tea/vendor/github.com/ProtonMail/go-crypto/openpgp/packet/signature.go

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// 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 (
"bytes"
"crypto"
"crypto/dsa"
"crypto/ecdsa"
"encoding/asn1"
"encoding/binary"
"hash"
"io"
"math/big"
"strconv"
"time"
"github.com/ProtonMail/go-crypto/openpgp/errors"
"github.com/ProtonMail/go-crypto/openpgp/internal/encoding"
"github.com/ProtonMail/go-crypto/openpgp/s2k"
)
const (
// See RFC 4880, section 5.2.3.21 for details.
KeyFlagCertify = 1 << iota
KeyFlagSign
KeyFlagEncryptCommunications
KeyFlagEncryptStorage
)
// Signature represents a signature. See RFC 4880, section 5.2.
type Signature struct {
Version int
SigType SignatureType
PubKeyAlgo PublicKeyAlgorithm
Hash crypto.Hash
// HashSuffix is extra data that is hashed in after the signed data.
HashSuffix []byte
// HashTag contains the first two bytes of the hash for fast rejection
// of bad signed data.
HashTag [2]byte
// Metadata includes format, filename and time, and is protected by v5
// signatures of type 0x00 or 0x01. This metadata is included into the hash
// computation; if nil, six 0x00 bytes are used instead. See section 5.2.4.
Metadata *LiteralData
CreationTime time.Time
RSASignature encoding.Field
DSASigR, DSASigS encoding.Field
ECDSASigR, ECDSASigS encoding.Field
EdDSASigR, EdDSASigS encoding.Field
// rawSubpackets contains the unparsed subpackets, in order.
rawSubpackets []outputSubpacket
// The following are optional so are nil when not included in the
// signature.
SigLifetimeSecs, KeyLifetimeSecs *uint32
PreferredSymmetric, PreferredHash, PreferredCompression []uint8
PreferredAEAD []uint8
IssuerKeyId *uint64
IssuerFingerprint []byte
IsPrimaryId *bool
// PolicyURI can be set to the URI of a document that describes the
// policy under which the signature was issued. See RFC 4880, section
// 5.2.3.20 for details.
PolicyURI string
// FlagsValid is set if any flags were given. See RFC 4880, section
// 5.2.3.21 for details.
FlagsValid bool
FlagCertify, FlagSign, FlagEncryptCommunications, FlagEncryptStorage bool
// RevocationReason is set if this signature has been revoked.
// See RFC 4880, section 5.2.3.23 for details.
RevocationReason *uint8
RevocationReasonText string
// In a self-signature, these flags are set there is a features subpacket
// indicating that the issuer implementation supports these features
// (section 5.2.5.25).
MDC, AEAD, V5Keys bool
// EmbeddedSignature, if non-nil, is a signature of the parent key, by
// this key. This prevents an attacker from claiming another's signing
// subkey as their own.
EmbeddedSignature *Signature
outSubpackets []outputSubpacket
}
func (sig *Signature) parse(r io.Reader) (err error) {
// RFC 4880, section 5.2.3
var buf [5]byte
_, err = readFull(r, buf[:1])
if err != nil {
return
}
if buf[0] != 4 && buf[0] != 5 {
err = errors.UnsupportedError("signature packet version " + strconv.Itoa(int(buf[0])))
return
}
sig.Version = int(buf[0])
_, err = readFull(r, buf[:5])
if err != nil {
return
}
sig.SigType = SignatureType(buf[0])
sig.PubKeyAlgo = PublicKeyAlgorithm(buf[1])
