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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 (
"bufio"
"bytes"
"crypto"
"errors"
"io"
"io/ioutil"
"golang.org/x/crypto/openpgp"
"golang.org/x/crypto/openpgp/armor"
"golang.org/x/crypto/openpgp/clearsign"
"golang.org/x/crypto/openpgp/packet"
)
var sigHeader = []byte("-----BEGIN PGP SIGNATURE-----")
var crlf = []byte("\r\n")
// Do a cleartext signature, signing the document in "message" and writing the result to "w"
func ClearSign(w io.Writer, signer *openpgp.Entity, message io.Reader, config *packet.Config) error {
e, err := clearsign.Encode(w, signer.PrivateKey, config)
if err != nil {
return err
}
if _, err := io.Copy(e, message); err != nil {
return err
}
if err := e.Close(); err != nil {
return err
}
_, err = w.Write(crlf)
return err
}
// Do a cleartext signature but skip writing the embedded original document and
// write just the signature block to "w"
func DetachClearSign(w io.Writer, signer *openpgp.Entity, message io.Reader, config *packet.Config) error {
readPipe, writePipe := io.Pipe()
done := make(chan error)
go func() {
tail, err := tailClearSign(readPipe)
if err == nil {
_, err = w.Write(tail)
}
done <- err
}()
err := ClearSign(writePipe, signer, message, config)
_ = writePipe.CloseWithError(err)
return <-done
}
// Consume bytes from a Reader, returning only the signature block at the end
func tailClearSign(r io.Reader) ([]byte, error) {
s := bufio.NewScanner(r)
out := bytes.NewBuffer(make([]byte, 0, 1024))
copying := false
for s.Scan() {
line := s.Bytes()
if copying || bytes.Equal(line, sigHeader) {
copying = true
out.Write(line)
out.WriteString("\r\n")
}
}
return out.Bytes(), s.Err()
}
// Create a cleartext signature by merging an original document stream in
// "message" with a detached signature in "sig" produced by DetachClearSign()
func MergeClearSign(w io.Writer, sig []byte, message io.Reader) error {
config, err := configFromSig(sig)
if err != nil {
return err
}
// Make a fake entity just to get ClearSign() to produce the right framework
signer := &openpgp.Entity{PrivateKey: &packet.PrivateKey{
PrivateKey: fakeSigner{},
PublicKey: packet.PublicKey{PubKeyAlgo: packet.PubKeyAlgoRSA},
}}
out := bufio.NewWriter(w)
defer out.Flush()
readPipe, writePipe := io.Pipe()
done := make(chan error)
go func() {
done <- headClearSign(readPipe, out)
}()
err = ClearSign(writePipe, signer, message, config)
_ = writePipe.CloseWithError(err)
if err := <-done; err != nil {
return err
}
_, err = out.Write(sig)
return err
}
// Copy bytes, stopping before the signature block at the end
func headClearSign(r io.Reader, w io.Writer) error {
s := bufio.NewScanner(r)
for s.Scan() {
line := s.Bytes()
if bytes.Equal(line, sigHeader) {
// found the end of the document, drain the rest of the reader
_, err := io.Copy(ioutil.Discard, r)
return err
}
if _, err := w.Write(line); err != nil {
return err
}
if _, err := w.Write(crlf); err != nil {
return err
}
}
if s.Err() != nil {
return s.Err()
}
return errors.New("Signature block not found")
}
// Set up a pgp signature config based on the hash algorithm in an existing
// signature
func configFromSig(sigarmor []byte) (*packet.Config, error) {
block, err := armor.Decode(bytes.NewReader(sigarmor))
if err != nil {
return nil, err
}
if block.Type != "PGP SIGNATURE" {
return nil, errors.New("Not a PGP signature")
}
parser := packet.NewReader(block.Body)
pkt, err := parser.Next()
if err != nil {
return nil, errors.New("Not a PGP signature")
}
var hashFunc crypto.Hash
switch sig := pkt.(type) {
case *packet.Signature:
hashFunc = sig.Hash
case *packet.SignatureV3:
hashFunc = sig.Hash
default:
return nil, errors.New("Not a PGP signature")
}
return &packet.Config{DefaultHash: hashFunc}, nil
}
type fakeSigner struct{}
func (fakeSigner) Public() crypto.PublicKey {
return nil
}
func (fakeSigner) Sign(rand io.Reader, digest []byte, opts crypto.SignerOpts) ([]byte, error) {
return []byte("fake signature here"), nil
}
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