chore: vendor

vendor/github.com/ProtonMail/go-crypto/openpgp/packet/public_key.go

@@ -0,0 +1,806 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package packet
+
+import (
+	"crypto"
+	"crypto/dsa"
+	"crypto/rsa"
+	"crypto/sha1"
+	"crypto/sha256"
+	_ "crypto/sha512"
+	"encoding/binary"
+	"fmt"
+	"hash"
+	"io"
+	"math/big"
+	"strconv"
+	"time"
+
+	"github.com/ProtonMail/go-crypto/openpgp/ecdh"
+	"github.com/ProtonMail/go-crypto/openpgp/ecdsa"
+	"github.com/ProtonMail/go-crypto/openpgp/eddsa"
+	"github.com/ProtonMail/go-crypto/openpgp/elgamal"
+	"github.com/ProtonMail/go-crypto/openpgp/errors"
+	"github.com/ProtonMail/go-crypto/openpgp/internal/algorithm"
+	"github.com/ProtonMail/go-crypto/openpgp/internal/ecc"
+	"github.com/ProtonMail/go-crypto/openpgp/internal/encoding"
+)
+
+type kdfHashFunction byte
+type kdfAlgorithm byte
+
+// PublicKey represents an OpenPGP public key. See RFC 4880, section 5.5.2.
+type PublicKey struct {
+	Version      int
+	CreationTime time.Time
+	PubKeyAlgo   PublicKeyAlgorithm
+	PublicKey    interface{} // *rsa.PublicKey, *dsa.PublicKey, *ecdsa.PublicKey or *eddsa.PublicKey
+	Fingerprint  []byte
+	KeyId        uint64
+	IsSubkey     bool
+
+	// RFC 4880 fields
+	n, e, p, q, g, y encoding.Field
+
+	// RFC 6637 fields
+	// oid contains the OID byte sequence identifying the elliptic curve used
+	oid encoding.Field
+
+	// kdf stores key derivation function parameters
+	// used for ECDH encryption. See RFC 6637, Section 9.
+	kdf encoding.Field
+}
+
+// UpgradeToV5 updates the version of the key to v5, and updates all necessary
+// fields.
+func (pk *PublicKey) UpgradeToV5() {
+	pk.Version = 5
+	pk.setFingerprintAndKeyId()
+}
+
+// signingKey provides a convenient abstraction over signature verification
+// for v3 and v4 public keys.
+type signingKey interface {
+	SerializeForHash(io.Writer) error
+	SerializeSignaturePrefix(io.Writer)
+	serializeWithoutHeaders(io.Writer) error
+}
+
+// NewRSAPublicKey returns a PublicKey that wraps the given rsa.PublicKey.
+func NewRSAPublicKey(creationTime time.Time, pub *rsa.PublicKey) *PublicKey {
+	pk := &PublicKey{
+		Version:      4,
+		CreationTime: creationTime,
+		PubKeyAlgo:   PubKeyAlgoRSA,
+		PublicKey:    pub,
+		n:            new(encoding.MPI).SetBig(pub.N),
+		e:            new(encoding.MPI).SetBig(big.NewInt(int64(pub.E))),
+	}
+
+	pk.setFingerprintAndKeyId()
+	return pk
+}
+
+// NewDSAPublicKey returns a PublicKey that wraps the given dsa.PublicKey.
+func NewDSAPublicKey(creationTime time.Time, pub *dsa.PublicKey) *PublicKey {
+	pk := &PublicKey{
+		Version:      4,
+		CreationTime: creationTime,
+		PubKeyAlgo:   PubKeyAlgoDSA,
+		PublicKey:    pub,
+		p:            new(encoding.MPI).SetBig(pub.P),
+		q:            new(encoding.MPI).SetBig(pub.Q),
+		g:            new(encoding.MPI).SetBig(pub.G),
+		y:            new(encoding.MPI).SetBig(pub.Y),
+	}
+
+	pk.setFingerprintAndKeyId()
+	return pk
+}
+
+// NewElGamalPublicKey returns a PublicKey that wraps the given elgamal.PublicKey.
