mirror of https://github.com/cheat/cheat.git
737 lines
19 KiB
Go
737 lines
19 KiB
Go
// Copyright 2011 The Go Authors. 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 packet
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import (
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"bytes"
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"crypto"
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"crypto/cipher"
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"crypto/dsa"
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"crypto/rand"
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"crypto/rsa"
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"crypto/sha1"
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"io"
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"io/ioutil"
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"math/big"
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"strconv"
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"time"
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"github.com/ProtonMail/go-crypto/openpgp/ecdh"
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"github.com/ProtonMail/go-crypto/openpgp/ecdsa"
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"github.com/ProtonMail/go-crypto/openpgp/eddsa"
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"github.com/ProtonMail/go-crypto/openpgp/elgamal"
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"github.com/ProtonMail/go-crypto/openpgp/errors"
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"github.com/ProtonMail/go-crypto/openpgp/internal/encoding"
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"github.com/ProtonMail/go-crypto/openpgp/s2k"
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)
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// PrivateKey represents a possibly encrypted private key. See RFC 4880,
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// section 5.5.3.
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type PrivateKey struct {
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PublicKey
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Encrypted bool // if true then the private key is unavailable until Decrypt has been called.
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encryptedData []byte
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cipher CipherFunction
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s2k func(out, in []byte)
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// An *{rsa|dsa|elgamal|ecdh|ecdsa|ed25519}.PrivateKey or
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// crypto.Signer/crypto.Decrypter (Decryptor RSA only).
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PrivateKey interface{}
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sha1Checksum bool
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iv []byte
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// Type of encryption of the S2K packet
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// Allowed values are 0 (Not encrypted), 254 (SHA1), or
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// 255 (2-byte checksum)
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s2kType S2KType
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// Full parameters of the S2K packet
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s2kParams *s2k.Params
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}
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//S2KType s2k packet type
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type S2KType uint8
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const (
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// S2KNON unencrypt
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S2KNON S2KType = 0
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// S2KSHA1 sha1 sum check
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S2KSHA1 S2KType = 254
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// S2KCHECKSUM sum check
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S2KCHECKSUM S2KType = 255
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)
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func NewRSAPrivateKey(creationTime time.Time, priv *rsa.PrivateKey) *PrivateKey {
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pk := new(PrivateKey)
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pk.PublicKey = *NewRSAPublicKey(creationTime, &priv.PublicKey)
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pk.PrivateKey = priv
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return pk
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}
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func NewDSAPrivateKey(creationTime time.Time, priv *dsa.PrivateKey) *PrivateKey {
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pk := new(PrivateKey)
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pk.PublicKey = *NewDSAPublicKey(creationTime, &priv.PublicKey)
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pk.PrivateKey = priv
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return pk
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}
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func NewElGamalPrivateKey(creationTime time.Time, priv *elgamal.PrivateKey) *PrivateKey {
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pk := new(PrivateKey)
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pk.PublicKey = *NewElGamalPublicKey(creationTime, &priv.PublicKey)
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pk.PrivateKey = priv
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return pk
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}
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func NewECDSAPrivateKey(creationTime time.Time, priv *ecdsa.PrivateKey) *PrivateKey {
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pk := new(PrivateKey)
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pk.PublicKey = *NewECDSAPublicKey(creationTime, &priv.PublicKey)
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pk.PrivateKey = priv
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return pk
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}
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func NewEdDSAPrivateKey(creationTime time.Time, priv *eddsa.PrivateKey) *PrivateKey {
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pk := new(PrivateKey)
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pk.PublicKey = *NewEdDSAPublicKey(creationTime, &priv.PublicKey)
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pk.PrivateKey = priv
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return pk
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}
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func NewECDHPrivateKey(creationTime time.Time, priv *ecdh.PrivateKey) *PrivateKey {
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pk := new(PrivateKey)
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pk.PublicKey = *NewECDHPublicKey(creationTime, &priv.PublicKey)
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pk.PrivateKey = priv
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return pk
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}
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// NewSignerPrivateKey creates a PrivateKey from a crypto.Signer that
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// implements RSA, ECDSA or EdDSA.