switch sig.PubKeyAlgo {
case PubKeyAlgoRSA, PubKeyAlgoRSASignOnly, PubKeyAlgoDSA, PubKeyAlgoECDSA, PubKeyAlgoEdDSA:
default:
err = errors.UnsupportedError("public key algorithm " + strconv.Itoa(int(sig.PubKeyAlgo)))
return
}
var ok bool
sig.Hash, ok = s2k.HashIdToHash(buf[2])
if !ok {
return errors.UnsupportedError("hash function " + strconv.Itoa(int(buf[2])))
}
hashedSubpacketsLength := int(buf[3])<<8 | int(buf[4])
hashedSubpackets := make([]byte, hashedSubpacketsLength)
_, err = readFull(r, hashedSubpackets)
if err != nil {
return
}
sig.buildHashSuffix(hashedSubpackets)
err = parseSignatureSubpackets(sig, hashedSubpackets, true)
if err != nil {
return
}
_, err = readFull(r, buf[:2])
if err != nil {
return
}
unhashedSubpacketsLength := int(buf[0])<<8 | int(buf[1])
unhashedSubpackets := make([]byte, unhashedSubpacketsLength)
_, err = readFull(r, unhashedSubpackets)
if err != nil {
return
}
err = parseSignatureSubpackets(sig, unhashedSubpackets, false)
if err != nil {
return
}
_, err = readFull(r, sig.HashTag[:2])
if err != nil {
return
}
switch sig.PubKeyAlgo {
case PubKeyAlgoRSA, PubKeyAlgoRSASignOnly:
sig.RSASignature = new(encoding.MPI)
_, err = sig.RSASignature.ReadFrom(r)
case PubKeyAlgoDSA:
sig.DSASigR = new(encoding.MPI)
if _, err = sig.DSASigR.ReadFrom(r); err != nil {
return
}
sig.DSASigS = new(encoding.MPI)
_, err = sig.DSASigS.ReadFrom(r)
case PubKeyAlgoECDSA:
sig.ECDSASigR = new(encoding.MPI)
if _, err = sig.ECDSASigR.ReadFrom(r); err != nil {
return
}
sig.ECDSASigS = new(encoding.MPI)
_, err = sig.ECDSASigS.ReadFrom(r)
case PubKeyAlgoEdDSA:
sig.EdDSASigR = new(encoding.MPI)
if _, err = sig.EdDSASigR.ReadFrom(r); err != nil {
return
}
sig.EdDSASigS = new(encoding.MPI)
if _, err = sig.EdDSASigS.ReadFrom(r); err != nil {
return
}
default:
panic("unreachable")
}
return
}
// parseSignatureSubpackets parses subpackets of the main signature packet. See
// RFC 4880, section 5.2.3.1.
func parseSignatureSubpackets(sig *Signature, subpackets []byte, isHashed bool) (err error) {
for len(subpackets) > 0 {
subpackets, err = parseSignatureSubpacket(sig, subpackets, isHashed)
if err != nil {
return
}
}
if sig.CreationTime.IsZero() {
err = errors.StructuralError("no creation time in signature")
}
return
}
type signatureSubpacketType uint8
const (
creationTimeSubpacket signatureSubpacketType = 2
signatureExpirationSubpacket signatureSubpacketType = 3
keyExpirationSubpacket signatureSubpacketType = 9
prefSymmetricAlgosSubpacket signatureSubpacketType = 11
issuerSubpacket signatureSubpacketType = 16
prefHashAlgosSubpacket signatureSubpacketType = 21
prefCompressionSubpacket signatureSubpacketType = 22
primaryUserIdSubpacket signatureSubpacketType = 25
policyUriSubpacket signatureSubpacketType = 26
keyFlagsSubpacket signatureSubpacketType = 27
reasonForRevocationSubpacket signatureSubpacketType = 29
featuresSubpacket signatureSubpacketType = 30
embeddedSignatureSubpacket signatureSubpacketType = 32
issuerFingerprintSubpacket signatureSubpacketType = 33
prefAeadAlgosSubpacket signatureSubpacketType = 34
)
// parseSignatureSubpacket parses a single subpacket. len(subpacket) is >= 1.