+func NewElGamalPublicKey(creationTime time.Time, pub *elgamal.PublicKey) *PublicKey {
+	pk := &PublicKey{
+		Version:      4,
+		CreationTime: creationTime,
+		PubKeyAlgo:   PubKeyAlgoElGamal,
+		PublicKey:    pub,
+		p:            new(encoding.MPI).SetBig(pub.P),
+		g:            new(encoding.MPI).SetBig(pub.G),
+		y:            new(encoding.MPI).SetBig(pub.Y),
+	}
+
+	pk.setFingerprintAndKeyId()
+	return pk
+}
+
+func NewECDSAPublicKey(creationTime time.Time, pub *ecdsa.PublicKey) *PublicKey {
+	pk := &PublicKey{
+		Version:      4,
+		CreationTime: creationTime,
+		PubKeyAlgo:   PubKeyAlgoECDSA,
+		PublicKey:    pub,
+		p:            encoding.NewMPI(pub.MarshalPoint()),
+	}
+
+	curveInfo := ecc.FindByCurve(pub.GetCurve())
+	if curveInfo == nil {
+		panic("unknown elliptic curve")
+	}
+	pk.oid = curveInfo.Oid
+	pk.setFingerprintAndKeyId()
+	return pk
+}
+
+func NewECDHPublicKey(creationTime time.Time, pub *ecdh.PublicKey) *PublicKey {
+	var pk *PublicKey
+	var kdf = encoding.NewOID([]byte{0x1, pub.Hash.Id(), pub.Cipher.Id()})
+	pk = &PublicKey{
+		Version:      4,
+		CreationTime: creationTime,
+		PubKeyAlgo:   PubKeyAlgoECDH,
+		PublicKey:    pub,
+		p:            encoding.NewMPI(pub.MarshalPoint()),
+		kdf:          kdf,
+	}
+
+	curveInfo := ecc.FindByCurve(pub.GetCurve())
+
+	if curveInfo == nil {
+		panic("unknown elliptic curve")
+	}
+
+	pk.oid = curveInfo.Oid
+	pk.setFingerprintAndKeyId()
+	return pk
+}
+
+func NewEdDSAPublicKey(creationTime time.Time, pub *eddsa.PublicKey) *PublicKey {
+	curveInfo := ecc.FindByCurve(pub.GetCurve())
+	pk := &PublicKey{
+		Version:      4,
+		CreationTime: creationTime,
+		PubKeyAlgo:   PubKeyAlgoEdDSA,
+		PublicKey:    pub,
+		oid:          curveInfo.Oid,
+		// Native point format, see draft-koch-eddsa-for-openpgp-04, Appendix B
+		p: encoding.NewMPI(pub.MarshalPoint()),
+	}
+
+	pk.setFingerprintAndKeyId()
+	return pk
+}
+
+func (pk *PublicKey) parse(r io.Reader) (err error) {
+	// RFC 4880, section 5.5.2
+	var buf [6]byte
+	_, err = readFull(r, buf[:])
+	if err != nil {
+		return
+	}
+	if buf[0] != 4 && buf[0] != 5 {
+		return errors.UnsupportedError("public key version " + strconv.Itoa(int(buf[0])))
+	}
+
+	pk.Version = int(buf[0])
+	if pk.Version == 5 {
+		var n [4]byte
+		_, err = readFull(r, n[:])
+		if err != nil {
+			return
+		}
+	}
+	pk.CreationTime = time.Unix(int64(uint32(buf[1])<<24|uint32(buf[2])<<16|uint32(buf[3])<<8|uint32(buf[4])), 0)
+	pk.PubKeyAlgo = PublicKeyAlgorithm(buf[5])
+	switch pk.PubKeyAlgo {
+	case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly, PubKeyAlgoRSASignOnly:
+		err = pk.parseRSA(r)
+	case PubKeyAlgoDSA:
+		err = pk.parseDSA(r)
+	case PubKeyAlgoElGamal:
+		err = pk.parseElGamal(r)
+	case PubKeyAlgoECDSA:
+		err = pk.parseECDSA(r)
+	case PubKeyAlgoECDH:
+		err = pk.parseECDH(r)
+	case PubKeyAlgoEdDSA:
+		err = pk.parseEdDSA(r)
