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// Copyright 2012 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 clearsign generates and processes OpenPGP, clear-signed data. See
// RFC 4880, section 7.
//
// Clearsigned messages are cryptographically signed, but the contents of the
// message are kept in plaintext so that it can be read without special tools.
package clearsign // import "golang.org/x/crypto/openpgp/clearsign"
import (
"bufio"
"bytes"
"crypto"
"fmt"
"hash"
"io"
"net/textproto"
"strconv"
"strings"
"golang.org/x/crypto/openpgp/armor"
"golang.org/x/crypto/openpgp/errors"
"golang.org/x/crypto/openpgp/packet"
)
// A Block represents a clearsigned message. A signature on a Block can
// be checked by passing Bytes into openpgp.CheckDetachedSignature.
type Block struct {
Headers textproto.MIMEHeader // Optional unverified Hash headers
Plaintext []byte // The original message text
Bytes []byte // The signed message
ArmoredSignature *armor.Block // The signature block
}
// start is the marker which denotes the beginning of a clearsigned message.
var start = []byte("\n-----BEGIN PGP SIGNED MESSAGE-----")
// dashEscape is prefixed to any lines that begin with a hyphen so that they
// can't be confused with endText.
var dashEscape = []byte("- ")
// endText is a marker which denotes the end of the message and the start of
// an armored signature.
var endText = []byte("-----BEGIN PGP SIGNATURE-----")
// end is a marker which denotes the end of the armored signature.
var end = []byte("\n-----END PGP SIGNATURE-----")
var crlf = []byte("\r\n")
var lf = byte('\n')
// getLine returns the first \r\n or \n delineated line from the given byte
// array. The line does not include the \r\n or \n. The remainder of the byte
// array (also not including the new line bytes) is also returned and this will
// always be smaller than the original argument.
func getLine(data []byte) (line, rest []byte) {
i := bytes.Index(data, []byte{'\n'})
var j int
if i < 0 {
i = len(data)
j = i
} else {
j = i + 1
if i > 0 && data[i-1] == '\r' {
i--
}
}
return data[0:i], data[j:]
}
// Decode finds the first clearsigned message in data and returns it, as well as
// the suffix of data which remains after the message. Any prefix data is
// discarded.
//
// If no message is found, or if the message is invalid, Decode returns nil and
// the whole data slice. The only allowed header type is Hash, and it is not
// verified against the signature hash.
func Decode(data []byte) (b *Block, rest []byte) {
// start begins with a newline. However, at the very beginning of
// the byte array, we'll accept the start string without it.
rest = data
if bytes.HasPrefix(data, start[1:]) {
rest = rest[len(start)-1:]
} else if i := bytes.Index(data, start); i >= 0 {
rest = rest[i+len(start):]
} else {
return nil, data
}
// Consume the start line and check it does not have a suffix.
suffix, rest := getLine(rest)
if len(suffix) != 0 {
return nil, data
}
var line []byte
b = &Block{
Headers: make(textproto.MIMEHeader),
}
// Next come a series of header lines.
for {
// This loop terminates because getLine's second result is
// always smaller than its argument.
if len(rest) == 0 {
return nil, data
}
// An empty line marks the end of the headers.
if line, rest = getLine(rest); len(line) == 0 {
break
}
// Reject headers with control or Unicode characters.
if i := bytes.IndexFunc(line, func(r rune) bool {
return r < 0x20 || r > 0x7e
}); i != -1 {
return nil, data
}
i := bytes.Index(line, []byte{':'})
if i == -1 {
return nil, data
}
key, val := string(line[0:i]), string(line[i+1:])
key = strings.TrimSpace(key)
if key != "Hash" {
return nil, data
}
val = strings.TrimSpace(val)
b.Headers.Add(key, val)
}
firstLine := true
for {
start := rest
line, rest = getLine(rest)
if len(line) == 0 && len(rest) == 0 {
// No armored data was found, so this isn't a complete message.
return nil, data
}
if bytes.Equal(line, endText) {
// Back up to the start of the line because armor expects to see the
// header line.
rest = start
break
}
// The final CRLF isn't included in the hash so we don't write it until
// we've seen the next line.
if firstLine {
firstLine = false
} else {
b.Bytes = append(b.Bytes, crlf...)
}
if bytes.HasPrefix(line, dashEscape) {
line = line[2:]
}
line = bytes.TrimRight(line, " \t")
b.Bytes = append(b.Bytes, line...)
b.Plaintext = append(b.Plaintext, line...)
b.Plaintext = append(b.Plaintext, lf)
}
// We want to find the extent of the armored data (including any newlines at
// the end).
i := bytes.Index(rest, end)
if i == -1 {
return nil, data
}
i += len(end)
for i < len(rest) && (rest[i] == '\r' || rest[i] == '\n') {
i++
}
armored := rest[:i]
rest = rest[i:]
var err error
b.ArmoredSignature, err = armor.Decode(bytes.NewBuffer(armored))
if err != nil {
return nil, data
}
return b, rest
}
// A dashEscaper is an io.WriteCloser which processes the body of a clear-signed
// message. The clear-signed message is written to buffered and a hash, suitable
// for signing, is maintained in h.
