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443 lines
13 KiB
Go
443 lines
13 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package openpgp implements high level operations on OpenPGP messages.
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package openpgp // import "golang.org/x/crypto/openpgp"
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import (
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"crypto"
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_ "crypto/sha256"
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"hash"
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"io"
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"strconv"
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"golang.org/x/crypto/openpgp/armor"
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"golang.org/x/crypto/openpgp/errors"
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"golang.org/x/crypto/openpgp/packet"
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)
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// SignatureType is the armor type for a PGP signature.
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var SignatureType = "PGP SIGNATURE"
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// readArmored reads an armored block with the given type.
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func readArmored(r io.Reader, expectedType string) (body io.Reader, err error) {
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block, err := armor.Decode(r)
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if err != nil {
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return
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}
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if block.Type != expectedType {
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return nil, errors.InvalidArgumentError("expected '" + expectedType + "', got: " + block.Type)
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}
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return block.Body, nil
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}
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// MessageDetails contains the result of parsing an OpenPGP encrypted and/or
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// signed message.
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type MessageDetails struct {
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IsEncrypted bool // true if the message was encrypted.
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EncryptedToKeyIds []uint64 // the list of recipient key ids.
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IsSymmetricallyEncrypted bool // true if a passphrase could have decrypted the message.
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DecryptedWith Key // the private key used to decrypt the message, if any.
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IsSigned bool // true if the message is signed.
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SignedByKeyId uint64 // the key id of the signer, if any.
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SignedBy *Key // the key of the signer, if available.
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LiteralData *packet.LiteralData // the metadata of the contents
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UnverifiedBody io.Reader // the contents of the message.
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// If IsSigned is true and SignedBy is non-zero then the signature will
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// be verified as UnverifiedBody is read. The signature cannot be
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// checked until the whole of UnverifiedBody is read so UnverifiedBody
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// must be consumed until EOF before the data can be trusted. Even if a
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// message isn't signed (or the signer is unknown) the data may contain
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// an authentication code that is only checked once UnverifiedBody has
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// been consumed. Once EOF has been seen, the following fields are
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// valid. (An authentication code failure is reported as a
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// SignatureError error when reading from UnverifiedBody.)
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SignatureError error // nil if the signature is good.
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Signature *packet.Signature // the signature packet itself, if v4 (default)
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SignatureV3 *packet.SignatureV3 // the signature packet if it is a v2 or v3 signature
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decrypted io.ReadCloser
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}
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// A PromptFunction is used as a callback by functions that may need to decrypt
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// a private key, or prompt for a passphrase. It is called with a list of
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// acceptable, encrypted private keys and a boolean that indicates whether a
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// passphrase is usable. It should either decrypt a private key or return a
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// passphrase to try. If the decrypted private key or given passphrase isn't
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// correct, the function will be called again, forever. Any error returned will
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// be passed up.
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type PromptFunction func(keys []Key, symmetric bool) ([]byte, error)
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// A keyEnvelopePair is used to store a private key with the envelope that
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// contains a symmetric key, encrypted with that key.
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type keyEnvelopePair struct {
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key Key
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encryptedKey *packet.EncryptedKey
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}
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// ReadMessage parses an OpenPGP message that may be signed and/or encrypted.
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// The given KeyRing should contain both public keys (for signature
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// verification) and, possibly encrypted, private keys for decrypting.
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// If config is nil, sensible defaults will be used.
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func ReadMessage(r io.Reader, keyring KeyRing, prompt PromptFunction, config *packet.Config) (md *MessageDetails, err error) {
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var p packet.Packet
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var symKeys []*packet.SymmetricKeyEncrypted
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var pubKeys []keyEnvelopePair
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var se *packet.SymmetricallyEncrypted
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packets := packet.NewReader(r)
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md = new(MessageDetails)
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md.IsEncrypted = true
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// The message, if encrypted, starts with a number of packets
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// containing an encrypted decryption key. The decryption key is either
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// encrypted to a public key, or with a passphrase. This loop
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// collects these packets.
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ParsePackets:
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for {
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p, err = packets.Next()
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if err != nil {
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return nil, err
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}
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switch p := p.(type) {
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case *packet.SymmetricKeyEncrypted:
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// This packet contains the decryption key encrypted with a passphrase.
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md.IsSymmetricallyEncrypted = true
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symKeys = append(symKeys, p)
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case *packet.EncryptedKey:
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// This packet contains the decryption key encrypted to a public key.
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md.EncryptedToKeyIds = append(md.EncryptedToKeyIds, p.KeyId)
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switch p.Algo {
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case packet.PubKeyAlgoRSA, packet.PubKeyAlgoRSAEncryptOnly, packet.PubKeyAlgoElGamal:
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break
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default:
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continue
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}
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var keys []Key
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if p.KeyId == 0 {
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keys = keyring.DecryptionKeys()
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} else {
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keys = keyring.KeysById(p.KeyId)
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}
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for _, k := range keys {
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pubKeys = append(pubKeys, keyEnvelopePair{k, p})
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}
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case *packet.SymmetricallyEncrypted:
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se = p
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break ParsePackets
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case *packet.Compressed, *packet.LiteralData, *packet.OnePassSignature:
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// This message isn't encrypted.
