--- /dev/null
+// 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 openpgp implements high level operations on OpenPGP messages.
+package openpgp // import "golang.org/x/crypto/openpgp"
+
+import (
+ "crypto"
+ _ "crypto/sha256"
+ "hash"
+ "io"
+ "strconv"
+
+ "golang.org/x/crypto/openpgp/armor"
+ "golang.org/x/crypto/openpgp/errors"
+ "golang.org/x/crypto/openpgp/packet"
+)
+
+// SignatureType is the armor type for a PGP signature.
+var SignatureType = "PGP SIGNATURE"
+
+// readArmored reads an armored block with the given type.
+func readArmored(r io.Reader, expectedType string) (body io.Reader, err error) {
+ block, err := armor.Decode(r)
+ if err != nil {
+ return
+ }
+
+ if block.Type != expectedType {
+ return nil, errors.InvalidArgumentError("expected '" + expectedType + "', got: " + block.Type)
+ }
+
+ return block.Body, nil
+}
+
+// MessageDetails contains the result of parsing an OpenPGP encrypted and/or
+// signed message.
+type MessageDetails struct {
+ IsEncrypted bool // true if the message was encrypted.
+ EncryptedToKeyIds []uint64 // the list of recipient key ids.
+ IsSymmetricallyEncrypted bool // true if a passphrase could have decrypted the message.
+ DecryptedWith Key // the private key used to decrypt the message, if any.
+ IsSigned bool // true if the message is signed.
+ SignedByKeyId uint64 // the key id of the signer, if any.
+ SignedBy *Key // the key of the signer, if available.
+ LiteralData *packet.LiteralData // the metadata of the contents
+ UnverifiedBody io.Reader // the contents of the message.
+
+ // If IsSigned is true and SignedBy is non-zero then the signature will
+ // be verified as UnverifiedBody is read. The signature cannot be
+ // checked until the whole of UnverifiedBody is read so UnverifiedBody
+ // must be consumed until EOF before the data can be trusted. Even if a
+ // message isn't signed (or the signer is unknown) the data may contain
+ // an authentication code that is only checked once UnverifiedBody has
+ // been consumed. Once EOF has been seen, the following fields are
+ // valid. (An authentication code failure is reported as a
+ // SignatureError error when reading from UnverifiedBody.)
+ SignatureError error // nil if the signature is good.
+ Signature *packet.Signature // the signature packet itself, if v4 (default)
+ SignatureV3 *packet.SignatureV3 // the signature packet if it is a v2 or v3 signature
+
+ decrypted io.ReadCloser
+}
+
+// A PromptFunction is used as a callback by functions that may need to decrypt
+// a private key, or prompt for a passphrase. It is called with a list of
+// acceptable, encrypted private keys and a boolean that indicates whether a
+// passphrase is usable. It should either decrypt a private key or return a
+// passphrase to try. If the decrypted private key or given passphrase isn't
+// correct, the function will be called again, forever. Any error returned will
+// be passed up.
+type PromptFunction func(keys []Key, symmetric bool) ([]byte, error)
+
+// A keyEnvelopePair is used to store a private key with the envelope that
+// contains a symmetric key, encrypted with that key.
+type keyEnvelopePair struct {
+ key Key
+ encryptedKey *packet.EncryptedKey
+}
+
+// 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)
+}
+
+// readSignedMessage reads a possibly signed message if mdin is non-zero then
+// that structure is updated and returned. Otherwise a fresh MessageDetails is
+// used.
