func addSubkey(e *Entity, packets *packet.Reader, pub *packet.PublicKey, priv *packet.PrivateKey) error {
var subKey Subkey
subKey.PublicKey = pub
subKey.PrivateKey = priv
p, err := packets.Next()
if err == io.EOF {
return io.ErrUnexpectedEOF
}
if err != nil {
return errors.StructuralError("subkey signature invalid: " + err.Error())
}
var ok bool
subKey.Sig, ok = p.(*packet.Signature)
if !ok {
return errors.StructuralError("subkey packet not followed by signature")
}
if subKey.Sig.SigType != packet.SigTypeSubkeyBinding && subKey.Sig.SigType != packet.SigTypeSubkeyRevocation {
return errors.StructuralError("subkey signature with wrong type")
}
err = e.PrimaryKey.VerifyKeySignature(subKey.PublicKey, subKey.Sig)
if err != nil {
return errors.StructuralError("subkey signature invalid: " + err.Error())
}
e.Subkeys = append(e.Subkeys, subKey)
return nil
}
// 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
}
// parseRSA parses RSA public key material from the given Reader. See RFC 4880,
// section 5.5.2.
func (pk *PublicKeyV3) parseRSA(r io.Reader) (err error) {
if pk.n.bytes, pk.n.bitLength, err = readMPI(r); err != nil {
return
}
if pk.e.bytes, pk.e.bitLength, err = readMPI(r); err != nil {
return
}
// RFC 4880 Section 12.2 requires the low 8 bytes of the
// modulus to form the key id.
if len(pk.n.bytes) < 8 {
return errors.StructuralError("v3 public key modulus is too short")
}
if len(pk.e.bytes) > 3 {
err = errors.UnsupportedError("large public exponent")
return
}
rsa := &rsa.PublicKey{N: new(big.Int).SetBytes(pk.n.bytes)}
for i := 0; i < len(pk.e.bytes); i++ {
rsa.E <<= 8
rsa.E |= int(pk.e.bytes[i])
}
pk.PublicKey = rsa
return
}
func (scr *signatureCheckReader) Read(buf []byte) (n int, err error) {
n, err = scr.md.LiteralData.Body.Read(buf)
scr.wrappedHash.Write(buf[:n])
if err == io.EOF {
var p packet.Packet
p, scr.md.SignatureError = scr.packets.Next()
if scr.md.SignatureError != nil {
return
}
var ok bool
if scr.md.Signature, ok = p.(*packet.Signature); !ok {
scr.md.SignatureError = errors.StructuralError("LiteralData not followed by Signature")
return
}
scr.md.SignatureError = scr.md.SignedBy.PublicKey.VerifySignature(scr.h, scr.md.Signature)
// The SymmetricallyEncrypted packet, if any, might have an
// unsigned hash of its own. In order to check this we need to
// close that Reader.
if scr.md.decrypted != nil {
mdcErr := scr.md.decrypted.Close()
if mdcErr != nil {
err = mdcErr
}
}
}
return
}
// Push causes the Reader to start reading from a new io.Reader. When an EOF
// error is seen from the new io.Reader, it is popped and the Reader continues
// to read from the next most recent io.Reader. Push returns a StructuralError
// if pushing the reader would exceed the maximum recursion level, otherwise it
// returns nil.
func (r *Reader) Push(reader io.Reader) (err error) {
if len(r.readers) >= maxReaders {
return errors.StructuralError("too many layers of packets")
}
r.readers = append(r.readers, reader)
return nil
}
// Decrypt decrypts an encrypted private key using a passphrase.