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func NewSignerPrivateKey(creationTime time.Time, signer interface{}) *PrivateKey {
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pk := new(PrivateKey)
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// In general, the public Keys should be used as pointers. We still
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// type-switch on the values, for backwards-compatibility.
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switch pubkey := signer.(type) {
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case *rsa.PrivateKey:
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pk.PublicKey = *NewRSAPublicKey(creationTime, &pubkey.PublicKey)
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case rsa.PrivateKey:
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pk.PublicKey = *NewRSAPublicKey(creationTime, &pubkey.PublicKey)
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case *ecdsa.PrivateKey:
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pk.PublicKey = *NewECDSAPublicKey(creationTime, &pubkey.PublicKey)
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case ecdsa.PrivateKey:
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pk.PublicKey = *NewECDSAPublicKey(creationTime, &pubkey.PublicKey)
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case *eddsa.PrivateKey:
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pk.PublicKey = *NewEdDSAPublicKey(creationTime, &pubkey.PublicKey)
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case eddsa.PrivateKey:
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pk.PublicKey = *NewEdDSAPublicKey(creationTime, &pubkey.PublicKey)
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default:
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panic("openpgp: unknown signer type in NewSignerPrivateKey")
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}
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pk.PrivateKey = signer
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return pk
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}
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// NewDecrypterPrivateKey creates a PrivateKey from a *{rsa|elgamal|ecdh}.PrivateKey.
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func NewDecrypterPrivateKey(creationTime time.Time, decrypter interface{}) *PrivateKey {
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pk := new(PrivateKey)
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switch priv := decrypter.(type) {
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case *rsa.PrivateKey:
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pk.PublicKey = *NewRSAPublicKey(creationTime, &priv.PublicKey)
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case *elgamal.PrivateKey:
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pk.PublicKey = *NewElGamalPublicKey(creationTime, &priv.PublicKey)
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case *ecdh.PrivateKey:
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pk.PublicKey = *NewECDHPublicKey(creationTime, &priv.PublicKey)
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default:
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panic("openpgp: unknown decrypter type in NewDecrypterPrivateKey")
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}
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pk.PrivateKey = decrypter
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return pk
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}
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func (pk *PrivateKey) parse(r io.Reader) (err error) {
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err = (&pk.PublicKey).parse(r)
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if err != nil {
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return
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}
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v5 := pk.PublicKey.Version == 5
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var buf [1]byte
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_, err = readFull(r, buf[:])
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if err != nil {
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return
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}
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pk.s2kType = S2KType(buf[0])
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var optCount [1]byte
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if v5 {
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if _, err = readFull(r, optCount[:]); err != nil {
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return
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}
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}
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switch pk.s2kType {
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case S2KNON:
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pk.s2k = nil
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pk.Encrypted = false
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case S2KSHA1, S2KCHECKSUM:
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if v5 && pk.s2kType == S2KCHECKSUM {
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return errors.StructuralError("wrong s2k identifier for version 5")
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}
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_, err = readFull(r, buf[:])
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if err != nil {
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return
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}
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pk.cipher = CipherFunction(buf[0])
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pk.s2kParams, err = s2k.ParseIntoParams(r)
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if err != nil {
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return
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}
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if pk.s2kParams.Dummy() {
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return
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}
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pk.s2k, err = pk.s2kParams.Function()
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if err != nil {
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return
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}
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pk.Encrypted = true
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if pk.s2kType == S2KSHA1 {
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pk.sha1Checksum = true
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}
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default:
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return errors.UnsupportedError("deprecated s2k function in private key")
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}
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if pk.Encrypted {
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blockSize := pk.cipher.blockSize()
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if blockSize == 0 {
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return errors.UnsupportedError("unsupported cipher in private key: " + strconv.Itoa(int(pk.cipher)))
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}
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pk.iv = make([]byte, blockSize)
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_, err = readFull(r, pk.iv)
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if err != nil {
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return
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}
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}
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var privateKeyData []byte
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if v5 {
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var n [4]byte /* secret material four octet count */
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_, err = readFull(r, n[:])
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if err != nil {
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return
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}
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count := uint32(uint32(n[0])<<24 | uint32(n[1])<<16 | uint32(n[2])<<8 | uint32(n[3]))
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if !pk.Encrypted {
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count = count + 2 /* two octet checksum */
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}