+func readSignedMessage(packets *packet.Reader, mdin *MessageDetails, keyring KeyRing) (md *MessageDetails, err error) {
+ if mdin == nil {
+ mdin = new(MessageDetails)
+ }
+ md = mdin
+
+ var p packet.Packet
+ var h hash.Hash
+ var wrappedHash hash.Hash
+FindLiteralData:
+ for {
+ p, err = packets.Next()
+ if err != nil {
+ return nil, err
+ }
+ switch p := p.(type) {
+ case *packet.Compressed:
+ if err := packets.Push(p.Body); err != nil {
+ return nil, err
+ }
+ case *packet.OnePassSignature:
+ if !p.IsLast {
+ return nil, errors.UnsupportedError("nested signatures")
+ }
+
+ h, wrappedHash, err = hashForSignature(p.Hash, p.SigType)
+ if err != nil {
+ md = nil
+ return
+ }
+
+ md.IsSigned = true
+ md.SignedByKeyId = p.KeyId
+ keys := keyring.KeysByIdUsage(p.KeyId, packet.KeyFlagSign)
+ if len(keys) > 0 {
+ md.SignedBy = &keys[0]
+ }
+ case *packet.LiteralData:
+ md.LiteralData = p
+ break FindLiteralData
+ }
+ }
+
+ if md.SignedBy != nil {
+ md.UnverifiedBody = &signatureCheckReader{packets, h, wrappedHash, md}
+ } else if md.decrypted != nil {
+ md.UnverifiedBody = checkReader{md}
+ } else {
+ md.UnverifiedBody = md.LiteralData.Body
+ }
+
+ return md, nil
+}
+
+// hashForSignature returns a pair of hashes that can be used to verify a
+// signature. The signature may specify that the contents of the signed message
+// should be preprocessed (i.e. to normalize line endings). Thus this function
+// returns two hashes. The second should be used to hash the message itself and
+// performs any needed preprocessing.
+func hashForSignature(hashId crypto.Hash, sigType packet.SignatureType) (hash.Hash, hash.Hash, error) {
+ if !hashId.Available() {
+ return nil, nil, errors.UnsupportedError("hash not available: " + strconv.Itoa(int(hashId)))
+ }
+ h := hashId.New()
+
+ switch sigType {
+ case packet.SigTypeBinary:
+ return h, h, nil
+ case packet.SigTypeText:
+ return h, NewCanonicalTextHash(h), nil
+ }
+
+ return nil, nil, errors.UnsupportedError("unsupported signature type: " + strconv.Itoa(int(sigType)))
+}
+
+// checkReader wraps an io.Reader from a LiteralData packet. When it sees EOF
+// it closes the ReadCloser from any SymmetricallyEncrypted packet to trigger
+// MDC checks.
+type checkReader struct {
+ md *MessageDetails
+}
+
+func (cr checkReader) Read(buf []byte) (n int, err error) {
+ n, err = cr.md.LiteralData.Body.Read(buf)
+ if err == io.EOF {
+ mdcErr := cr.md.decrypted.Close()
+ if mdcErr != nil {
+ err = mdcErr
+ }
+ }
+ return
+}
+
+// signatureCheckReader wraps an io.Reader from a LiteralData packet and hashes
+// the data as it is read. When it sees an EOF from the underlying io.Reader
+// it parses and checks a trailing Signature packet and triggers any MDC checks.
+type signatureCheckReader struct {
+ packets *packet.Reader
+ h, wrappedHash hash.Hash
+ md *MessageDetails
+}
+
+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 = scr.md.SignedBy.PublicKey.VerifySignature(scr.h, scr.md.Signature)
+ } else if scr.md.SignatureV3, ok = p.(*packet.SignatureV3); ok {
+ scr.md.SignatureError = scr.md.SignedBy.PublicKey.VerifySignatureV3(scr.h, scr.md.SignatureV3)
+ } else {
+ scr.md.SignatureError = errors.StructuralError("LiteralData not followed by Signature")
+ return
+ }
+
+ // 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
+}
+
+// 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
+}
+
+// CheckArmoredDetachedSignature performs the same actions as
+// CheckDetachedSignature but expects the signature to be armored.
+func CheckArmoredDetachedSignature(keyring KeyRing, signed, signature io.Reader) (signer *Entity, err error) {
+ body, err := readArmored(signature, SignatureType)
+ if err != nil {
+ return
+ }
+
+ return CheckDetachedSignature(keyring, signed, body)
+}
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