+	default:
+		err = errors.UnsupportedError("public key type: " + strconv.Itoa(int(pk.PubKeyAlgo)))
+	}
+	if err != nil {
+		return
+	}
+
+	pk.setFingerprintAndKeyId()
+	return
+}
+
+func (pk *PublicKey) setFingerprintAndKeyId() {
+	// RFC 4880, section 12.2
+	if pk.Version == 5 {
+		fingerprint := sha256.New()
+		pk.SerializeForHash(fingerprint)
+		pk.Fingerprint = make([]byte, 32)
+		copy(pk.Fingerprint, fingerprint.Sum(nil))
+		pk.KeyId = binary.BigEndian.Uint64(pk.Fingerprint[:8])
+	} else {
+		fingerprint := sha1.New()
+		pk.SerializeForHash(fingerprint)
+		pk.Fingerprint = make([]byte, 20)
+		copy(pk.Fingerprint, fingerprint.Sum(nil))
+		pk.KeyId = binary.BigEndian.Uint64(pk.Fingerprint[12:20])
+	}
+}
+
+// parseRSA parses RSA public key material from the given Reader. See RFC 4880,
+// section 5.5.2.
+func (pk *PublicKey) parseRSA(r io.Reader) (err error) {
+	pk.n = new(encoding.MPI)
+	if _, err = pk.n.ReadFrom(r); err != nil {
+		return
+	}
+	pk.e = new(encoding.MPI)
+	if _, err = pk.e.ReadFrom(r); err != nil {
+		return
+	}
+
+	if len(pk.e.Bytes()) > 3 {
+		err = errors.UnsupportedError("large public exponent")
+		return
+	}
+	rsa := &rsa.PublicKey{
+		N: new(big.Int).SetBytes(pk.n.Bytes()),
+		E: 0,
+	}
+	for i := 0; i < len(pk.e.Bytes()); i++ {
+		rsa.E <<= 8
+		rsa.E |= int(pk.e.Bytes()[i])
+	}
+	pk.PublicKey = rsa
+	return
+}
+
+// parseDSA parses DSA public key material from the given Reader. See RFC 4880,
+// section 5.5.2.
+func (pk *PublicKey) parseDSA(r io.Reader) (err error) {
+	pk.p = new(encoding.MPI)
+	if _, err = pk.p.ReadFrom(r); err != nil {
+		return
+	}
+	pk.q = new(encoding.MPI)
+	if _, err = pk.q.ReadFrom(r); err != nil {
+		return
+	}
+	pk.g = new(encoding.MPI)
+	if _, err = pk.g.ReadFrom(r); err != nil {
+		return
+	}
+	pk.y = new(encoding.MPI)
+	if _, err = pk.y.ReadFrom(r); err != nil {
+		return
+	}
+
+	dsa := new(dsa.PublicKey)
+	dsa.P = new(big.Int).SetBytes(pk.p.Bytes())
+	dsa.Q = new(big.Int).SetBytes(pk.q.Bytes())
+	dsa.G = new(big.Int).SetBytes(pk.g.Bytes())
+	dsa.Y = new(big.Int).SetBytes(pk.y.Bytes())
+	pk.PublicKey = dsa
+	return
+}
+
+// parseElGamal parses ElGamal public key material from the given Reader. See
+// RFC 4880, section 5.5.2.
+func (pk *PublicKey) parseElGamal(r io.Reader) (err error) {
+	pk.p = new(encoding.MPI)
+	if _, err = pk.p.ReadFrom(r); err != nil {
+		return
+	}
+	pk.g = new(encoding.MPI)
+	if _, err = pk.g.ReadFrom(r); err != nil {
+		return
+	}
+	pk.y = new(encoding.MPI)
+	if _, err = pk.y.ReadFrom(r); err != nil {
+		return
+	}
+
+	elgamal := new(elgamal.PublicKey)
+	elgamal.P = new(big.Int).SetBytes(pk.p.Bytes())
+	elgamal.G = new(big.Int).SetBytes(pk.g.Bytes())
+	elgamal.Y = new(big.Int).SetBytes(pk.y.Bytes())
+	pk.PublicKey = elgamal
+	return
+}
+
+// parseECDSA parses ECDSA public key material from the given Reader. See
+// RFC 6637, Section 9.