func parseSignatureSubpacket(sig *Signature, subpacket []byte, isHashed bool) (rest []byte, err error) {
// RFC 4880, section 5.2.3.1
var (
length uint32
packetType signatureSubpacketType
isCritical bool
)
switch {
case subpacket[0] < 192:
length = uint32(subpacket[0])
subpacket = subpacket[1:]
case subpacket[0] < 255:
if len(subpacket) < 2 {
goto Truncated
}
length = uint32(subpacket[0]-192)<<8 + uint32(subpacket[1]) + 192
subpacket = subpacket[2:]
default:
if len(subpacket) < 5 {
goto Truncated
}
length = uint32(subpacket[1])<<24 |
uint32(subpacket[2])<<16 |
uint32(subpacket[3])<<8 |
uint32(subpacket[4])
subpacket = subpacket[5:]
}
if length > uint32(len(subpacket)) {
goto Truncated
}
rest = subpacket[length:]
subpacket = subpacket[:length]
if len(subpacket) == 0 {
err = errors.StructuralError("zero length signature subpacket")
return
}
packetType = signatureSubpacketType(subpacket[0] & 0x7f)
isCritical = subpacket[0]&0x80 == 0x80
subpacket = subpacket[1:]
sig.rawSubpackets = append(sig.rawSubpackets, outputSubpacket{isHashed, packetType, isCritical, subpacket})
switch packetType {
case creationTimeSubpacket:
if !isHashed {
err = errors.StructuralError("signature creation time in non-hashed area")
return
}
if len(subpacket) != 4 {
err = errors.StructuralError("signature creation time not four bytes")
return
}
t := binary.BigEndian.Uint32(subpacket)
sig.CreationTime = time.Unix(int64(t), 0)
case signatureExpirationSubpacket:
// Signature expiration time, section 5.2.3.10
if !isHashed {
return
}
if len(subpacket) != 4 {
err = errors.StructuralError("expiration subpacket with bad length")
return
}
sig.SigLifetimeSecs = new(uint32)
*sig.SigLifetimeSecs = binary.BigEndian.Uint32(subpacket)
case keyExpirationSubpacket:
// Key expiration time, section 5.2.3.6
if !isHashed {
return
}
if len(subpacket) != 4 {
err = errors.StructuralError("key expiration subpacket with bad length")
return
}
sig.KeyLifetimeSecs = new(uint32)
*sig.KeyLifetimeSecs = binary.BigEndian.Uint32(subpacket)
case prefSymmetricAlgosSubpacket:
// Preferred symmetric algorithms, section 5.2.3.7
if !isHashed {
return
}
sig.PreferredSymmetric = make([]byte, len(subpacket))
copy(sig.PreferredSymmetric, subpacket)
case issuerSubpacket:
if sig.Version > 4 {
err = errors.StructuralError("issuer subpacket found in v5 key")
}
// Issuer, section 5.2.3.5
if len(subpacket) != 8 {
err = errors.StructuralError("issuer subpacket with bad length")
return
}
sig.IssuerKeyId = new(uint64)
*sig.IssuerKeyId = binary.BigEndian.Uint64(subpacket)
case prefHashAlgosSubpacket:
// Preferred hash algorithms, section 5.2.3.8
if !isHashed {
return
}
sig.PreferredHash = make([]byte, len(subpacket))
copy(sig.PreferredHash, subpacket)
case prefCompressionSubpacket:
// Preferred compression algorithms, section 5.2.3.9
if !isHashed {
return
}
sig.PreferredCompression = make([]byte, len(subpacket))
copy(sig.PreferredCompression, subpacket)
case primaryUserIdSubpacket:
// Primary User ID, section 5.2.3.19
if !isHashed {
return
}
if len(subpacket) != 1 {
err = errors.StructuralError("primary user id subpacket with bad length")
return
}
sig.IsPrimaryId = new(bool)
if subpacket[0] > 0 {
*sig.IsPrimaryId = true
}
case keyFlagsSubpacket:
// Key flags, section 5.2.3.21
if !isHashed {
return
}
if len(subpacket) == 0 {
err = errors.StructuralError("empty key flags subpacket")
return
}
sig.FlagsValid = true
if subpacket[0]&KeyFlagCertify != 0 {
sig.FlagCertify = true
}
if subpacket[0]&KeyFlagSign != 0 {
sig.FlagSign = true
}
if subpacket[0]&KeyFlagEncryptCommunications != 0 {
sig.FlagEncryptCommunications = true
}
if subpacket[0]&KeyFlagEncryptStorage != 0 {
sig.FlagEncryptStorage = true
}
case reasonForRevocationSubpacket:
// Reason For Revocation, section 5.2.3.23
if !isHashed {
return
}
if len(subpacket) == 0 {
err = errors.StructuralError("empty revocation reason subpacket")
return
}
sig.RevocationReason = new(uint8)
*sig.RevocationReason = subpacket[0]
sig.RevocationReasonText = string(subpacket[1:])
case featuresSubpacket:
// Features subpacket, section 5.2.3.24 specifies a very general
// mechanism for OpenPGP implementations to signal support for new
// features.