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privateKeyData = make([]byte, count)
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_, err = readFull(r, privateKeyData)
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if err != nil {
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return
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}
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} else {
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privateKeyData, err = ioutil.ReadAll(r)
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if err != nil {
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return
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}
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}
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if !pk.Encrypted {
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if len(privateKeyData) < 2 {
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return errors.StructuralError("truncated private key data")
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}
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var sum uint16
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for i := 0; i < len(privateKeyData)-2; i++ {
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sum += uint16(privateKeyData[i])
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}
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if privateKeyData[len(privateKeyData)-2] != uint8(sum>>8) ||
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privateKeyData[len(privateKeyData)-1] != uint8(sum) {
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return errors.StructuralError("private key checksum failure")
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}
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privateKeyData = privateKeyData[:len(privateKeyData)-2]
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return pk.parsePrivateKey(privateKeyData)
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}
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pk.encryptedData = privateKeyData
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return
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}
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// Dummy returns true if the private key is a dummy key. This is a GNU extension.
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func (pk *PrivateKey) Dummy() bool {
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return pk.s2kParams.Dummy()
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}
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func mod64kHash(d []byte) uint16 {
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var h uint16
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for _, b := range d {
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h += uint16(b)
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}
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return h
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}
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func (pk *PrivateKey) Serialize(w io.Writer) (err error) {
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contents := bytes.NewBuffer(nil)
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err = pk.PublicKey.serializeWithoutHeaders(contents)
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if err != nil {
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return
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}
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if _, err = contents.Write([]byte{uint8(pk.s2kType)}); err != nil {
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return
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}
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optional := bytes.NewBuffer(nil)
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if pk.Encrypted || pk.Dummy() {
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optional.Write([]byte{uint8(pk.cipher)})
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if err := pk.s2kParams.Serialize(optional); err != nil {
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return err
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}
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if pk.Encrypted {
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optional.Write(pk.iv)
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}
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}
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if pk.Version == 5 {
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contents.Write([]byte{uint8(optional.Len())})
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}
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io.Copy(contents, optional)
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if !pk.Dummy() {
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l := 0
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var priv []byte
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if !pk.Encrypted {
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buf := bytes.NewBuffer(nil)
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err = pk.serializePrivateKey(buf)
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if err != nil {
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return err
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}
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l = buf.Len()
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checksum := mod64kHash(buf.Bytes())
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buf.Write([]byte{byte(checksum >> 8), byte(checksum)})
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priv = buf.Bytes()
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} else {
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priv, l = pk.encryptedData, len(pk.encryptedData)
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}
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if pk.Version == 5 {
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contents.Write([]byte{byte(l >> 24), byte(l >> 16), byte(l >> 8), byte(l)})
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}
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contents.Write(priv)
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}
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ptype := packetTypePrivateKey
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if pk.IsSubkey {
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ptype = packetTypePrivateSubkey
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}
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err = serializeHeader(w, ptype, contents.Len())
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if err != nil {
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return
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}
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_, err = io.Copy(w, contents)
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if err != nil {
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return
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}
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return
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}
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func serializeRSAPrivateKey(w io.Writer, priv *rsa.PrivateKey) error {
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if _, err := w.Write(new(encoding.MPI).SetBig(priv.D).EncodedBytes()); err != nil {
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return err
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}
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if _, err := w.Write(new(encoding.MPI).SetBig(priv.Primes[1]).EncodedBytes()); err != nil {
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return err
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}
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if _, err := w.Write(new(encoding.MPI).SetBig(priv.Primes[0]).EncodedBytes()); err != nil {
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return err
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}
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_, err := w.Write(new(encoding.MPI).SetBig(priv.Precomputed.Qinv).EncodedBytes())
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return err
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}
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func serializeDSAPrivateKey(w io.Writer, priv *dsa.PrivateKey) error {
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_, err := w.Write(new(encoding.MPI).SetBig(priv.X).EncodedBytes())