+func (pk *PublicKey) parseECDSA(r io.Reader) (err error) {
+	pk.oid = new(encoding.OID)
+	if _, err = pk.oid.ReadFrom(r); err != nil {
+		return
+	}
+	pk.p = new(encoding.MPI)
+	if _, err = pk.p.ReadFrom(r); err != nil {
+		return
+	}
+
+	curveInfo := ecc.FindByOid(pk.oid)
+	if curveInfo == nil {
+		return errors.UnsupportedError(fmt.Sprintf("unknown oid: %x", pk.oid))
+	}
+
+	c, ok := curveInfo.Curve.(ecc.ECDSACurve)
+	if !ok {
+		return errors.UnsupportedError(fmt.Sprintf("unsupported oid: %x", pk.oid))
+	}
+
+	ecdsaKey := ecdsa.NewPublicKey(c)
+	err = ecdsaKey.UnmarshalPoint(pk.p.Bytes())
+	pk.PublicKey = ecdsaKey
+
+	return
+}
+
+// parseECDH parses ECDH public key material from the given Reader. See
+// RFC 6637, Section 9.
+func (pk *PublicKey) parseECDH(r io.Reader) (err error) {
+	pk.oid = new(encoding.OID)
+	if _, err = pk.oid.ReadFrom(r); err != nil {
+		return
+	}
+	pk.p = new(encoding.MPI)
+	if _, err = pk.p.ReadFrom(r); err != nil {
+		return
+	}
+	pk.kdf = new(encoding.OID)
+	if _, err = pk.kdf.ReadFrom(r); err != nil {
+		return
+	}
+
+	curveInfo := ecc.FindByOid(pk.oid)
+
+	if curveInfo == nil {
+		return errors.UnsupportedError(fmt.Sprintf("unknown oid: %x", pk.oid))
+	}
+
+	c, ok := curveInfo.Curve.(ecc.ECDHCurve)
+	if !ok {
+		return errors.UnsupportedError(fmt.Sprintf("unsupported oid: %x", pk.oid))
+	}
+
+	if kdfLen := len(pk.kdf.Bytes()); kdfLen < 3 {
+		return errors.UnsupportedError("unsupported ECDH KDF length: " + strconv.Itoa(kdfLen))
+	}
+	if reserved := pk.kdf.Bytes()[0]; reserved != 0x01 {
+		return errors.UnsupportedError("unsupported KDF reserved field: " + strconv.Itoa(int(reserved)))
+	}
+	kdfHash, ok := algorithm.HashById[pk.kdf.Bytes()[1]]
+	if !ok {
+		return errors.UnsupportedError("unsupported ECDH KDF hash: " + strconv.Itoa(int(pk.kdf.Bytes()[1])))
+	}
+	kdfCipher, ok := algorithm.CipherById[pk.kdf.Bytes()[2]]
+	if !ok {
+		return errors.UnsupportedError("unsupported ECDH KDF cipher: " + strconv.Itoa(int(pk.kdf.Bytes()[2])))
+	}
+
+	ecdhKey := ecdh.NewPublicKey(c, kdfHash, kdfCipher)
+	err = ecdhKey.UnmarshalPoint(pk.p.Bytes())
+	pk.PublicKey = ecdhKey
+
+	return
+}
+
+func (pk *PublicKey) parseEdDSA(r io.Reader) (err error) {
+	pk.oid = new(encoding.OID)
+	if _, err = pk.oid.ReadFrom(r); err != nil {
+		return
+	}
+	curveInfo := ecc.FindByOid(pk.oid)
+	if curveInfo == nil {
+		return errors.UnsupportedError(fmt.Sprintf("unknown oid: %x", pk.oid))
+	}
+
+	c, ok := curveInfo.Curve.(ecc.EdDSACurve)
+	if !ok {
+		return errors.UnsupportedError(fmt.Sprintf("unsupported oid: %x", pk.oid))
+	}
+
+	pk.p = new(encoding.MPI)
+	if _, err = pk.p.ReadFrom(r); err != nil {
+		return
+	}
+
+	if len(pk.p.Bytes()) == 0 {
+		return errors.StructuralError("empty EdDSA public key")
+	}
+
+	pub := eddsa.NewPublicKey(c)
+
+	switch flag := pk.p.Bytes()[0]; flag {
+	case 0x04:
+		// TODO: see _grcy_ecc_eddsa_ensure_compact in grcypt
+		return errors.UnsupportedError("unsupported EdDSA compression: " + strconv.Itoa(int(flag)))
+	case 0x40:
+		err = pub.UnmarshalPoint(pk.p.Bytes())
+	default:
+		return errors.UnsupportedError("unsupported EdDSA compression: " + strconv.Itoa(int(flag)))
+	}
+
+	pk.PublicKey = pub
+	return
+}
+
+// SerializeForHash serializes the PublicKey to w with the special packet
+// header format needed for hashing.