if !isHashed {
return
}
if len(subpacket) > 0 {
if subpacket[0]&0x01 != 0 {
sig.MDC = true
}
if subpacket[0]&0x02 != 0 {
sig.AEAD = true
}
if subpacket[0]&0x04 != 0 {
sig.V5Keys = true
}
}
case embeddedSignatureSubpacket:
// Only usage is in signatures that cross-certify
// signing subkeys. section 5.2.3.26 describes the
// format, with its usage described in section 11.1
if sig.EmbeddedSignature != nil {
err = errors.StructuralError("Cannot have multiple embedded signatures")
return
}
sig.EmbeddedSignature = new(Signature)
// Embedded signatures are required to be v4 signatures see
// section 12.1. However, we only parse v4 signatures in this
// file anyway.
if err := sig.EmbeddedSignature.parse(bytes.NewBuffer(subpacket)); err != nil {
return nil, err
}
if sigType := sig.EmbeddedSignature.SigType; sigType != SigTypePrimaryKeyBinding {
return nil, errors.StructuralError("cross-signature has unexpected type " + strconv.Itoa(int(sigType)))
}
case policyUriSubpacket:
// Policy URI, section 5.2.3.20
if !isHashed {
return
}
sig.PolicyURI = string(subpacket)
case issuerFingerprintSubpacket:
v, l := subpacket[0], len(subpacket[1:])
if v == 5 && l != 32 || v != 5 && l != 20 {
return nil, errors.StructuralError("bad fingerprint length")
}
sig.IssuerFingerprint = make([]byte, l)
copy(sig.IssuerFingerprint, subpacket[1:])
sig.IssuerKeyId = new(uint64)
if v == 5 {
*sig.IssuerKeyId = binary.BigEndian.Uint64(subpacket[1:9])
} else {
*sig.IssuerKeyId = binary.BigEndian.Uint64(subpacket[13:21])
}
case prefAeadAlgosSubpacket:
// Preferred symmetric algorithms, section 5.2.3.8
if !isHashed {
return
}
sig.PreferredAEAD = make([]byte, len(subpacket))
copy(sig.PreferredAEAD, subpacket)
default:
if isCritical {
err = errors.UnsupportedError("unknown critical signature subpacket type " + strconv.Itoa(int(packetType)))
return
}
}
return
Truncated:
err = errors.StructuralError("signature subpacket truncated")
return
}
// subpacketLengthLength returns the length, in bytes, of an encoded length value.
func subpacketLengthLength(length int) int {
if length < 192 {
return 1
}
if length < 16320 {
return 2
}
return 5
}
func (sig *Signature) CheckKeyIdOrFingerprint(pk *PublicKey) bool {
if sig.IssuerFingerprint != nil && len(sig.IssuerFingerprint) >= 20 {
return bytes.Equal(sig.IssuerFingerprint, pk.Fingerprint)
}
return sig.IssuerKeyId != nil && *sig.IssuerKeyId == pk.KeyId
}
// serializeSubpacketLength marshals the given length into to.
func serializeSubpacketLength(to []byte, length int) int {
// RFC 4880, Section 4.2.2.
if length < 192 {
to[0] = byte(length)
return 1
}
if length < 16320 {
length -= 192
to[0] = byte((length >> 8) + 192)
to[1] = byte(length)
return 2
}
to[0] = 255
to[1] = byte(length >> 24)
to[2] = byte(length >> 16)
to[3] = byte(length >> 8)
to[4] = byte(length)
return 5
}
// subpacketsLength returns the serialized length, in bytes, of the given
// subpackets.
func subpacketsLength(subpackets []outputSubpacket, hashed bool) (length int) {
for _, subpacket := range subpackets {
if subpacket.hashed == hashed {
length += subpacketLengthLength(len(subpacket.contents) + 1)
length += 1 // type byte
length += len(subpacket.contents)
}
}
return
}
// serializeSubpackets marshals the given subpackets into to.
func serializeSubpackets(to []byte, subpackets []outputSubpacket, hashed bool) {
for _, subpacket := range subpackets {
if subpacket.hashed == hashed {
n := serializeSubpacketLength(to, len(subpacket.contents)+1)
to[n] = byte(subpacket.subpacketType)
if subpacket.isCritical {
to[n] |= 0x80
}
to = to[1+n:]
n = copy(to, subpacket.contents)
to = to[n:]
}
}
return
}
// SigExpired returns whether sig is a signature that has expired or is created
// in the future.