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return err
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}
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func serializeElGamalPrivateKey(w io.Writer, priv *elgamal.PrivateKey) error {
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_, err := w.Write(new(encoding.MPI).SetBig(priv.X).EncodedBytes())
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return err
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}
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func serializeECDSAPrivateKey(w io.Writer, priv *ecdsa.PrivateKey) error {
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_, err := w.Write(encoding.NewMPI(priv.MarshalIntegerSecret()).EncodedBytes())
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return err
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}
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func serializeEdDSAPrivateKey(w io.Writer, priv *eddsa.PrivateKey) error {
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_, err := w.Write(encoding.NewMPI(priv.MarshalByteSecret()).EncodedBytes())
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return err
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}
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func serializeECDHPrivateKey(w io.Writer, priv *ecdh.PrivateKey) error {
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_, err := w.Write(encoding.NewMPI(priv.MarshalByteSecret()).EncodedBytes())
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return err
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}
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// Decrypt decrypts an encrypted private key using a passphrase.
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func (pk *PrivateKey) Decrypt(passphrase []byte) error {
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if pk.Dummy() {
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return errors.ErrDummyPrivateKey("dummy key found")
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}
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if !pk.Encrypted {
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return nil
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}
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key := make([]byte, pk.cipher.KeySize())
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pk.s2k(key, passphrase)
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block := pk.cipher.new(key)
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cfb := cipher.NewCFBDecrypter(block, pk.iv)
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data := make([]byte, len(pk.encryptedData))
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cfb.XORKeyStream(data, pk.encryptedData)
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if pk.sha1Checksum {
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if len(data) < sha1.Size {
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return errors.StructuralError("truncated private key data")
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}
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h := sha1.New()
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h.Write(data[:len(data)-sha1.Size])
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sum := h.Sum(nil)
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if !bytes.Equal(sum, data[len(data)-sha1.Size:]) {
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return errors.StructuralError("private key checksum failure")
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}
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data = data[:len(data)-sha1.Size]
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} else {
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if len(data) < 2 {
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return errors.StructuralError("truncated private key data")
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}
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var sum uint16
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for i := 0; i < len(data)-2; i++ {
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sum += uint16(data[i])
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}
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if data[len(data)-2] != uint8(sum>>8) ||
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data[len(data)-1] != uint8(sum) {
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return errors.StructuralError("private key checksum failure")
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}
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data = data[:len(data)-2]
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}
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err := pk.parsePrivateKey(data)
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if _, ok := err.(errors.KeyInvalidError); ok {
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return errors.KeyInvalidError("invalid key parameters")
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}
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if err != nil {
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return err
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}
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// Mark key as unencrypted
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pk.s2kType = S2KNON
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pk.s2k = nil
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pk.Encrypted = false
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pk.encryptedData = nil
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return nil
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}
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// Encrypt encrypts an unencrypted private key using a passphrase.
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func (pk *PrivateKey) Encrypt(passphrase []byte) error {
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priv := bytes.NewBuffer(nil)
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err := pk.serializePrivateKey(priv)
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if err != nil {
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return err
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}
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//Default config of private key encryption
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pk.cipher = CipherAES256
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s2kConfig := &s2k.Config{
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S2KMode: 3, //Iterated
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S2KCount: 65536,
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Hash: crypto.SHA256,
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}
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pk.s2kParams, err = s2k.Generate(rand.Reader, s2kConfig)
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if err != nil {
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return err
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}
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privateKeyBytes := priv.Bytes()
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key := make([]byte, pk.cipher.KeySize())
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pk.sha1Checksum = true
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pk.s2k, err = pk.s2kParams.Function()
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if err != nil {
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return err
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}
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pk.s2k(key, passphrase)
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block := pk.cipher.new(key)
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pk.iv = make([]byte, pk.cipher.blockSize())
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_, err = rand.Read(pk.iv)
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if err != nil {
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return err
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}
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cfb := cipher.NewCFBEncrypter(block, pk.iv)
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if pk.sha1Checksum {
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pk.s2kType = S2KSHA1
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h := sha1.New()
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h.Write(privateKeyBytes)
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sum := h.Sum(nil)
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privateKeyBytes = append(privateKeyBytes, sum...)