func (pk *PrivateKey) Decrypt(passphrase []byte) error {
if !pk.Encrypted {
return nil
}
key := make([]byte, pk.cipher.KeySize())
pk.s2k(key, passphrase)
block := pk.cipher.new(key)
cfb := cipher.NewCFBDecrypter(block, pk.iv)
data := make([]byte, len(pk.encryptedData))
cfb.XORKeyStream(data, pk.encryptedData)
if pk.sha1Checksum {
if len(data) < sha1.Size {
return errors.StructuralError("truncated private key data")
}
h := sha1.New()
h.Write(data[:len(data)-sha1.Size])
sum := h.Sum(nil)
if !bytes.Equal(sum, data[len(data)-sha1.Size:]) {
return errors.StructuralError("private key checksum failure")
}
data = data[:len(data)-sha1.Size]
} else {
if len(data) < 2 {
return errors.StructuralError("truncated private key data")
}
var sum uint16
for i := 0; i < len(data)-2; i++ {
sum += uint16(data[i])
}
if data[len(data)-2] != uint8(sum>>8) ||
data[len(data)-1] != uint8(sum) {
return errors.StructuralError("private key checksum failure")
}
data = data[:len(data)-2]
}
return pk.parsePrivateKey(data)
}
// readHeader parses a packet header and returns an io.Reader which will return
// the contents of the packet. See RFC 4880, section 4.2.
func readHeader(r io.Reader) (tag packetType, length int64, contents io.Reader, err error) {
var buf [4]byte
_, err = io.ReadFull(r, buf[:1])
if err != nil {
return
}
if buf[0]&0x80 == 0 {
err = errors.StructuralError("tag byte does not have MSB set")
return
}
if buf[0]&0x40 == 0 {
// Old format packet
tag = packetType((buf[0] & 0x3f) >> 2)
lengthType := buf[0] & 3
if lengthType == 3 {
length = -1
contents = r
return
}
lengthBytes := 1 << lengthType
_, err = readFull(r, buf[0:lengthBytes])
if err != nil {
return
}
for i := 0; i < lengthBytes; i++ {
length <<= 8
length |= int64(buf[i])
}
contents = &spanReader{r, length}
return
}
// New format packet
tag = packetType(buf[0] & 0x3f)
length, isPartial, err := readLength(r)
if err != nil {
return
}
if isPartial {
contents = &partialLengthReader{
remaining: length,
isPartial: true,
r: r,
}
length = -1
} else {
contents = &spanReader{r, length}
}
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
}
func nextSubpacket(contents []byte) (subHeaderLen int, subPacket *OpaqueSubpacket, err error) {
// RFC 4880, section 5.2.3.1
var subLen uint32
if len(contents) < 1 {
goto Truncated
}
subPacket = &OpaqueSubpacket{}
switch {
case contents[0] < 192:
subHeaderLen = 2 // 1 length byte, 1 subtype byte
if len(contents) < subHeaderLen {
goto Truncated
}
subLen = uint32(contents[0])
contents = contents[1:]
case contents[0] < 255:
subHeaderLen = 3 // 2 length bytes, 1 subtype
if len(contents) < subHeaderLen {
goto Truncated
}
subLen = uint32(contents[0]-192)<<8 + uint32(contents[1]) + 192
contents = contents[2:]
default:
subHeaderLen = 6 // 5 length bytes, 1 subtype
if len(contents) < subHeaderLen {
goto Truncated
}
subLen = uint32(contents[1])<<24 |
uint32(contents[2])<<16 |
uint32(contents[3])<<8 |
uint32(contents[4])
contents = contents[5:]
}
if subLen > uint32(len(contents)) || subLen == 0 {
goto Truncated
}
subPacket.SubType = contents[0]
subPacket.Contents = contents[1:subLen]
return
Truncated:
err = errors.StructuralError("subpacket truncated")
return
}
// Decrypt attempts to decrypt an encrypted session key and returns the key and
// the cipher to use when decrypting a subsequent Symmetrically Encrypted Data
// packet.
