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// Copyright 2010 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.
// This package implements OpenPGP ASCII Armor, see RFC 4880. OpenPGP Armor is
// very similar to PEM except that it has an additional CRC checksum.
package armor
import (
"bytes"
"crypto/openpgp/error"
"encoding/base64"
"encoding/line"
"io"
"os"
)
// A Block represents an OpenPGP armored structure.
//
// The encoded form is:
// -----BEGIN Type-----
// Headers
//
// base64-encoded Bytes
// '=' base64 encoded checksum
// -----END Type-----
// where Headers is a possibly empty sequence of Key: Value lines.
//
// Since the armored data can be very large, this package presents a streaming
// interface.
type Block struct {
Type string // The type, taken from the preamble (i.e. "PGP SIGNATURE").
Header map[string]string // Optional headers.
Body io.Reader // A Reader from which the contents can be read
lReader lineReader
oReader openpgpReader
}
var ArmorCorrupt os.Error = error.StructuralError("armor invalid")
const crc24Init = 0xb704ce
const crc24Poly = 0x1864cfb
const crc24Mask = 0xffffff
// crc24 calculates the OpenPGP checksum as specified in RFC 4880, section 6.1
func crc24(crc uint32, d []byte) uint32 {
for _, b := range d {
crc ^= uint32(b) << 16
for i := 0; i < 8; i++ {
crc <<= 1
if crc&0x1000000 != 0 {
crc ^= crc24Poly
}
}
}
return crc
}
var armorStart = []byte("-----BEGIN ")
var armorEnd = []byte("-----END ")
var armorEndOfLine = []byte("-----")
// lineReader wraps a line based reader. It watches for the end of an armor
// block and records the expected CRC value.
type lineReader struct {
in *line.Reader
buf []byte
eof bool
crc uint32
}
func (l *lineReader) Read(p []byte) (n int, err os.Error) {
if l.eof {
return 0, os.EOF
}
if len(l.buf) > 0 {
n = copy(p, l.buf)
l.buf = l.buf[n:]
return
}
line, isPrefix, err := l.in.ReadLine()
if err != nil {
return
}
if isPrefix {
return 0, ArmorCorrupt
}
if len(line) == 5 && line[0] == '=' {
// This is the checksum line
var expectedBytes [3]byte
var m int
m, err = base64.StdEncoding.Decode(expectedBytes[0:], line[1:])
if m != 3 || err != nil {
return
}
l.crc = uint32(expectedBytes[0])<<16 |
uint32(expectedBytes[1])<<8 |
uint32(expectedBytes[2])
line, _, err = l.in.ReadLine()
if err != nil && err != os.EOF {
return
}
if !bytes.HasPrefix(line, armorEnd) {
return 0, ArmorCorrupt
}
l.eof = true
return 0, os.EOF
}
if len(line) != 64 {
return 0, ArmorCorrupt
}
n = copy(p, line)
bytesToSave := len(line) - n
if bytesToSave > 0 {
if cap(l.buf) < bytesToSave {
l.buf = make([]byte, 0, bytesToSave)
}
l.buf = l.buf[0:bytesToSave]
copy(l.buf, line[n:])
}
return
}
// openpgpReader passes Read calls to the underlying base64 decoder, but keeps
// a running CRC of the resulting data and checks the CRC against the value
// found by the lineReader at EOF.
type openpgpReader struct {
lReader *lineReader
b64Reader io.Reader
currentCRC uint32
}
func (r *openpgpReader) Read(p []byte) (n int, err os.Error) {
n, err = r.b64Reader.Read(p)
r.currentCRC = crc24(r.currentCRC, p[:n])
if err == os.EOF {
if r.lReader.crc != uint32(r.currentCRC&crc24Mask) {
return 0, ArmorCorrupt
}
}
return
}
// Decode reads a PGP armored block from the given Reader. It will ignore
// leading garbage. If it doesn't find a block, it will return nil, os.EOF. The
// given Reader is not usable after calling this function: an arbitary amount
// of data may have been read past the end of the block.
func Decode(in io.Reader) (p *Block, err os.Error) {
r := line.NewReader(in, 100)
var line []byte
ignoreNext := false
TryNextBlock:
p = nil
// Skip leading garbage
for {
ignoreThis := ignoreNext
line, ignoreNext, err = r.ReadLine()
if err != nil {
return
}
if ignoreNext || ignoreThis {
continue
}
line = bytes.TrimSpace(line)
if len(line) > len(armorStart)+len(armorEndOfLine) && bytes.HasPrefix(line, armorStart) {
break
}
}
p = new(Block)
p.Type = string(line[len(armorStart) : len(line)-len(armorEndOfLine)])
p.Header = make(map[string]string)
nextIsContinuation := false
var lastKey string
// Read headers
for {
isContinuation := nextIsContinuation
line, nextIsContinuation, err = r.ReadLine()
if err != nil {
p = nil
return
}
if isContinuation {
p.Header[lastKey] += string(line)
continue
}
line = bytes.TrimSpace(line)
if len(line) == 0 {
break
}
i := bytes.Index(line, []byte(": "))
if i == -1 {
goto TryNextBlock
}
lastKey = string(line[:i])
p.Header[lastKey] = string(line[i+2:])
}
p.lReader.in = r
p.oReader.currentCRC = crc24Init
p.oReader.lReader = &p.lReader
p.oReader.b64Reader = base64.NewDecoder(base64.StdEncoding, &p.lReader)
p.Body = &p.oReader
return
}
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