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} else {
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pk.s2kType = S2KCHECKSUM
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var sum uint16
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for _, b := range privateKeyBytes {
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sum += uint16(b)
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}
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priv.Write([]byte{uint8(sum >> 8), uint8(sum)})
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}
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pk.encryptedData = make([]byte, len(privateKeyBytes))
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cfb.XORKeyStream(pk.encryptedData, privateKeyBytes)
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pk.Encrypted = true
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pk.PrivateKey = nil
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return err
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}
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func (pk *PrivateKey) serializePrivateKey(w io.Writer) (err error) {
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switch priv := pk.PrivateKey.(type) {
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case *rsa.PrivateKey:
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err = serializeRSAPrivateKey(w, priv)
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case *dsa.PrivateKey:
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err = serializeDSAPrivateKey(w, priv)
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case *elgamal.PrivateKey:
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err = serializeElGamalPrivateKey(w, priv)
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case *ecdsa.PrivateKey:
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err = serializeECDSAPrivateKey(w, priv)
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case *eddsa.PrivateKey:
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err = serializeEdDSAPrivateKey(w, priv)
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case *ecdh.PrivateKey:
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err = serializeECDHPrivateKey(w, priv)
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default:
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err = errors.InvalidArgumentError("unknown private key type")
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}
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return
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}
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|
|
func (pk *PrivateKey) parsePrivateKey(data []byte) (err error) {
|
|
switch pk.PublicKey.PubKeyAlgo {
|
|
case PubKeyAlgoRSA, PubKeyAlgoRSASignOnly, PubKeyAlgoRSAEncryptOnly:
|
|
return pk.parseRSAPrivateKey(data)
|
|
case PubKeyAlgoDSA:
|
|
return pk.parseDSAPrivateKey(data)
|
|
case PubKeyAlgoElGamal:
|
|
return pk.parseElGamalPrivateKey(data)
|
|
case PubKeyAlgoECDSA:
|
|
return pk.parseECDSAPrivateKey(data)