+func (pk *PublicKey) SerializeForHash(w io.Writer) error {
+	pk.SerializeSignaturePrefix(w)
+	return pk.serializeWithoutHeaders(w)
+}
+
+// SerializeSignaturePrefix writes the prefix for this public key to the given Writer.
+// The prefix is used when calculating a signature over this public key. See
+// RFC 4880, section 5.2.4.
+func (pk *PublicKey) SerializeSignaturePrefix(w io.Writer) {
+	var pLength = pk.algorithmSpecificByteCount()
+	if pk.Version == 5 {
+		pLength += 10 // version, timestamp (4), algorithm, key octet count (4).
+		w.Write([]byte{
+			0x9A,
+			byte(pLength >> 24),
+			byte(pLength >> 16),
+			byte(pLength >> 8),
+			byte(pLength),
+		})
+		return
+	}
+	pLength += 6
+	w.Write([]byte{0x99, byte(pLength >> 8), byte(pLength)})
+}
+
+func (pk *PublicKey) Serialize(w io.Writer) (err error) {
+	length := 6 // 6 byte header
+	length += pk.algorithmSpecificByteCount()
+	if pk.Version == 5 {
+		length += 4 // octet key count
+	}
+	packetType := packetTypePublicKey
+	if pk.IsSubkey {
+		packetType = packetTypePublicSubkey
+	}
+	err = serializeHeader(w, packetType, length)
+	if err != nil {
+		return
+	}
+	return pk.serializeWithoutHeaders(w)
+}
+
+func (pk *PublicKey) algorithmSpecificByteCount() int {
+	length := 0
+	switch pk.PubKeyAlgo {
+	case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly, PubKeyAlgoRSASignOnly:
+		length += int(pk.n.EncodedLength())
+		length += int(pk.e.EncodedLength())
+	case PubKeyAlgoDSA:
+		length += int(pk.p.EncodedLength())
+		length += int(pk.q.EncodedLength())
+		length += int(pk.g.EncodedLength())
+		length += int(pk.y.EncodedLength())
+	case PubKeyAlgoElGamal:
+		length += int(pk.p.EncodedLength())
+		length += int(pk.g.EncodedLength())
+		length += int(pk.y.EncodedLength())
+	case PubKeyAlgoECDSA:
+		length += int(pk.oid.EncodedLength())
+		length += int(pk.p.EncodedLength())
+	case PubKeyAlgoECDH:
+		length += int(pk.oid.EncodedLength())
+		length += int(pk.p.EncodedLength())
+		length += int(pk.kdf.EncodedLength())
+	case PubKeyAlgoEdDSA:
+		length += int(pk.oid.EncodedLength())
+		length += int(pk.p.EncodedLength())
+	default:
+		panic("unknown public key algorithm")
+	}
+	return length
+}
+
+// serializeWithoutHeaders marshals the PublicKey to w in the form of an
+// OpenPGP public key packet, not including the packet header.