func (ske *SymmetricKeyEncrypted) Decrypt(passphrase []byte) ([]byte, CipherFunction, error) {
key := make([]byte, ske.CipherFunc.KeySize())
ske.s2k(key, passphrase)
if len(ske.encryptedKey) == 0 {
return key, ske.CipherFunc, nil
}
// the IV is all zeros
iv := make([]byte, ske.CipherFunc.blockSize())
c := cipher.NewCFBDecrypter(ske.CipherFunc.new(key), iv)
plaintextKey := make([]byte, len(ske.encryptedKey))
c.XORKeyStream(plaintextKey, ske.encryptedKey)
cipherFunc := CipherFunction(plaintextKey[0])
if cipherFunc.blockSize() == 0 {
return nil, ske.CipherFunc, errors.UnsupportedError("unknown cipher: " + strconv.Itoa(int(ske.CipherFunc)))
}
plaintextKey = plaintextKey[1:]
if l := len(plaintextKey); l == 0 || l%cipherFunc.blockSize() != 0 {
return nil, cipherFunc, errors.StructuralError("length of decrypted key not a multiple of block size")
}
return plaintextKey, cipherFunc, nil
}
// ReadMessage parses an OpenPGP message that may be signed and/or encrypted.
// The given KeyRing should contain both public keys (for signature
// verification) and, possibly encrypted, private keys for decrypting.
// If config is nil, sensible defaults will be used.
func ReadMessage(r io.Reader, keyring KeyRing, prompt PromptFunction, config *packet.Config) (md *MessageDetails, err error) {
var p packet.Packet
var symKeys []*packet.SymmetricKeyEncrypted
var pubKeys []keyEnvelopePair
var se *packet.SymmetricallyEncrypted
packets := packet.NewReader(r)
md = new(MessageDetails)
md.IsEncrypted = true
// The message, if encrypted, starts with a number of packets
// containing an encrypted decryption key. The decryption key is either
// encrypted to a public key, or with a passphrase. This loop
// collects these packets.
ParsePackets:
for {
p, err = packets.Next()
if err != nil {
return nil, err
}
switch p := p.(type) {
case *packet.SymmetricKeyEncrypted:
// This packet contains the decryption key encrypted with a passphrase.
md.IsSymmetricallyEncrypted = true
symKeys = append(symKeys, p)
case *packet.EncryptedKey:
// This packet contains the decryption key encrypted to a public key.
md.EncryptedToKeyIds = append(md.EncryptedToKeyIds, p.KeyId)
switch p.Algo {
case packet.PubKeyAlgoRSA, packet.PubKeyAlgoRSAEncryptOnly, packet.PubKeyAlgoElGamal:
break
default:
continue
}
var keys []Key
if p.KeyId == 0 {
keys = keyring.DecryptionKeys()
} else {
keys = keyring.KeysById(p.KeyId)
}
for _, k := range keys {
pubKeys = append(pubKeys, keyEnvelopePair{k, p})
}
case *packet.SymmetricallyEncrypted:
se = p
break ParsePackets
case *packet.Compressed, *packet.LiteralData, *packet.OnePassSignature:
// This message isn't encrypted.
if len(symKeys) != 0 || len(pubKeys) != 0 {
return nil, errors.StructuralError("key material not followed by encrypted message")
}
packets.Unread(p)
return readSignedMessage(packets, nil, keyring)
}
}
var candidates []Key
var decrypted io.ReadCloser
// Now that we have the list of encrypted keys we need to decrypt at
// least one of them or, if we cannot, we need to call the prompt
// function so that it can decrypt a key or give us a passphrase.