func (sig *Signature) SigExpired(currentTime time.Time) bool {
if sig.CreationTime.After(currentTime) {
return true
}
if sig.SigLifetimeSecs == nil || *sig.SigLifetimeSecs == 0 {
return false
}
expiry := sig.CreationTime.Add(time.Duration(*sig.SigLifetimeSecs) * time.Second)
return currentTime.After(expiry)
}
// buildHashSuffix constructs the HashSuffix member of sig in preparation for signing.
func (sig *Signature) buildHashSuffix(hashedSubpackets []byte) (err error) {
hash, ok := s2k.HashToHashId(sig.Hash)
if !ok {
sig.HashSuffix = nil
return errors.InvalidArgumentError("hash cannot be represented in OpenPGP: " + strconv.Itoa(int(sig.Hash)))
}
hashedFields := bytes.NewBuffer([]byte{
uint8(sig.Version),
uint8(sig.SigType),
uint8(sig.PubKeyAlgo),
uint8(hash),
uint8(len(hashedSubpackets) >> 8),
uint8(len(hashedSubpackets)),
})
hashedFields.Write(hashedSubpackets)
var l uint64 = uint64(6 + len(hashedSubpackets))
if sig.Version == 5 {
hashedFields.Write([]byte{0x05, 0xff})
hashedFields.Write([]byte{
uint8(l >> 56), uint8(l >> 48), uint8(l >> 40), uint8(l >> 32),
uint8(l >> 24), uint8(l >> 16), uint8(l >> 8), uint8(l),
})
} else {
hashedFields.Write([]byte{0x04, 0xff})
hashedFields.Write([]byte{
uint8(l >> 24), uint8(l >> 16), uint8(l >> 8), uint8(l),
})
}
sig.HashSuffix = make([]byte, hashedFields.Len())
copy(sig.HashSuffix, hashedFields.Bytes())
return
}
func (sig *Signature) signPrepareHash(h hash.Hash) (digest []byte, err error) {
hashedSubpacketsLen := subpacketsLength(sig.outSubpackets, true)
hashedSubpackets := make([]byte, hashedSubpacketsLen)
serializeSubpackets(hashedSubpackets, sig.outSubpackets, true)
err = sig.buildHashSuffix(hashedSubpackets)
if err != nil {
return
}
if sig.Version == 5 && (sig.SigType == 0x00 || sig.SigType == 0x01) {
sig.AddMetadataToHashSuffix()
}
h.Write(sig.HashSuffix)
digest = h.Sum(nil)
copy(sig.HashTag[:], digest)
return
}
// Sign signs a message with a private key. The hash, h, must contain
// the hash of the message to be signed and will be mutated by this function.
// On success, the signature is stored in sig. Call Serialize to write it out.
// If config is nil, sensible defaults will be used.
func (sig *Signature) Sign(h hash.Hash, priv *PrivateKey, config *Config) (err error) {
if priv.Dummy() {
return errors.ErrDummyPrivateKey("dummy key found")
}
sig.Version = priv.PublicKey.Version
sig.IssuerFingerprint = priv.PublicKey.Fingerprint
sig.outSubpackets, err = sig.buildSubpackets(priv.PublicKey)
if err != nil {
return err
}
digest, err := sig.signPrepareHash(h)
if err != nil {
return
}
switch priv.PubKeyAlgo {
case PubKeyAlgoRSA, PubKeyAlgoRSASignOnly:
// supports both *rsa.PrivateKey and crypto.Signer
sigdata, err := priv.PrivateKey.(crypto.Signer).Sign(config.Random(), digest, sig.Hash)
if err == nil {
sig.RSASignature = encoding.NewMPI(sigdata)
}
case PubKeyAlgoDSA:
dsaPriv := priv.PrivateKey.(*dsa.PrivateKey)
// Need to truncate hashBytes to match FIPS 186-3 section 4.6.