+func (pk *PublicKey) serializeWithoutHeaders(w io.Writer) (err error) {
+	t := uint32(pk.CreationTime.Unix())
+	if _, err = w.Write([]byte{
+		byte(pk.Version),
+		byte(t >> 24), byte(t >> 16), byte(t >> 8), byte(t),
+		byte(pk.PubKeyAlgo),
+	}); err != nil {
+		return
+	}
+
+	if pk.Version == 5 {
+		n := pk.algorithmSpecificByteCount()
+		if _, err = w.Write([]byte{
+			byte(n >> 24), byte(n >> 16), byte(n >> 8), byte(n),
+		}); err != nil {
+			return
+		}
+	}
+
+	switch pk.PubKeyAlgo {
+	case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly, PubKeyAlgoRSASignOnly:
+		if _, err = w.Write(pk.n.EncodedBytes()); err != nil {
+			return
+		}
+		_, err = w.Write(pk.e.EncodedBytes())
+		return
+	case PubKeyAlgoDSA:
+		if _, err = w.Write(pk.p.EncodedBytes()); err != nil {
+			return
+		}
+		if _, err = w.Write(pk.q.EncodedBytes()); err != nil {
+			return
+		}
+		if _, err = w.Write(pk.g.EncodedBytes()); err != nil {
+			return
+		}
+		_, err = w.Write(pk.y.EncodedBytes())
+		return
+	case PubKeyAlgoElGamal:
+		if _, err = w.Write(pk.p.EncodedBytes()); err != nil {
+			return
+		}
+		if _, err = w.Write(pk.g.EncodedBytes()); err != nil {
+			return
+		}
+		_, err = w.Write(pk.y.EncodedBytes())
+		return
+	case PubKeyAlgoECDSA:
+		if _, err = w.Write(pk.oid.EncodedBytes()); err != nil {
+			return
+		}
+		_, err = w.Write(pk.p.EncodedBytes())
+		return
+	case PubKeyAlgoECDH:
+		if _, err = w.Write(pk.oid.EncodedBytes()); err != nil {
+			return
+		}
+		if _, err = w.Write(pk.p.EncodedBytes()); err != nil {
+			return
+		}
+		_, err = w.Write(pk.kdf.EncodedBytes())
+		return
+	case PubKeyAlgoEdDSA:
+		if _, err = w.Write(pk.oid.EncodedBytes()); err != nil {
+			return
+		}
+		_, err = w.Write(pk.p.EncodedBytes())
+		return
+	}
+	return errors.InvalidArgumentError("bad public-key algorithm")
+}
+
+// CanSign returns true iff this public key can generate signatures
+func (pk *PublicKey) CanSign() bool {
+	return pk.PubKeyAlgo != PubKeyAlgoRSAEncryptOnly && pk.PubKeyAlgo != PubKeyAlgoElGamal && pk.PubKeyAlgo != PubKeyAlgoECDH
+}
+
+// VerifySignature returns nil iff sig is a valid signature, made by this
+// public key, of the data hashed into signed. signed is mutated by this call.
+func (pk *PublicKey) VerifySignature(signed hash.Hash, sig *Signature) (err error) {
+	if !pk.CanSign() {
+		return errors.InvalidArgumentError("public key cannot generate signatures")
+	}
+	if sig.Version == 5 && (sig.SigType == 0x00 || sig.SigType == 0x01) {
+		sig.AddMetadataToHashSuffix()
+	}
+	signed.Write(sig.HashSuffix)
+	hashBytes := signed.Sum(nil)
+	if sig.Version == 5 && (hashBytes[0] != sig.HashTag[0] || hashBytes[1] != sig.HashTag[1]) {
+		return errors.SignatureError("hash tag doesn't match")
+	}
+
+	if pk.PubKeyAlgo != sig.PubKeyAlgo {
+		return errors.InvalidArgumentError("public key and signature use different algorithms")
+	}
+
+	switch pk.PubKeyAlgo {
+	case PubKeyAlgoRSA, PubKeyAlgoRSASignOnly:
+		rsaPublicKey, _ := pk.PublicKey.(*rsa.PublicKey)
+		err = rsa.VerifyPKCS1v15(rsaPublicKey, sig.Hash, hashBytes, padToKeySize(rsaPublicKey, sig.RSASignature.Bytes()))
+		if err != nil {
+			return errors.SignatureError("RSA verification failure")
+		}
+		return nil
+	case PubKeyAlgoDSA:
+		dsaPublicKey, _ := pk.PublicKey.(*dsa.PublicKey)
+		// Need to truncate hashBytes to match FIPS 186-3 section 4.6.
