (p PrivateKey) Public() crypto.PublicKey {
var bytes [ed25519.PublicKeySize]byte
copy(bytes[:], p.bytes[32:])
return PublicKey{
id: p.ID(),
bytes: bytes,
}
}
// Sign signs the given message.
//
// The minisign signature scheme relies on Ed25519 and supports
// plain as well as pre-hashed messages. Therefore, opts can be
// either crypto.Hash(0) to signal that the message has not been
// hashed or crypto.BLAKE2b_512 to signal that the message is a
// BLAKE2b-512 digest. If opts is crypto.BLAKE2b_512 then message
// must be a 64 bytes long.
//
// Minisign signatures are deterministic such that no randomness
// is necessary.
func (p PrivateKey) Sign(_ io.Reader, message []byte, opts crypto.SignerOpts) (signature []byte, err error) {
var (
trustedComment = "timestamp:" + strconv.FormatInt(time.Now().Unix(), 10)
untrustedComment = "signature from private key: " + strings.ToUpper(strconv.FormatUint(p.ID(), 16))
)
switch h := opts.HashFunc(); h {
case crypto.Hash(0):
const isHashed = false
return sign(p, message, trustedComment, untrustedComment, isHashed), nil
case crypto.BLAKE2b_512:
const isHashed = true
if n := len(message); n != blake2b.Size {
return nil, errors.New("minisign: invalid message length " + strconv.Itoa(n))
}
return sign(p, message, trustedComment, untrustedComment, isHashed), nil
default:
return nil, errors.New("minisign: cannot sign messages hashed with " + strconv.Itoa(int(h)))
}
}
// Equal returns true if and only if p and x have equivalent values.
func (p PrivateKey) Equal(x crypto.PrivateKey) bool {
xx, ok := x.(PrivateKey)
if !ok {
return false
}
return p.id == xx.id && subtle.ConstantTimeCompare(p.bytes[:], xx.bytes[:]) == 1
}
const (
scryptAlgorithm = 0x6353 // hex value for "Sc"
blake2bAlgorithm = 0x3242 // hex value for "B2"
scryptOpsLimit = 0x2000000 // max. Scrypt ops limit based on libsodium
scryptMemLimit = 0x40000000 // max. Scrypt mem limit based on libsodium
privateKeySize = 158 // 2 + 2 + 2 + 32 + 8 + 8 + 104
)
// EncryptKey encrypts the private key with the given password
// using some entropy from the RNG of the OS.
func EncryptKey(password string, privateKey PrivateKey) ([]byte, error) {
var privateKeyBytes [72]byte
binary.LittleEndian.PutUint64(privateKeyBytes[:], privateKey.ID())
copy(privateKeyBytes[8:], privateKey.bytes[:])
var salt [32]byte
if _, err := io.ReadFull(rand.Reader, salt[:]); err != nil {
return nil, err
}
var bytes [privateKeySize]byte
binary.LittleEndian.PutUint16(bytes[0:], EdDSA)
binary.LittleEndian.PutUint16(bytes[2:], scryptAlgorithm)
binary.LittleEndian.PutUint16(bytes[4:], blake2bAlgorithm)
const ( // TODO(aead): Callers may want to customize the cost parameters
defaultOps = 33554432 // libsodium OPS_LIMIT_SENSITIVE
defaultMem = 1073741824 // libsodium MEM_LIMIT_SENSITIVE
)
copy(bytes[6:38], salt[:])
binary.LittleEndian.PutUint64(bytes[38:], defaultOps)
binary.LittleEndian.PutUint64(bytes[46:], defaultMem)
copy(bytes[54:], encryptKey(password, salt[:], defaultOps, defaultMem, privateKeyBytes[:]))
const comment = "untrusted comment: minisign encrypted secret key\n"
encodedBytes := make([]byte, len(comment)+base64.StdEncoding.EncodedLen(len(bytes)))
copy(encodedBytes, []byte(comment))
base64.StdEncoding.Encode(encodedBytes[len(comment):], bytes[:])
return encodedBytes, nil
}
var errDecrypt = errors.New("minisign: decryption failed")
// DecryptKey tries to decrypt the encrypted private key with
// the given password.