FindKey:
for {
// See if any of the keys already have a private key available
candidates = candidates[:0]
candidateFingerprints := make(map[string]bool)
for _, pk := range pubKeys {
if pk.key.PrivateKey == nil {
continue
}
if !pk.key.PrivateKey.Encrypted {
if len(pk.encryptedKey.Key) == 0 {
pk.encryptedKey.Decrypt(pk.key.PrivateKey, config)
}
if len(pk.encryptedKey.Key) == 0 {
continue
}
decrypted, err = se.Decrypt(pk.encryptedKey.CipherFunc, pk.encryptedKey.Key)
if err != nil && err != errors.ErrKeyIncorrect {
return nil, err
}
if decrypted != nil {
md.DecryptedWith = pk.key
break FindKey
}
} else {
fpr := string(pk.key.PublicKey.Fingerprint[:])
if v := candidateFingerprints[fpr]; v {
continue
}
candidates = append(candidates, pk.key)
candidateFingerprints[fpr] = true
}
}
if len(candidates) == 0 && len(symKeys) == 0 {
return nil, errors.ErrKeyIncorrect
}
if prompt == nil {
return nil, errors.ErrKeyIncorrect
}
passphrase, err := prompt(candidates, len(symKeys) != 0)
if err != nil {
return nil, err
}
// Try the symmetric passphrase first
if len(symKeys) != 0 && passphrase != nil {
for _, s := range symKeys {
key, cipherFunc, err := s.Decrypt(passphrase)
if err == nil {
decrypted, err = se.Decrypt(cipherFunc, key)
if err != nil && err != errors.ErrKeyIncorrect {
return nil, err
}
if decrypted != nil {
break FindKey
}
}
}
}
}
md.decrypted = decrypted
if err := packets.Push(decrypted); err != nil {
return nil, err
}
return readSignedMessage(packets, md, keyring)
}
// CheckDetachedSignature takes a signed file and a detached signature and
// returns the signer if the signature is valid. If the signer isn't known,
// ErrUnknownIssuer is returned.
func CheckDetachedSignature(keyring KeyRing, signed, signature io.Reader) (signer *Entity, err error) {
var issuerKeyId uint64
var hashFunc crypto.Hash
var sigType packet.SignatureType
var keys []Key
var p packet.Packet
packets := packet.NewReader(signature)
for {
p, err = packets.Next()
if err == io.EOF {
return nil, errors.ErrUnknownIssuer
}
if err != nil {
return nil, err
}
switch sig := p.(type) {
case *packet.Signature:
if sig.IssuerKeyId == nil {
return nil, errors.StructuralError("signature doesn't have an issuer")
}
issuerKeyId = *sig.IssuerKeyId
hashFunc = sig.Hash
sigType = sig.SigType
case *packet.SignatureV3:
issuerKeyId = sig.IssuerKeyId
hashFunc = sig.Hash
sigType = sig.SigType
default:
return nil, errors.StructuralError("non signature packet found")
}
keys = keyring.KeysByIdUsage(issuerKeyId, packet.KeyFlagSign)
if len(keys) > 0 {
break
}
}
if len(keys) == 0 {
panic("unreachable")
}
h, wrappedHash, err := hashForSignature(hashFunc, sigType)
if err != nil {
return nil, err
}
if _, err := io.Copy(wrappedHash, signed); err != nil && err != io.EOF {
return nil, err
}
for _, key := range keys {
switch sig := p.(type) {
case *packet.Signature:
err = key.PublicKey.VerifySignature(h, sig)
case *packet.SignatureV3:
err = key.PublicKey.VerifySignatureV3(h, sig)
default:
panic("unreachable")
}
if err == nil {
return key.Entity, nil
}
}
return nil, err
}
// ReadEntity reads an entity (public key, identities, subkeys etc) from the
// given Reader.
