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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"
"errors"
"io"
"golang.org/x/crypto/openpgp/armor"
"golang.org/x/crypto/openpgp/packet"
)
const maxLiteralSize = (1 << 31) - 512 // int32_max minus some room for the literal data header
// MergeSignature combines a detached signature with a cleartext message and writes it as an inline signed message with optional ASCII armor
func MergeSignature(w io.Writer, sig []byte, message io.Reader, withArmor bool, filename string) (err error) {
var armorer io.WriteCloser = nopCloseWriter{w}
if withArmor {
armorer, err = armor.Encode(w, "PGP MESSAGE", nil)
if err != nil {
return err
}
}
// write one-pass signature header
if err := writeOnePass(armorer, sig); err != nil {
return err
}
// write literal data
if size := getSize(message); size >= 0 {
if err := serializeLiteral(armorer, message, size, filename); err != nil {
return err
}
} else {
litWriter, err := packet.SerializeLiteral(nopCloseWriter{armorer}, true, filename, 0)
if err != nil {
return err
}
if _, err := io.Copy(litWriter, message); err != nil {
return err
}
if err := litWriter.Close(); err != nil {
return err
}
}
// write signature
if _, err := armorer.Write(sig); err != nil {
return err
}
return armorer.Close()
}
// write a one-pass signature header with the fields copied from the detached signature in sig
func writeOnePass(w io.Writer, sig []byte) error {
genpkt, err := packet.Read(bytes.NewReader(sig))
if err != nil {
return err
}
// parse
op := packet.OnePassSignature{IsLast: true}
switch pkt := genpkt.(type) {
case *packet.SignatureV3:
op.SigType = pkt.SigType
op.Hash = pkt.Hash
op.PubKeyAlgo = pkt.PubKeyAlgo
op.KeyId = pkt.IssuerKeyId
case *packet.Signature:
op.SigType = pkt.SigType
op.Hash = pkt.Hash
op.PubKeyAlgo = pkt.PubKeyAlgo
if pkt.IssuerKeyId != nil {
op.KeyId = *pkt.IssuerKeyId
}
default:
return errors.New("not a PGP signature")
}
return op.Serialize(w)
}
// write size bytes from r into w as a literal data packet
func serializeLiteral(w io.Writer, r io.Reader, size int32, filename string) error {
if len(filename) > 255 {
filename = filename[:255]
}
var buf bytes.Buffer
buf.WriteByte('b') // binary mode
buf.WriteByte(byte(len(filename))) // filename
buf.WriteString(filename) // filename
buf.Write([]byte{0, 0, 0, 0}) // timestamp
packetType := 11 // literal data
psize := int64(size) + int64(buf.Len())
if psize > (2<<31)-1 {
return errors.New("literal too big")
}
if err := serializeHeader(w, packetType, int(psize)); err != nil {
return err
}
if _, err := w.Write(buf.Bytes()); err != nil {
return err
}
_, err := io.CopyN(w, r, int64(size))
return err
}
// get the size from a reader if it's seekable and not too big to fit in a single literal data packet, otherwise returns -1
func getSize(r io.Reader) int32 {
seek, ok := r.(io.Seeker)
if !ok {
return -1
}
start, err := seek.Seek(0, io.SeekCurrent)
if err != nil {
return -1
}
end, err := seek.Seek(0, io.SeekEnd)
if err != nil {
return -1
}
_, err = seek.Seek(start, io.SeekStart)
if err != nil {
return -1
}
size := end - start
if size > maxLiteralSize {
return -1
}
return int32(size)
}
// serializeHeader writes an OpenPGP packet header to w. See RFC 4880, section
// 4.2.
func serializeHeader(w io.Writer, ptype int, length int) (err error) {
var buf [6]byte
var n int
buf[0] = 0x80 | 0x40 | byte(ptype)
if length < 192 {
buf[1] = byte(length)
n = 2
} else if length < 8384 {
length -= 192
buf[1] = 192 + byte(length>>8)
buf[2] = byte(length)
n = 3
} else {
buf[1] = 255
buf[2] = byte(length >> 24)
buf[3] = byte(length >> 16)
buf[4] = byte(length >> 8)
buf[5] = byte(length)
n = 6
}
_, err = w.Write(buf[:n])
return
}
type nopCloseWriter struct {
io.Writer
}
func (nopCloseWriter) Close() error {
return nil
}
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