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