func ReadEntity(packets *packet.Reader) (*Entity, error) {
e := new(Entity)
e.Identities = make(map[string]*Identity)
p, err := packets.Next()
if err != nil {
return nil, err
}
var ok bool
if e.PrimaryKey, ok = p.(*packet.PublicKey); !ok {
if e.PrivateKey, ok = p.(*packet.PrivateKey); !ok {
packets.Unread(p)
return nil, errors.StructuralError("first packet was not a public/private key")
} else {
e.PrimaryKey = &e.PrivateKey.PublicKey
}
}
if !e.PrimaryKey.PubKeyAlgo.CanSign() {
return nil, errors.StructuralError("primary key cannot be used for signatures")
}
var current *Identity
var revocations []*packet.Signature
EachPacket:
for {
p, err := packets.Next()
if err == io.EOF {
break
} else if err != nil {
return nil, err
}
switch pkt := p.(type) {
case *packet.UserId:
current = new(Identity)
current.Name = pkt.Id
current.UserId = pkt
e.Identities[pkt.Id] = current
for {
p, err = packets.Next()
if err == io.EOF {
return nil, io.ErrUnexpectedEOF
} else if err != nil {
return nil, err
}
sig, ok := p.(*packet.Signature)
if !ok {
return nil, errors.StructuralError("user ID packet not followed by self-signature")
}
if (sig.SigType == packet.SigTypePositiveCert || sig.SigType == packet.SigTypeGenericCert) && sig.IssuerKeyId != nil && *sig.IssuerKeyId == e.PrimaryKey.KeyId {
if err = e.PrimaryKey.VerifyUserIdSignature(pkt.Id, e.PrimaryKey, sig); err != nil {
return nil, errors.StructuralError("user ID self-signature invalid: " + err.Error())
}
current.SelfSignature = sig
break
}
current.Signatures = append(current.Signatures, sig)
}
case *packet.Signature:
if pkt.SigType == packet.SigTypeKeyRevocation {
revocations = append(revocations, pkt)
} else if pkt.SigType == packet.SigTypeDirectSignature {
// TODO: RFC4880 5.2.1 permits signatures
// directly on keys (eg. to bind additional
// revocation keys).
} else if current == nil {
return nil, errors.StructuralError("signature packet found before user id packet")
} else {
current.Signatures = append(current.Signatures, pkt)
}
case *packet.PrivateKey:
if pkt.IsSubkey == false {
packets.Unread(p)
break EachPacket
}
err = addSubkey(e, packets, &pkt.PublicKey, pkt)
if err != nil {
return nil, err
}
case *packet.PublicKey:
if pkt.IsSubkey == false {
packets.Unread(p)
break EachPacket
}
err = addSubkey(e, packets, pkt, nil)
if err != nil {
return nil, err
}
default:
// we ignore unknown packets
}
}
if len(e.Identities) == 0 {
return nil, errors.StructuralError("entity without any identities")
}
for _, revocation := range revocations {
err = e.PrimaryKey.VerifyRevocationSignature(revocation)
if err == nil {
e.Revocations = append(e.Revocations, revocation)
} else {
// TODO: RFC 4880 5.2.3.15 defines revocation keys.
return nil, errors.StructuralError("revocation signature signed by alternate key")
}
}
return e, nil
}
// base64-encoded Bytes
// '=' base64 encoded checksum
// -----END Type-----
// where Headers is a possibly empty sequence of Key: Value lines.
//
// Since the armored data can be very large, this package presents a streaming
// interface.
type Block struct {
Type string // The type, taken from the preamble (i.e. "PGP SIGNATURE").
Header map[string]string // Optional headers.
Body io.Reader // A Reader from which the contents can be read
lReader lineReader
oReader openpgpReader
}
var ArmorCorrupt error = errors.StructuralError("armor invalid")
const crc24Init = 0xb704ce
const crc24Poly = 0x1864cfb
const crc24Mask = 0xffffff
// crc24 calculates the OpenPGP checksum as specified in RFC 4880, section 6.1
func crc24(crc uint32, d []byte) uint32 {
for _, b := range d {
crc ^= uint32(b) << 16
for i := 0; i < 8; i++ {
crc <<= 1
if crc&0x1000000 != 0 {
crc ^= crc24Poly
}
}
// 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:
// 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. In practice, the subpacket is used exclusively to
// indicate support for MDC-protected encryption.
sig.MDC = len(subpacket) >= 1 && subpacket[0]&1 == 1
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)))
}
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
}