subgroupSize := (dsaPriv.Q.BitLen() + 7) / 8
if len(digest) > subgroupSize {
digest = digest[:subgroupSize]
}
r, s, err := dsa.Sign(config.Random(), dsaPriv, digest)
if err == nil {
sig.DSASigR = new(encoding.MPI).SetBig(r)
sig.DSASigS = new(encoding.MPI).SetBig(s)
}
case PubKeyAlgoECDSA:
var r, s *big.Int
if pk, ok := priv.PrivateKey.(*ecdsa.PrivateKey); ok {
// direct support, avoid asn1 wrapping/unwrapping
r, s, err = ecdsa.Sign(config.Random(), pk, digest)
} else {
var b []byte
b, err = priv.PrivateKey.(crypto.Signer).Sign(config.Random(), digest, sig.Hash)
if err == nil {
r, s, err = unwrapECDSASig(b)
}
}
if err == nil {
sig.ECDSASigR = new(encoding.MPI).SetBig(r)
sig.ECDSASigS = new(encoding.MPI).SetBig(s)
}
case PubKeyAlgoEdDSA:
sigdata, err := priv.PrivateKey.(crypto.Signer).Sign(config.Random(), digest, crypto.Hash(0))
if err == nil {
sig.EdDSASigR = encoding.NewMPI(sigdata[:32])
sig.EdDSASigS = encoding.NewMPI(sigdata[32:])
}
default:
err = errors.UnsupportedError("public key algorithm: " + strconv.Itoa(int(sig.PubKeyAlgo)))
}
return
}
// unwrapECDSASig parses the two integer components of an ASN.1-encoded ECDSA
// signature.
func unwrapECDSASig(b []byte) (r, s *big.Int, err error) {
var ecsdaSig struct {
R, S *big.Int
}
_, err = asn1.Unmarshal(b, &ecsdaSig)
if err != nil {
return
}
return ecsdaSig.R, ecsdaSig.S, nil
}
// SignUserId computes a signature from priv, asserting that pub is a valid
// key for the identity id. On success, the signature is stored in sig. Call
// Serialize to write it out.
// If config is nil, sensible defaults will be used.
func (sig *Signature) SignUserId(id string, pub *PublicKey, priv *PrivateKey, config *Config) error {
if priv.Dummy() {
return errors.ErrDummyPrivateKey("dummy key found")
}
h, err := userIdSignatureHash(id, pub, sig.Hash)
if err != nil {
return err
}
return sig.Sign(h, priv, config)
}
// CrossSignKey computes a signature from signingKey on pub hashed using hashKey. On success,
// the signature is stored in sig. Call Serialize to write it out.
// If config is nil, sensible defaults will be used.
func (sig *Signature) CrossSignKey(pub *PublicKey, hashKey *PublicKey, signingKey *PrivateKey,
config *Config) error {
h, err := keySignatureHash(hashKey, pub, sig.Hash)
if err != nil {
return err
}
return sig.Sign(h, signingKey, config)
}
// SignKey computes a signature from priv, asserting that pub is a subkey. On
// success, the signature is stored in sig. Call Serialize to write it out.
// If config is nil, sensible defaults will be used.
func (sig *Signature) SignKey(pub *PublicKey, priv *PrivateKey, config *Config) error {
if priv.Dummy() {
return errors.ErrDummyPrivateKey("dummy key found")
}
h, err := keySignatureHash(&priv.PublicKey, pub, sig.Hash)
if err != nil {
return err
}
return sig.Sign(h, priv, config)
}
// RevokeKey computes a revocation signature of pub using priv. On success, the signature is
// stored in sig. Call Serialize to write it out.
// If config is nil, sensible defaults will be used.
func (sig *Signature) RevokeKey(pub *PublicKey, priv *PrivateKey, config *Config) error {
h, err := keyRevocationHash(pub, sig.Hash)
if err != nil {
return err
}
return sig.Sign(h, priv, config)
}
// Serialize marshals sig to w. Sign, SignUserId or SignKey must have been
// called first.