+		subgroupSize := (dsaPublicKey.Q.BitLen() + 7) / 8
+		if len(hashBytes) > subgroupSize {
+			hashBytes = hashBytes[:subgroupSize]
+		}
+		if !dsa.Verify(dsaPublicKey, hashBytes, new(big.Int).SetBytes(sig.DSASigR.Bytes()), new(big.Int).SetBytes(sig.DSASigS.Bytes())) {
+			return errors.SignatureError("DSA verification failure")
+		}
+		return nil
+	case PubKeyAlgoECDSA:
+		ecdsaPublicKey := pk.PublicKey.(*ecdsa.PublicKey)
+		if !ecdsa.Verify(ecdsaPublicKey, hashBytes, new(big.Int).SetBytes(sig.ECDSASigR.Bytes()), new(big.Int).SetBytes(sig.ECDSASigS.Bytes())) {
+			return errors.SignatureError("ECDSA verification failure")
+		}
+		return nil
+	case PubKeyAlgoEdDSA:
+		eddsaPublicKey := pk.PublicKey.(*eddsa.PublicKey)
+		if !eddsa.Verify(eddsaPublicKey, hashBytes, sig.EdDSASigR.Bytes(), sig.EdDSASigS.Bytes()) {
+			return errors.SignatureError("EdDSA verification failure")
+		}
+		return nil
+	default:
+		return errors.SignatureError("Unsupported public key algorithm used in signature")
+	}
+}
+
+// keySignatureHash returns a Hash of the message that needs to be signed for
+// pk to assert a subkey relationship to signed.
+func keySignatureHash(pk, signed signingKey, hashFunc crypto.Hash) (h hash.Hash, err error) {
+	if !hashFunc.Available() {
+		return nil, errors.UnsupportedError("hash function")
+	}
+	h = hashFunc.New()
+
+	// RFC 4880, section 5.2.4
+	err = pk.SerializeForHash(h)
+	if err != nil {
+		return nil, err
+	}
+
+	err = signed.SerializeForHash(h)
+	return
+}
+
+// VerifyKeySignature returns nil iff sig is a valid signature, made by this
+// public key, of signed.
+func (pk *PublicKey) VerifyKeySignature(signed *PublicKey, sig *Signature) error {
+	h, err := keySignatureHash(pk, signed, sig.Hash)
+	if err != nil {
+		return err
+	}
+	if err = pk.VerifySignature(h, sig); err != nil {
+		return err
+	}
+
+	if sig.FlagSign {
+		// Signing subkeys must be cross-signed. See
+		// https://www.gnupg.org/faq/subkey-cross-certify.html.
+		if sig.EmbeddedSignature == nil {
+			return errors.StructuralError("signing subkey is missing cross-signature")
+		}
+		// Verify the cross-signature. This is calculated over the same
+		// data as the main signature, so we cannot just recursively
+		// call signed.VerifyKeySignature(...)
+		if h, err = keySignatureHash(pk, signed, sig.EmbeddedSignature.Hash); err != nil {
+			return errors.StructuralError("error while hashing for cross-signature: " + err.Error())
+		}
+		if err := signed.VerifySignature(h, sig.EmbeddedSignature); err != nil {
+			return errors.StructuralError("error while verifying cross-signature: " + err.Error())
+		}
+	}
+
+	return nil
+}
+
+func keyRevocationHash(pk signingKey, hashFunc crypto.Hash) (h hash.Hash, err error) {
+	if !hashFunc.Available() {
+		return nil, errors.UnsupportedError("hash function")
+	}
+	h = hashFunc.New()
+
+	// RFC 4880, section 5.2.4
+	err = pk.SerializeForHash(h)
+
+	return
+}
+
+// VerifyRevocationSignature returns nil iff sig is a valid signature, made by this
+// public key.