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if len(symKeys) != 0 || len(pubKeys) != 0 {
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return nil, errors.StructuralError("key material not followed by encrypted message")
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}
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packets.Unread(p)
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return readSignedMessage(packets, nil, keyring)
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}
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}
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var candidates []Key
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var decrypted io.ReadCloser
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// Now that we have the list of encrypted keys we need to decrypt at
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// least one of them or, if we cannot, we need to call the prompt
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// function so that it can decrypt a key or give us a passphrase.
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FindKey:
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for {
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// See if any of the keys already have a private key available
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candidates = candidates[:0]
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candidateFingerprints := make(map[string]bool)
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for _, pk := range pubKeys {
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if pk.key.PrivateKey == nil {
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continue
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}
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if !pk.key.PrivateKey.Encrypted {
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if len(pk.encryptedKey.Key) == 0 {
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pk.encryptedKey.Decrypt(pk.key.PrivateKey, config)
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}
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if len(pk.encryptedKey.Key) == 0 {
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continue
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}
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decrypted, err = se.Decrypt(pk.encryptedKey.CipherFunc, pk.encryptedKey.Key)
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if err != nil && err != errors.ErrKeyIncorrect {
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return nil, err
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}
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if decrypted != nil {
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md.DecryptedWith = pk.key
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break FindKey
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}
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} else {
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fpr := string(pk.key.PublicKey.Fingerprint[:])
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if v := candidateFingerprints[fpr]; v {
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continue
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}
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candidates = append(candidates, pk.key)
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candidateFingerprints[fpr] = true
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}
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}
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if len(candidates) == 0 && len(symKeys) == 0 {
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return nil, errors.ErrKeyIncorrect
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}
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if prompt == nil {
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return nil, errors.ErrKeyIncorrect
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}
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passphrase, err := prompt(candidates, len(symKeys) != 0)
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if err != nil {
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return nil, err
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}
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// Try the symmetric passphrase first
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if len(symKeys) != 0 && passphrase != nil {
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for _, s := range symKeys {
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key, cipherFunc, err := s.Decrypt(passphrase)
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if err == nil {
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decrypted, err = se.Decrypt(cipherFunc, key)
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if err != nil && err != errors.ErrKeyIncorrect {
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return nil, err
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}
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if decrypted != nil {
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break FindKey
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}
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}
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}
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}
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}
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md.decrypted = decrypted
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if err := packets.Push(decrypted); err != nil {
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return nil, err
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}
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return readSignedMessage(packets, md, keyring)
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}
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// readSignedMessage reads a possibly signed message if mdin is non-zero then
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// that structure is updated and returned. Otherwise a fresh MessageDetails is
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// used.
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func readSignedMessage(packets *packet.Reader, mdin *MessageDetails, keyring KeyRing) (md *MessageDetails, err error) {
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if mdin == nil {
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mdin = new(MessageDetails)
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}
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md = mdin
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var p packet.Packet
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var h hash.Hash
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var wrappedHash hash.Hash
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FindLiteralData:
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for {
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p, err = packets.Next()
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if err != nil {
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return nil, err
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}
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switch p := p.(type) {
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case *packet.Compressed:
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if err := packets.Push(p.Body); err != nil {
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return nil, err
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}
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case *packet.OnePassSignature:
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if !p.IsLast {
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return nil, errors.UnsupportedError("nested signatures")
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}
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h, wrappedHash, err = hashForSignature(p.Hash, p.SigType)
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if err != nil {
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md = nil
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return
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}
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md.IsSigned = true
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md.SignedByKeyId = p.KeyId
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keys := keyring.KeysByIdUsage(p.KeyId, packet.KeyFlagSign)
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if len(keys) > 0 {
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md.SignedBy = &keys[0]
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}
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case *packet.LiteralData:
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md.LiteralData = p
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break FindLiteralData
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}
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}
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if md.SignedBy != nil {
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md.UnverifiedBody = &signatureCheckReader{packets, h, wrappedHash, md}
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} else if md.decrypted != nil {
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md.UnverifiedBody = checkReader{md}
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} else {
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md.UnverifiedBody = md.LiteralData.Body
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}
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return md, nil
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}
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// hashForSignature returns a pair of hashes that can be used to verify a
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// signature. The signature may specify that the contents of the signed message
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// should be preprocessed (i.e. to normalize line endings). Thus this function
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// returns two hashes. The second should be used to hash the message itself and
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// performs any needed preprocessing.