func (sig *Signature) Serialize(w io.Writer) (err error) {
if len(sig.outSubpackets) == 0 {
sig.outSubpackets = sig.rawSubpackets
}
if sig.RSASignature == nil && sig.DSASigR == nil && sig.ECDSASigR == nil && sig.EdDSASigR == nil {
return errors.InvalidArgumentError("Signature: need to call Sign, SignUserId or SignKey before Serialize")
}
sigLength := 0
switch sig.PubKeyAlgo {
case PubKeyAlgoRSA, PubKeyAlgoRSASignOnly:
sigLength = int(sig.RSASignature.EncodedLength())
case PubKeyAlgoDSA:
sigLength = int(sig.DSASigR.EncodedLength())
sigLength += int(sig.DSASigS.EncodedLength())
case PubKeyAlgoECDSA:
sigLength = int(sig.ECDSASigR.EncodedLength())
sigLength += int(sig.ECDSASigS.EncodedLength())
case PubKeyAlgoEdDSA:
sigLength = int(sig.EdDSASigR.EncodedLength())
sigLength += int(sig.EdDSASigS.EncodedLength())
default:
panic("impossible")
}
unhashedSubpacketsLen := subpacketsLength(sig.outSubpackets, false)
length := len(sig.HashSuffix) - 6 /* trailer not included */ +
2 /* length of unhashed subpackets */ + unhashedSubpacketsLen +
2 /* hash tag */ + sigLength
if sig.Version == 5 {
length -= 4 // eight-octet instead of four-octet big endian
}
err = serializeHeader(w, packetTypeSignature, length)
if err != nil {
return
}
err = sig.serializeBody(w)
if err != nil {
return err
}
return
}
func (sig *Signature) serializeBody(w io.Writer) (err error) {
hashedSubpacketsLen := uint16(uint16(sig.HashSuffix[4])<<8) | uint16(sig.HashSuffix[5])
fields := sig.HashSuffix[:6+hashedSubpacketsLen]
_, err = w.Write(fields)
if err != nil {
return
}
unhashedSubpacketsLen := subpacketsLength(sig.outSubpackets, false)
unhashedSubpackets := make([]byte, 2+unhashedSubpacketsLen)
unhashedSubpackets[0] = byte(unhashedSubpacketsLen >> 8)
unhashedSubpackets[1] = byte(unhashedSubpacketsLen)
serializeSubpackets(unhashedSubpackets[2:], sig.outSubpackets, false)
_, err = w.Write(unhashedSubpackets)
if err != nil {
return
}
_, err = w.Write(sig.HashTag[:])
if err != nil {
return
}
switch sig.PubKeyAlgo {
case PubKeyAlgoRSA, PubKeyAlgoRSASignOnly:
_, err = w.Write(sig.RSASignature.EncodedBytes())
case PubKeyAlgoDSA:
if _, err = w.Write(sig.DSASigR.EncodedBytes()); err != nil {
return
}
_, err = w.Write(sig.DSASigS.EncodedBytes())
case PubKeyAlgoECDSA:
if _, err = w.Write(sig.ECDSASigR.EncodedBytes()); err != nil {
return
}
_, err = w.Write(sig.ECDSASigS.EncodedBytes())
case PubKeyAlgoEdDSA:
if _, err = w.Write(sig.EdDSASigR.EncodedBytes()); err != nil {
return
}
_, err = w.Write(sig.EdDSASigS.EncodedBytes())
default:
panic("impossible")
}
return
}
// outputSubpacket represents a subpacket to be marshaled.
type outputSubpacket struct {
hashed bool // true if this subpacket is in the hashed area.
subpacketType signatureSubpacketType
isCritical bool
contents []byte
}
func (sig *Signature) buildSubpackets(issuer PublicKey) (subpackets []outputSubpacket, err error) {
creationTime := make([]byte, 4)
binary.BigEndian.PutUint32(creationTime, uint32(sig.CreationTime.Unix()))
subpackets = append(subpackets, outputSubpacket{true, creationTimeSubpacket, false, creationTime})
if sig.IssuerKeyId != nil && sig.Version == 4 {
keyId := make([]byte, 8)
binary.BigEndian.PutUint64(keyId, *sig.IssuerKeyId)
subpackets = append(subpackets, outputSubpacket{true, issuerSubpacket, true, keyId})
}
if sig.IssuerFingerprint != nil {
contents := append([]uint8{uint8(issuer.Version)}, sig.IssuerFingerprint...)
subpackets = append(subpackets, outputSubpacket{true, issuerFingerprintSubpacket, true, contents})
}
if sig.SigLifetimeSecs != nil && *sig.SigLifetimeSecs != 0 {
sigLifetime := make([]byte, 4)
binary.BigEndian.PutUint32(sigLifetime, *sig.SigLifetimeSecs)
subpackets = append(subpackets, outputSubpacket{true, signatureExpirationSubpacket, true, sigLifetime})
}
// Key flags may only appear in self-signatures or certification signatures.
if sig.FlagsValid {
var flags byte
if sig.FlagCertify {
flags |= KeyFlagCertify
}
if sig.FlagSign {
flags |= KeyFlagSign
}
if sig.FlagEncryptCommunications {
flags |= KeyFlagEncryptCommunications
}
if sig.FlagEncryptStorage {
flags |= KeyFlagEncryptStorage
}
subpackets = append(subpackets, outputSubpacket{true, keyFlagsSubpacket, false, []byte{flags}})
}
// The following subpackets may only appear in self-signatures.