|
|
case PubKeyAlgoECDH:
|
|
return pk.parseECDHPrivateKey(data)
|
|
case PubKeyAlgoEdDSA:
|
|
return pk.parseEdDSAPrivateKey(data)
|
|
}
|
|
panic("impossible")
|
|
}
|
|
|
|
func (pk *PrivateKey) parseRSAPrivateKey(data []byte) (err error) {
|
|
rsaPub := pk.PublicKey.PublicKey.(*rsa.PublicKey)
|
|
rsaPriv := new(rsa.PrivateKey)
|
|
rsaPriv.PublicKey = *rsaPub
|
|
|
|
buf := bytes.NewBuffer(data)
|
|
d := new(encoding.MPI)
|
|
if _, err := d.ReadFrom(buf); err != nil {
|
|
return err
|
|
}
|
|
|
|
p := new(encoding.MPI)
|
|
if _, err := p.ReadFrom(buf); err != nil {
|
|
return err
|
|
}
|
|
|
|
q := new(encoding.MPI)
|
|
if _, err := q.ReadFrom(buf); err != nil {
|
|
return err
|
|
}
|
|
|
|
rsaPriv.D = new(big.Int).SetBytes(d.Bytes())
|
|
rsaPriv.Primes = make([]*big.Int, 2)
|
|
rsaPriv.Primes[0] = new(big.Int).SetBytes(p.Bytes())
|
|
rsaPriv.Primes[1] = new(big.Int).SetBytes(q.Bytes())
|
|
if err := rsaPriv.Validate(); err != nil {
|
|
return errors.KeyInvalidError(err.Error())
|
|
}
|
|
rsaPriv.Precompute()
|
|
pk.PrivateKey = rsaPriv
|
|
|
|
return nil
|
|
}
|
|
|
|
func (pk *PrivateKey) parseDSAPrivateKey(data []byte) (err error) {
|
|
dsaPub := pk.PublicKey.PublicKey.(*dsa.PublicKey)
|
|
dsaPriv := new(dsa.PrivateKey)
|
|
dsaPriv.PublicKey = *dsaPub
|
|
|
|
buf := bytes.NewBuffer(data)
|
|
x := new(encoding.MPI)
|
|
if _, err := x.ReadFrom(buf); err != nil {
|
|
return err
|
|
}
|
|
|
|
dsaPriv.X = new(big.Int).SetBytes(x.Bytes())
|
|
if err := validateDSAParameters(dsaPriv); err != nil {
|
|
return err
|
|
}
|
|
pk.PrivateKey = dsaPriv
|
|
|
|
return nil
|
|
}
|
|
|
|
func (pk *PrivateKey) parseElGamalPrivateKey(data []byte) (err error) {
|
|
pub := pk.PublicKey.PublicKey.(*elgamal.PublicKey)
|
|
priv := new(elgamal.PrivateKey)
|
|
priv.PublicKey = *pub
|
|
|
|
buf := bytes.NewBuffer(data)
|
|
x := new(encoding.MPI)
|
|
if _, err := x.ReadFrom(buf); err != nil {
|
|
return err
|
|
}
|
|
|
|
priv.X = new(big.Int).SetBytes(x.Bytes())
|
|
if err := validateElGamalParameters(priv); err != nil {
|
|
return err
|
|
}
|
|
pk.PrivateKey = priv
|
|
|
|
return nil
|
|
}
|
|
|
|
func (pk *PrivateKey) parseECDSAPrivateKey(data []byte) (err error) {
|
|
ecdsaPub := pk.PublicKey.PublicKey.(*ecdsa.PublicKey)
|
|
ecdsaPriv := ecdsa.NewPrivateKey(*ecdsaPub)
|
|
|
|
buf := bytes.NewBuffer(data)
|
|
d := new(encoding.MPI)
|
|
if _, err := d.ReadFrom(buf); err != nil {
|
|
return err
|
|
}
|
|
|
|
if err := ecdsaPriv.UnmarshalIntegerSecret(d.Bytes()); err != nil {
|
|
return err
|
|
}
|
|
if err := ecdsa.Validate(ecdsaPriv); err != nil {
|
|
return err
|
|
}
|
|
pk.PrivateKey = ecdsaPriv
|
|
|
|
return nil
|
|
}
|
|
|
|
func (pk *PrivateKey) parseECDHPrivateKey(data []byte) (err error) {
|
|
ecdhPub := pk.PublicKey.PublicKey.(*ecdh.PublicKey)
|
|
ecdhPriv := ecdh.NewPrivateKey(*ecdhPub)
|
|
|
|
buf := bytes.NewBuffer(data)
|
|
d := new(encoding.MPI)
|
|
if _, err := d.ReadFrom(buf); err != nil {
|
|
return err
|
|
}
|
|
|
|
if err := ecdhPriv.UnmarshalByteSecret(d.Bytes()); err != nil {
|
|
return err
|
|
}
|
|
|
|
if err := ecdh.Validate(ecdhPriv); err != nil {