+func (pk *PublicKey) VerifyRevocationSignature(sig *Signature) (err error) {
+	h, err := keyRevocationHash(pk, sig.Hash)
+	if err != nil {
+		return err
+	}
+	return pk.VerifySignature(h, sig)
+}
+
+// VerifySubkeyRevocationSignature returns nil iff sig is a valid subkey revocation signature,
+// made by this public key, of signed.
+func (pk *PublicKey) VerifySubkeyRevocationSignature(sig *Signature, signed *PublicKey) (err error) {
+	h, err := keySignatureHash(pk, signed, sig.Hash)
+	if err != nil {
+		return err
+	}
+	return pk.VerifySignature(h, sig)
+}
+
+// userIdSignatureHash returns a Hash of the message that needs to be signed
+// to assert that pk is a valid key for id.
+func userIdSignatureHash(id string, pk *PublicKey, hashFunc crypto.Hash) (h hash.Hash, err error) {
+	if !hashFunc.Available() {
+		return nil, errors.UnsupportedError("hash function")
+	}
+	h = hashFunc.New()
+
+	// RFC 4880, section 5.2.4
+	pk.SerializeSignaturePrefix(h)
+	pk.serializeWithoutHeaders(h)
+
+	var buf [5]byte
+	buf[0] = 0xb4
+	buf[1] = byte(len(id) >> 24)
+	buf[2] = byte(len(id) >> 16)
+	buf[3] = byte(len(id) >> 8)
+	buf[4] = byte(len(id))
+	h.Write(buf[:])
+	h.Write([]byte(id))
+
+	return
+}
+
+// VerifyUserIdSignature returns nil iff sig is a valid signature, made by this
+// public key, that id is the identity of pub.
+func (pk *PublicKey) VerifyUserIdSignature(id string, pub *PublicKey, sig *Signature) (err error) {
+	h, err := userIdSignatureHash(id, pub, sig.Hash)
+	if err != nil {
+		return err
+	}
+	return pk.VerifySignature(h, sig)
+}
+
+// KeyIdString returns the public key's fingerprint in capital hex
+// (e.g. "6C7EE1B8621CC013").
+func (pk *PublicKey) KeyIdString() string {
+	return fmt.Sprintf("%X", pk.Fingerprint[12:20])
+}
+
+// KeyIdShortString returns the short form of public key's fingerprint
+// in capital hex, as shown by gpg --list-keys (e.g. "621CC013").
+func (pk *PublicKey) KeyIdShortString() string {
+	return fmt.Sprintf("%X", pk.Fingerprint[16:20])
+}
+
+// BitLength returns the bit length for the given public key.
+func (pk *PublicKey) BitLength() (bitLength uint16, err error) {
+	switch pk.PubKeyAlgo {
+	case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly, PubKeyAlgoRSASignOnly:
+		bitLength = pk.n.BitLength()
+	case PubKeyAlgoDSA:
+		bitLength = pk.p.BitLength()
+	case PubKeyAlgoElGamal:
+		bitLength = pk.p.BitLength()
+	case PubKeyAlgoECDSA:
+		bitLength = pk.p.BitLength()
+	case PubKeyAlgoECDH:
+		bitLength = pk.p.BitLength()
+	case PubKeyAlgoEdDSA:
+		bitLength = pk.p.BitLength()
+	default:
+		err = errors.InvalidArgumentError("bad public-key algorithm")
+	}
+	return
+}
+
+// KeyExpired returns whether sig is a self-signature of a key that has
+// expired or is created in the future.
+func (pk *PublicKey) KeyExpired(sig *Signature, currentTime time.Time) bool {
+	if pk.CreationTime.After(currentTime) {
+		return true
+	}
+	if sig.KeyLifetimeSecs == nil || *sig.KeyLifetimeSecs == 0 {
+		return false
+	}
+	expiry := pk.CreationTime.Add(time.Duration(*sig.KeyLifetimeSecs) * time.Second)
+	return currentTime.After(expiry)
+}