var features = byte(0x00)
if sig.MDC {
features |= 0x01
}
if sig.AEAD {
features |= 0x02
}
if sig.V5Keys {
features |= 0x04
}
if features != 0x00 {
subpackets = append(subpackets, outputSubpacket{true, featuresSubpacket, false, []byte{features}})
}
if sig.KeyLifetimeSecs != nil && *sig.KeyLifetimeSecs != 0 {
keyLifetime := make([]byte, 4)
binary.BigEndian.PutUint32(keyLifetime, *sig.KeyLifetimeSecs)
subpackets = append(subpackets, outputSubpacket{true, keyExpirationSubpacket, true, keyLifetime})
}
if sig.IsPrimaryId != nil && *sig.IsPrimaryId {
subpackets = append(subpackets, outputSubpacket{true, primaryUserIdSubpacket, false, []byte{1}})
}
if len(sig.PreferredSymmetric) > 0 {
subpackets = append(subpackets, outputSubpacket{true, prefSymmetricAlgosSubpacket, false, sig.PreferredSymmetric})
}
if len(sig.PreferredHash) > 0 {
subpackets = append(subpackets, outputSubpacket{true, prefHashAlgosSubpacket, false, sig.PreferredHash})
}
if len(sig.PreferredCompression) > 0 {
subpackets = append(subpackets, outputSubpacket{true, prefCompressionSubpacket, false, sig.PreferredCompression})
}
if len(sig.PolicyURI) > 0 {
subpackets = append(subpackets, outputSubpacket{true, policyUriSubpacket, false, []uint8(sig.PolicyURI)})
}
if len(sig.PreferredAEAD) > 0 {
subpackets = append(subpackets, outputSubpacket{true, prefAeadAlgosSubpacket, false, sig.PreferredAEAD})
}
// Revocation reason appears only in revocation signatures and is serialized as per section 5.2.3.23.
if sig.RevocationReason != nil {
subpackets = append(subpackets, outputSubpacket{true, reasonForRevocationSubpacket, true,
append([]uint8{*sig.RevocationReason}, []uint8(sig.RevocationReasonText)...)})
}
// EmbeddedSignature appears only in subkeys capable of signing and is serialized as per section 5.2.3.26.
if sig.EmbeddedSignature != nil {
var buf bytes.Buffer
err = sig.EmbeddedSignature.serializeBody(&buf)
if err != nil {
return
}
subpackets = append(subpackets, outputSubpacket{true, embeddedSignatureSubpacket, true, buf.Bytes()})
}
return
}
// AddMetadataToHashSuffix modifies the current hash suffix to include metadata
// (format, filename, and time). Version 5 keys protect this data including it
// in the hash computation. See section 5.2.4.
func (sig *Signature) AddMetadataToHashSuffix() {
if sig == nil || sig.Version != 5 {
return
}
if sig.SigType != 0x00 && sig.SigType != 0x01 {
return
}
lit := sig.Metadata
if lit == nil {
// This will translate into six 0x00 bytes.
lit = &LiteralData{}
}
// Extract the current byte count
n := sig.HashSuffix[len(sig.HashSuffix)-8:]
l := uint64(
uint64(n[0])<<56 | uint64(n[1])<<48 | uint64(n[2])<<40 | uint64(n[3])<<32 |
uint64(n[4])<<24 | uint64(n[5])<<16 | uint64(n[6])<<8 | uint64(n[7]))
suffix := bytes.NewBuffer(nil)
suffix.Write(sig.HashSuffix[:l])
// Add the metadata
var buf [4]byte
buf[0] = lit.Format
fileName := lit.FileName
if len(lit.FileName) > 255 {
fileName = fileName[:255]
}
buf[1] = byte(len(fileName))
suffix.Write(buf[:2])
suffix.Write([]byte(lit.FileName))
binary.BigEndian.PutUint32(buf[:], lit.Time)
suffix.Write(buf[:])
// Update the counter and restore trailing bytes
l = uint64(suffix.Len())
suffix.Write([]byte{0x05, 0xff})
suffix.Write([]byte{
uint8(l >> 56), uint8(l >> 48), uint8(l >> 40), uint8(l >> 32),
uint8(l >> 24), uint8(l >> 16), uint8(l >> 8), uint8(l),
})
sig.HashSuffix = suffix.Bytes()
}