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220 lines
4.9 KiB
Go
220 lines
4.9 KiB
Go
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// Copyright 2010 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 armor implements OpenPGP ASCII Armor, see RFC 4880. OpenPGP Armor is
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// very similar to PEM except that it has an additional CRC checksum.
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package armor // import "golang.org/x/crypto/openpgp/armor"
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import (
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"bufio"
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"bytes"
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"encoding/base64"
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"golang.org/x/crypto/openpgp/errors"
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"io"
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)
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// A Block represents an OpenPGP armored structure.
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//
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// The encoded form is:
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// -----BEGIN Type-----
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// Headers
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//
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// base64-encoded Bytes
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// '=' base64 encoded checksum
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// -----END Type-----
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// where Headers is a possibly empty sequence of Key: Value lines.
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//
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// Since the armored data can be very large, this package presents a streaming
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// interface.
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type Block struct {
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Type string // The type, taken from the preamble (i.e. "PGP SIGNATURE").
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Header map[string]string // Optional headers.
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Body io.Reader // A Reader from which the contents can be read
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lReader lineReader
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oReader openpgpReader
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}
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var ArmorCorrupt error = errors.StructuralError("armor invalid")
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const crc24Init = 0xb704ce
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const crc24Poly = 0x1864cfb
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const crc24Mask = 0xffffff
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// crc24 calculates the OpenPGP checksum as specified in RFC 4880, section 6.1
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func crc24(crc uint32, d []byte) uint32 {
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for _, b := range d {
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crc ^= uint32(b) << 16
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for i := 0; i < 8; i++ {
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crc <<= 1
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if crc&0x1000000 != 0 {
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crc ^= crc24Poly
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}
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}
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}
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return crc
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}
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var armorStart = []byte("-----BEGIN ")
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var armorEnd = []byte("-----END ")
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var armorEndOfLine = []byte("-----")
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// lineReader wraps a line based reader. It watches for the end of an armor
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// block and records the expected CRC value.
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type lineReader struct {
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in *bufio.Reader
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buf []byte
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eof bool
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crc uint32
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}
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func (l *lineReader) Read(p []byte) (n int, err error) {
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if l.eof {
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return 0, io.EOF
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}
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if len(l.buf) > 0 {
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n = copy(p, l.buf)
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l.buf = l.buf[n:]
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return
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}
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line, isPrefix, err := l.in.ReadLine()
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if err != nil {
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return
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}
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if isPrefix {
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return 0, ArmorCorrupt
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}
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if len(line) == 5 && line[0] == '=' {
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// This is the checksum line
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var expectedBytes [3]byte
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var m int
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m, err = base64.StdEncoding.Decode(expectedBytes[0:], line[1:])
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if m != 3 || err != nil {
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return
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}
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l.crc = uint32(expectedBytes[0])<<16 |
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uint32(expectedBytes[1])<<8 |
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uint32(expectedBytes[2])
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line, _, err = l.in.ReadLine()
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if err != nil && err != io.EOF {
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return
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}
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if !bytes.HasPrefix(line, armorEnd) {
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return 0, ArmorCorrupt
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}
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l.eof = true
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return 0, io.EOF
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}
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if len(line) > 96 {
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return 0, ArmorCorrupt
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}
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n = copy(p, line)
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bytesToSave := len(line) - n
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if bytesToSave > 0 {
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if cap(l.buf) < bytesToSave {
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l.buf = make([]byte, 0, bytesToSave)
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}
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l.buf = l.buf[0:bytesToSave]
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copy(l.buf, line[n:])
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}
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return
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}
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// openpgpReader passes Read calls to the underlying base64 decoder, but keeps
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// a running CRC of the resulting data and checks the CRC against the value
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// found by the lineReader at EOF.
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type openpgpReader struct {
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lReader *lineReader
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b64Reader io.Reader
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currentCRC uint32
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}
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func (r *openpgpReader) Read(p []byte) (n int, err error) {
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n, err = r.b64Reader.Read(p)
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r.currentCRC = crc24(r.currentCRC, p[:n])
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if err == io.EOF {
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if r.lReader.crc != uint32(r.currentCRC&crc24Mask) {
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return 0, ArmorCorrupt
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}
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}
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return
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}
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// Decode reads a PGP armored block from the given Reader. It will ignore
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// leading garbage. If it doesn't find a block, it will return nil, io.EOF. The
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// given Reader is not usable after calling this function: an arbitrary amount
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// of data may have been read past the end of the block.
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func Decode(in io.Reader) (p *Block, err error) {
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r := bufio.NewReaderSize(in, 100)
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var line []byte
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ignoreNext := false
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TryNextBlock:
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p = nil
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// Skip leading garbage
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for {
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ignoreThis := ignoreNext
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line, ignoreNext, err = r.ReadLine()
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if err != nil {
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return
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}
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if ignoreNext || ignoreThis {
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continue
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}
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line = bytes.TrimSpace(line)
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if len(line) > len(armorStart)+len(armorEndOfLine) && bytes.HasPrefix(line, armorStart) {
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break
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}
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}
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p = new(Block)
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p.Type = string(line[len(armorStart) : len(line)-len(armorEndOfLine)])
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p.Header = make(map[string]string)
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nextIsContinuation := false
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var lastKey string
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// Read headers
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for {
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isContinuation := nextIsContinuation
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line, nextIsContinuation, err = r.ReadLine()
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if err != nil {
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p = nil
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return
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}
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if isContinuation {
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p.Header[lastKey] += string(line)
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continue
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}
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line = bytes.TrimSpace(line)
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if 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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goto TryNextBlock
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}
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lastKey = string(line[:i])
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p.Header[lastKey] = string(line[i+2:])
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}
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p.lReader.in = r
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p.oReader.currentCRC = crc24Init
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p.oReader.lReader = &p.lReader
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p.oReader.b64Reader = base64.NewDecoder(base64.StdEncoding, &p.lReader)
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p.Body = &p.oReader
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return
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}
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