// 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FlagSign, FlagEncryptCommunications, FlagEncryptStorage bool // RevocationReason is set if this signature has been revoked.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 *ReasonForRevocation 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(ReasonForRevocation) *sig.RevocationReason = ReasonForRevocation(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) } // RevokeSubkey computes a subkey 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) RevokeSubkey(pub *PublicKey, priv *PrivateKey, config *Config) error { // Identical to a subkey binding signature return sig.SignKey(pub, 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, sig.Version == 5, 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{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() }