func DecryptKey(password string, privateKey []byte) (PrivateKey, error) {
privateKey = trimUntrustedComment(privateKey)
bytes := make([]byte, base64.StdEncoding.DecodedLen(len(privateKey)))
n, err := base64.StdEncoding.Decode(bytes, privateKey)
if err != nil {
return PrivateKey{}, err
}
bytes = bytes[:n]
if len(bytes) != privateKeySize {
return PrivateKey{}, errDecrypt
}
if a := binary.LittleEndian.Uint16(bytes[:2]); a != EdDSA {
return PrivateKey{}, errDecrypt
}
if a := binary.LittleEndian.Uint16(bytes[2:4]); a != scryptAlgorithm {
return PrivateKey{}, errDecrypt
}
if a := binary.LittleEndian.Uint16(bytes[4:6]); a != blake2bAlgorithm {
return PrivateKey{}, errDecrypt
}
var (
scryptOps = binary.LittleEndian.Uint64(bytes[38:46])
scryptMem = binary.LittleEndian.Uint64(bytes[46:54])
)
if scryptOps > scryptOpsLimit {
return PrivateKey{}, errDecrypt
}
if scryptMem > scryptMemLimit {
return PrivateKey{}, errDecrypt
}
var salt [32]byte
copy(salt[:], bytes[6:38])
privateKeyBytes, err := decryptKey(password, salt[:], scryptOps, scryptMem, bytes[54:])
if err != nil {
return PrivateKey{}, err
}
key := PrivateKey{
id: binary.LittleEndian.Uint64(privateKeyBytes[:8]),
}
copy(key.bytes[:], privateKeyBytes[8:])
return key, nil
}
// encryptKey encrypts the plaintext and returns a ciphertext by:
// 1. tag = BLAKE2b-256(EdDSA-const || plaintext)
// 2. keystream = Scrypt(password, salt, convert(ops, mem))
// 3. ciphertext = (plaintext || tag) ⊕ keystream
//
// Therefore, decryptKey converts the ops and mem cost parameters
// to the (N, r, p)-tuple expected by Scrypt.
//
// The plaintext must be a private key ID concatenated with a raw
// Ed25519 private key, and therefore, 72 bytes long.
func encryptKey(password string, salt []byte, ops, mem uint64, plaintext []byte) []byte {
const (
plaintextLen = 72
messageLen = 74
ciphertextLen = 104
)
N, r, p := convertScryptParameters(ops, mem)
keystream, err := scrypt.Key([]byte(password), salt, N, r, p, ciphertextLen)
if err != nil {
panic(err)
}
var message [messageLen]byte
binary.LittleEndian.PutUint16(message[:2], EdDSA)
copy(message[2:], plaintext)
checksum := blake2b.Sum256(message[:])
var ciphertext [ciphertextLen]byte
copy(ciphertext[:plaintextLen], plaintext)
copy(ciphertext[plaintextLen:], checksum[:])
for i, k := range keystream {
ciphertext[i] ^= k
}
return ciphertext[:]
}
// decryptKey decrypts the ciphertext and returns a plaintext by:
// 1. keystream = Scrypt(password, salt, convert(ops, mem))
// 2. plaintext || tag = ciphertext ⊕ keystream
// 3. Check that: tag == BLAKE2b-256(EdDSA-const || plaintext)
//
// Therefore, decryptKey converts the ops and mem cost parameters to
// the (N, r, p)-tuple expected by Scrypt.
//
// It returns an error if the ciphertext is not valid - i.e. if the
// tag does not match the BLAKE2b-256 hash value.
func decryptKey(password string, salt []byte, ops, mem uint64, ciphertext []byte) ([]byte, error) {
const (
plaintextLen = 72
messageLen = 74
ciphertextLen = 104
)
if len(ciphertext) != ciphertextLen {
return nil, errDecrypt
}
N, r, p := convertScryptParameters(ops, mem)
keystream, err := scrypt.Key([]byte(password), salt, N, r, p, ciphertextLen)
if err != nil {
return nil, err
}
var plaintext [ciphertextLen]byte
for i, k := range keystream {
plaintext[i] = ciphertext[i] ^ k
}
var (
privateKeyBytes = plaintext[:plaintextLen]
checksum = plaintext[plaintextLen:]
)
var message [messageLen]byte
binary.LittleEndian.PutUint16(message[:2], EdDSA)
copy(message[2:], privateKeyBytes)
if sum := blake2b.Sum256(message[:]); subtle.ConstantTimeCompare(sum[:], checksum[:]) != 1 {
return nil, errDecrypt
}
return privateKeyBytes, nil
}
// convertScryptParameters converts the operational and memory cost
// to the Scrypt parameters N, r and p.
//
// N is the overall memory / CPU cost and r * p has to be lower then
// 2³⁰. Refer to the scrypt.Key docs for more information.
func convertScryptParameters(ops, mem uint64) (N, r, p int) {
const (
minOps = 1 << 15
maxRP = 0x3fffffff
)
if ops < minOps {
ops = minOps
}
if ops < mem/32 {
r, p = 8, 1
for n := 1; n < 63; n++ {
if N = 1 << n; uint64(N) > (ops / (8 * uint64(r))) {
break
}
}
} else {
r = 8
for n := 1; n < 63; n++ {
if N = 1 << n; uint64(N) > (mem / (256 * uint64(r))) {
break
}
}
if rp := (ops / 4) / uint64(N); rp < maxRP {
p = int(rp) / r
} else {
p = maxRP / r
}
}
return N, r, p
}