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func hashForSignature(hashId crypto.Hash, sigType packet.SignatureType) (hash.Hash, hash.Hash, error) {
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if !hashId.Available() {
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return nil, nil, errors.UnsupportedError("hash not available: " + strconv.Itoa(int(hashId)))
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}
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h := hashId.New()
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switch sigType {
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case packet.SigTypeBinary:
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return h, h, nil
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case packet.SigTypeText:
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return h, NewCanonicalTextHash(h), nil
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}
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return nil, nil, errors.UnsupportedError("unsupported signature type: " + strconv.Itoa(int(sigType)))
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}
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// checkReader wraps an io.Reader from a LiteralData packet. When it sees EOF
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// it closes the ReadCloser from any SymmetricallyEncrypted packet to trigger
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// MDC checks.
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type checkReader struct {
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md *MessageDetails
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}
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func (cr checkReader) Read(buf []byte) (n int, err error) {
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n, err = cr.md.LiteralData.Body.Read(buf)
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if err == io.EOF {
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mdcErr := cr.md.decrypted.Close()
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if mdcErr != nil {
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err = mdcErr
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}
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}
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return
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}
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// signatureCheckReader wraps an io.Reader from a LiteralData packet and hashes
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// the data as it is read. When it sees an EOF from the underlying io.Reader
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// it parses and checks a trailing Signature packet and triggers any MDC checks.
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type signatureCheckReader struct {
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packets *packet.Reader
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h, wrappedHash hash.Hash
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md *MessageDetails
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}
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func (scr *signatureCheckReader) Read(buf []byte) (n int, err error) {
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n, err = scr.md.LiteralData.Body.Read(buf)
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scr.wrappedHash.Write(buf[:n])
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if err == io.EOF {
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var p packet.Packet
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p, scr.md.SignatureError = scr.packets.Next()
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if scr.md.SignatureError != nil {
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return
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}
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var ok bool
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if scr.md.Signature, ok = p.(*packet.Signature); ok {
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scr.md.SignatureError = scr.md.SignedBy.PublicKey.VerifySignature(scr.h, scr.md.Signature)
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} else if scr.md.SignatureV3, ok = p.(*packet.SignatureV3); ok {
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scr.md.SignatureError = scr.md.SignedBy.PublicKey.VerifySignatureV3(scr.h, scr.md.SignatureV3)
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} else {
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scr.md.SignatureError = errors.StructuralError("LiteralData not followed by Signature")
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return
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}
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// The SymmetricallyEncrypted packet, if any, might have an
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// unsigned hash of its own. In order to check this we need to
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// close that Reader.
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if scr.md.decrypted != nil {
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mdcErr := scr.md.decrypted.Close()
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if mdcErr != nil {
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err = mdcErr
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}
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}
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}
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return
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}
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// CheckDetachedSignature takes a signed file and a detached signature and
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// returns the signer if the signature is valid. If the signer isn't known,
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// ErrUnknownIssuer is returned.
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func CheckDetachedSignature(keyring KeyRing, signed, signature io.Reader) (signer *Entity, err error) {
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var issuerKeyId uint64
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var hashFunc crypto.Hash
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var sigType packet.SignatureType
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var keys []Key
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var p packet.Packet
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packets := packet.NewReader(signature)
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for {
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p, err = packets.Next()
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if err == io.EOF {
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return nil, errors.ErrUnknownIssuer
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}
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if err != nil {
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return nil, err
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}
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switch sig := p.(type) {
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case *packet.Signature:
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if sig.IssuerKeyId == nil {
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return nil, errors.StructuralError("signature doesn't have an issuer")
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}
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issuerKeyId = *sig.IssuerKeyId
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hashFunc = sig.Hash
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sigType = sig.SigType
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case *packet.SignatureV3:
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issuerKeyId = sig.IssuerKeyId
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hashFunc = sig.Hash
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sigType = sig.SigType
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default:
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return nil, errors.StructuralError("non signature packet found")
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}
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keys = keyring.KeysByIdUsage(issuerKeyId, packet.KeyFlagSign)
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if len(keys) > 0 {
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break
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}
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}
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if len(keys) == 0 {
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panic("unreachable")
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}
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h, wrappedHash, err := hashForSignature(hashFunc, sigType)
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if err != nil {
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return nil, err
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}
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if _, err := io.Copy(wrappedHash, signed); err != nil && err != io.EOF {
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return nil, err
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}
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for _, key := range keys {
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switch sig := p.(type) {
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case *packet.Signature:
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err = key.PublicKey.VerifySignature(h, sig)
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case *packet.SignatureV3:
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err = key.PublicKey.VerifySignatureV3(h, sig)
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default:
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panic("unreachable")
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}
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if err == nil {
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return key.Entity, nil
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}
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}
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return nil, err
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}
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// CheckArmoredDetachedSignature performs the same actions as
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// CheckDetachedSignature but expects the signature to be armored.
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func CheckArmoredDetachedSignature(keyring KeyRing, signed, signature io.Reader) (signer *Entity, err error) {
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body, err := readArmored(signature, SignatureType)
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if err != nil {
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return
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}
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return CheckDetachedSignature(keyring, signed, body)
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}
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