|
|
return err
|
|
}
|
|
|
|
pk.PrivateKey = ecdhPriv
|
|
|
|
return nil
|
|
}
|
|
|
|
func (pk *PrivateKey) parseEdDSAPrivateKey(data []byte) (err error) {
|
|
eddsaPub := pk.PublicKey.PublicKey.(*eddsa.PublicKey)
|
|
eddsaPriv := eddsa.NewPrivateKey(*eddsaPub)
|
|
eddsaPriv.PublicKey = *eddsaPub
|
|
|
|
buf := bytes.NewBuffer(data)
|
|
d := new(encoding.MPI)
|
|
if _, err := d.ReadFrom(buf); err != nil {
|
|
return err
|
|
}
|
|
|
|
if err = eddsaPriv.UnmarshalByteSecret(d.Bytes()); err != nil {
|
|
return err
|
|
}
|
|
|
|
if err := eddsa.Validate(eddsaPriv); err != nil {
|
|
return err
|
|
}
|
|
|
|
pk.PrivateKey = eddsaPriv
|
|
|
|
return nil
|
|
}
|
|
|
|
func validateDSAParameters(priv *dsa.PrivateKey) error {
|
|
p := priv.P // group prime
|
|
q := priv.Q // subgroup order
|
|
g := priv.G // g has order q mod p
|
|
x := priv.X // secret
|
|
y := priv.Y // y == g**x mod p
|
|
one := big.NewInt(1)
|
|
// expect g, y >= 2 and g < p
|
|
if g.Cmp(one) <= 0 || y.Cmp(one) <= 0 || g.Cmp(p) > 0 {
|
|
return errors.KeyInvalidError("dsa: invalid group")
|
|
}
|
|
// expect p > q
|
|
if p.Cmp(q) <= 0 {
|
|
return errors.KeyInvalidError("dsa: invalid group prime")
|
|
}
|
|
// q should be large enough and divide p-1
|
|
pSub1 := new(big.Int).Sub(p, one)
|
|
if q.BitLen() < 150 || new(big.Int).Mod(pSub1, q).Cmp(big.NewInt(0)) != 0 {
|
|
return errors.KeyInvalidError("dsa: invalid order")
|
|
}
|
|
// confirm that g has order q mod p
|
|
if !q.ProbablyPrime(32) || new(big.Int).Exp(g, q, p).Cmp(one) != 0 {
|
|
return errors.KeyInvalidError("dsa: invalid order")
|
|
}
|
|
// check y
|
|
if new(big.Int).Exp(g, x, p).Cmp(y) != 0 {
|
|
return errors.KeyInvalidError("dsa: mismatching values")
|
|
}
|
|
|
|
return nil
|
|
}
|
|
|
|
func validateElGamalParameters(priv *elgamal.PrivateKey) error {
|
|
p := priv.P // group prime
|
|
g := priv.G // g has order p-1 mod p
|
|
x := priv.X // secret
|
|
y := priv.Y // y == g**x mod p
|
|
one := big.NewInt(1)
|
|
// Expect g, y >= 2 and g < p
|
|
if g.Cmp(one) <= 0 || y.Cmp(one) <= 0 || g.Cmp(p) > 0 {
|
|
return errors.KeyInvalidError("elgamal: invalid group")
|
|
}
|
|
if p.BitLen() < 1024 {
|
|
return errors.KeyInvalidError("elgamal: group order too small")
|
|
}
|
|
pSub1 := new(big.Int).Sub(p, one)
|
|
if new(big.Int).Exp(g, pSub1, p).Cmp(one) != 0 {
|
|
return errors.KeyInvalidError("elgamal: invalid group")
|
|
}
|
|
// Since p-1 is not prime, g might have a smaller order that divides p-1.
|
|
// We cannot confirm the exact order of g, but we make sure it is not too small.
|
|
gExpI := new(big.Int).Set(g)
|
|
i := 1
|
|
threshold := 2 << 17 // we want order > threshold
|
|
for i < threshold {
|
|
i++ // we check every order to make sure key validation is not easily bypassed by guessing y'
|
|
gExpI.Mod(new(big.Int).Mul(gExpI, g), p)
|
|
if gExpI.Cmp(one) == 0 {
|
|
return errors.KeyInvalidError("elgamal: order too small")
|
|
}
|
|
}
|
|
// Check y
|
|
if new(big.Int).Exp(g, x, p).Cmp(y) != 0 {
|
|
return errors.KeyInvalidError("elgamal: mismatching values")
|
|
}
|
|
|
|
return nil
|
|
}
|