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//
// Copyright (c) SAS Institute Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
package pgptools
import (
"bytes"
"crypto"
"errors"
"fmt"
"io"
"io/ioutil"
"time"
"golang.org/x/crypto/openpgp"
"golang.org/x/crypto/openpgp/clearsign"
"golang.org/x/crypto/openpgp/packet"
)
type PgpSignature struct {
Key *openpgp.Key
CreationTime time.Time
Hash crypto.Hash
}
// Verify a detached PGP signature in "signature" over the document in
// "signed", using keys from "keyring". Returns a value of ErrNoKey if the key
// cannot be found.
func VerifyDetached(signature, signed io.Reader, keyring openpgp.EntityList) (*PgpSignature, error) {
packetReader := packet.NewReader(signature)
genpkt, err := packetReader.Next()
if err == io.EOF {
return nil, errors.New("no PGP signature found")
} else if err != nil {
return nil, err
}
// parse
var hash crypto.Hash
var keyID uint64
var creationTime time.Time
switch pkt := genpkt.(type) {
case *packet.SignatureV3:
hash = pkt.Hash
keyID = pkt.IssuerKeyId
creationTime = pkt.CreationTime
case *packet.Signature:
if pkt.IssuerKeyId == nil {
return nil, errors.New("Missing keyId in signature")
}
hash = pkt.Hash
keyID = *pkt.IssuerKeyId
creationTime = pkt.CreationTime
default:
return nil, errors.New("not a PGP signature")
}
// find key
keys := keyring.KeysById(keyID)
if len(keys) == 0 {
return nil, ErrNoKey(keyID)
}
// calculate hash
if !hash.Available() {
return nil, errors.New("signature uses unknown digest")
}
d := hash.New()
if _, err := io.Copy(d, signed); err != nil {
return nil, err
}
// check signature
switch pkt := genpkt.(type) {
case *packet.SignatureV3:
err = keys[0].PublicKey.VerifySignatureV3(d, pkt)
case *packet.Signature:
err = keys[0].PublicKey.VerifySignature(d, pkt)
}
return &PgpSignature{&keys[0], creationTime, hash}, err
}
// Verify a cleartext PGP signature in "signature" using keys from "keyring".
// Returns a value of ErrNoKey in the key cannot be found. If "cleartext" is
// not nil, then write the embedded cleartext as it is verified.
func VerifyClearSign(signature io.Reader, cleartext io.Writer, keyring openpgp.EntityList) (*PgpSignature, error) {
blob, err := ioutil.ReadAll(signature)
if err != nil {
return nil, err
}
csblock, rest := clearsign.Decode(blob)
if csblock == nil {
return nil, errors.New("malformed clearsign signature")
} else if bytes.Contains(rest, []byte("-----BEGIN")) {
return nil, errors.New("clearsign contains multiple documents")
}
if cleartext != nil {
if _, err := cleartext.Write(csblock.Bytes); err != nil {
return nil, err
}
}
sig, err := VerifyDetached(csblock.ArmoredSignature.Body, bytes.NewReader(csblock.Bytes), keyring)
return sig, err
}
// Verify an inline PGP signature in "signature" using keys from "keyring".
// Returns a value of ErrNoKey if the key cannot be found. If "cleartext" is
// not nil, then write the embedded cleartext as it is verified.
func VerifyInline(signature io.Reader, cleartext io.Writer, keyring openpgp.EntityList) (*PgpSignature, error) {
md, err := openpgp.ReadMessage(signature, keyring, nil, nil)
if err == io.EOF {
return nil, ErrNoContent{}
} else if err != nil {
return nil, err
} else if md.SignedBy == nil {
return nil, ErrNoKey(md.SignedByKeyId)
}
if cleartext == nil {
cleartext = ioutil.Discard
}
if _, err := io.Copy(cleartext, md.UnverifiedBody); err != nil {
return nil, err
}
// reading UnverifiedBody in full triggers the signature validation
sig := &PgpSignature{Key: md.SignedBy}
if md.Signature != nil {
sig.CreationTime = md.Signature.CreationTime
sig.Hash = md.Signature.Hash
} else if md.SignatureV3 != nil {
sig.CreationTime = md.SignatureV3.CreationTime
sig.Hash = md.Signature.Hash
}
return sig, md.SignatureError
}
// Returned by Verify* functions when the key used for signing is not in the
// keyring. The value is the KeyID of the missing key.
type ErrNoKey uint64
func (e ErrNoKey) Error() string {
return fmt.Sprintf("keyId %x not found", uint64(e))
}
// Returned by VerifyInline if the signature is actually a detached signature
type ErrNoContent struct{}
func (ErrNoContent) Error() string {
return "missing content for detached signature"
}
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