//
// When closed, an armored signature is created and written to complete the
// message.
type dashEscaper struct {
buffered *bufio.Writer
hashers []hash.Hash // one per key in privateKeys
hashType crypto.Hash
toHash io.Writer // writes to all the hashes in hashers
atBeginningOfLine bool
isFirstLine bool
whitespace []byte
byteBuf []byte // a one byte buffer to save allocations
privateKeys []*packet.PrivateKey
config *packet.Config
}
func (d *dashEscaper) Write(data []byte) (n int, err error) {
for _, b := range data {
d.byteBuf[0] = b
if d.atBeginningOfLine {
// The final CRLF isn't included in the hash so we have to wait
// until this point (the start of the next line) before writing it.
if !d.isFirstLine {
d.toHash.Write(crlf)
}
d.isFirstLine = false
}
// Any whitespace at the end of the line has to be removed so we
// buffer it until we find out whether there's more on this line.
if b == ' ' || b == '\t' || b == '\r' {
d.whitespace = append(d.whitespace, b)
d.atBeginningOfLine = false
continue
}
if d.atBeginningOfLine {
// At the beginning of a line, hyphens have to be escaped.
if b == '-' {
// The signature isn't calculated over the dash-escaped text so
// the escape is only written to buffered.
if _, err = d.buffered.Write(dashEscape); err != nil {
return
}
d.toHash.Write(d.byteBuf)
d.atBeginningOfLine = false
} else if b == '\n' {
// Nothing to do because we delay writing CRLF to the hash.
} else {
d.toHash.Write(d.byteBuf)
d.atBeginningOfLine = false
}
if err = d.buffered.WriteByte(b); err != nil {
return
}
} else {
if b == '\n' {
// We got a raw \n. Drop any trailing whitespace and write a
// CRLF.
d.whitespace = d.whitespace[:0]
// We delay writing CRLF to the hash until the start of the
// next line.
if err = d.buffered.WriteByte(b); err != nil {
return
}
d.atBeginningOfLine = true
} else {
// Any buffered whitespace wasn't at the end of the line so
// we need to write it out.
if len(d.whitespace) > 0 {
d.toHash.Write(d.whitespace)
if _, err = d.buffered.Write(d.whitespace); err != nil {
return
}
d.whitespace = d.whitespace[:0]
}
d.toHash.Write(d.byteBuf)
if err = d.buffered.WriteByte(b); err != nil {
return
}
}
}
}
n = len(data)
return
}
func (d *dashEscaper) Close() (err error) {
if !d.atBeginningOfLine {
if err = d.buffered.WriteByte(lf); err != nil {
return
}
}
out, err := armor.Encode(d.buffered, "PGP SIGNATURE", nil)
if err != nil {
return
}
t := d.config.Now()
for i, k := range d.privateKeys {
sig := new(packet.Signature)
sig.SigType = packet.SigTypeText
sig.PubKeyAlgo = k.PubKeyAlgo
sig.Hash = d.hashType
sig.CreationTime = t
sig.IssuerKeyId = &k.KeyId
if err = sig.Sign(d.hashers[i], k, d.config); err != nil {
return
}
if err = sig.Serialize(out); err != nil {
return
}
}
if err = out.Close(); err != nil {
return
}
if err = d.buffered.Flush(); err != nil {
return
}
return
}
// Encode returns a WriteCloser which will clear-sign a message with privateKey
// and write it to w. If config is nil, sensible defaults are used.
func Encode(w io.Writer, privateKey *packet.PrivateKey, config *packet.Config) (plaintext io.WriteCloser, err error) {
return EncodeMulti(w, []*packet.PrivateKey{privateKey}, config)
}
// EncodeMulti returns a WriteCloser which will clear-sign a message with all the
// private keys indicated and write it to w. If config is nil, sensible defaults
// are used.
func EncodeMulti(w io.Writer, privateKeys []*packet.PrivateKey, config *packet.Config) (plaintext io.WriteCloser, err error) {
for _, k := range privateKeys {
if k.Encrypted {
return nil, errors.InvalidArgumentError(fmt.Sprintf("signing key %s is encrypted", k.KeyIdString()))
}
}
hashType := config.Hash()
name := nameOfHash(hashType)
if len(name) == 0 {
return nil, errors.UnsupportedError("unknown hash type: " + strconv.Itoa(int(hashType)))
}
if !hashType.Available() {
return nil, errors.UnsupportedError("unsupported hash type: " + strconv.Itoa(int(hashType)))
}
var hashers []hash.Hash
var ws []io.Writer
for range privateKeys {
h := hashType.New()
hashers = append(hashers, h)
ws = append(ws, h)
}
toHash := io.MultiWriter(ws...)
buffered := bufio.NewWriter(w)
// start has a \n at the beginning that we don't want here.
if _, err = buffered.Write(start[1:]); err != nil {
return
}
if err = buffered.WriteByte(lf); err != nil {
return
}
if _, err = buffered.WriteString("Hash: "); err != nil {
return
}
if _, err = buffered.WriteString(name); err != nil {
return
}
if err = buffered.WriteByte(lf); err != nil {
return
}
if err = buffered.WriteByte(lf); err != nil {
return
}
plaintext = &dashEscaper{
buffered: buffered,
hashers: hashers,
hashType: hashType,
toHash: toHash,
atBeginningOfLine: true,
isFirstLine: true,
byteBuf: make([]byte, 1),
privateKeys: privateKeys,
config: config,
}
return
}
// nameOfHash returns the OpenPGP name for the given hash, or the empty string
// if the name isn't known. See RFC 4880, section 9.4.
func nameOfHash(h crypto.Hash) string {
switch h {
case crypto.MD5:
return "MD5"
case crypto.SHA1:
return "SHA1"
case crypto.RIPEMD160:
return "RIPEMD160"
case crypto.SHA224:
return "SHA224"
case crypto.SHA256:
return "SHA256"
case crypto.SHA384:
return "SHA384"
case crypto.SHA512:
return "SHA512"
}
return ""
}