347 lines
8.8 KiB
Go
347 lines
8.8 KiB
Go
// Modified by 42wim
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//
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// Copyright 2009 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 pem implements the PEM data encoding, which originated in Privacy
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// Enhanced Mail. The most common use of PEM encoding today is in TLS keys and
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// certificates. See RFC 1421.
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package pem
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import (
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"bytes"
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"encoding/base64"
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"errors"
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"io"
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"sort"
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"strings"
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)
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// A Block represents a PEM encoded 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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// base64-encoded Bytes
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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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type Block struct {
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Type string // The type, taken from the preamble (i.e. "RSA PRIVATE KEY").
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Headers map[string]string // Optional headers.
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Bytes []byte // The decoded bytes of the contents. Typically a DER encoded ASN.1 structure.
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}
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// getLine results the first \r\n or \n delineated line from the given byte
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// array. The line does not include trailing whitespace or the trailing new
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// line bytes. The remainder of the byte array (also not including the new line
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// bytes) is also returned and this will always be smaller than the original
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// argument.
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func getLine(data []byte) (line, rest []byte) {
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i := bytes.IndexByte(data, '\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 bytes.TrimRight(data[0:i], " \t"), data[j:]
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}
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// removeSpacesAndTabs returns a copy of its input with all spaces and tabs
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// removed, if there were any. Otherwise, the input is returned unchanged.
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//
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// The base64 decoder already skips newline characters, so we don't need to
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// filter them out here.
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func removeSpacesAndTabs(data []byte) []byte {
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if !bytes.ContainsAny(data, " \t") {
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// Fast path; most base64 data within PEM contains newlines, but
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// no spaces nor tabs. Skip the extra alloc and work.
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return data
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}
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result := make([]byte, len(data))
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n := 0
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for _, b := range data {
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if b == ' ' || b == '\t' {
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continue
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}
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result[n] = b
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n++
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}
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return result[0:n]
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}
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var (
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pemStart = []byte("\n-----BEGIN ")
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pemEnd = []byte("\n-----END ")
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pemEndOfLine = []byte("-----")
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)
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// Decode will find the next PEM formatted block (certificate, private key
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// etc) in the input. It returns that block and the remainder of the input. If
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// no PEM data is found, p is nil and the whole of the input is returned in
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// rest.
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func Decode(data []byte) (p *Block, rest []byte) {
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// pemStart 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, pemStart[1:]) {
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rest = rest[len(pemStart)-1 : len(data)]
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} else if i := bytes.Index(data, pemStart); i >= 0 {
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rest = rest[i+len(pemStart) : len(data)]
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} else {
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return nil, data
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}
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typeLine, rest := getLine(rest)
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if !bytes.HasSuffix(typeLine, pemEndOfLine) {
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return decodeError(data, rest)
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}
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typeLine = typeLine[0 : len(typeLine)-len(pemEndOfLine)]
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p = &Block{
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Headers: make(map[string]string),
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Type: string(typeLine),
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}
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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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line, next := getLine(rest)
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i := bytes.IndexByte(line, ':')
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if i == -1 {
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break
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}
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// TODO(agl): need to cope with values that spread across lines.
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key, val := line[:i], line[i+1:]
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key = bytes.TrimSpace(key)
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val = bytes.TrimSpace(val)
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p.Headers[string(key)] = string(val)
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rest = next
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}
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var endIndex, endTrailerIndex int
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// If there were no headers, the END line might occur
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// immediately, without a leading newline.
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if len(p.Headers) == 0 && bytes.HasPrefix(rest, pemEnd[1:]) {
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endIndex = 0
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endTrailerIndex = len(pemEnd) - 1
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} else {
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endIndex = bytes.Index(rest, pemEnd)
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endTrailerIndex = endIndex + len(pemEnd)
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}
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if endIndex < 0 {
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return decodeError(data, rest)
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}
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// After the "-----" of the ending line, there should be the same type
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// and then a final five dashes.
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endTrailer := rest[endTrailerIndex:]
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endTrailerLen := len(typeLine) + len(pemEndOfLine)
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if len(endTrailer) < endTrailerLen {
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return decodeError(data, rest)
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}
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restOfEndLine := endTrailer[endTrailerLen:]
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endTrailer = endTrailer[:endTrailerLen]
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if !bytes.HasPrefix(endTrailer, typeLine) ||
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!bytes.HasSuffix(endTrailer, pemEndOfLine) {
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return decodeError(data, rest)
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}
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// The line must end with only whitespace.
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if s, _ := getLine(restOfEndLine); len(s) != 0 {
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return decodeError(data, rest)
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}
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base64Data := removeSpacesAndTabs(rest[:endIndex])
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p.Bytes = make([]byte, base64.StdEncoding.DecodedLen(len(base64Data)))
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n, err := base64.StdEncoding.Decode(p.Bytes, base64Data)
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if err != nil {
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return decodeError(data, rest)
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}
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p.Bytes = p.Bytes[:n]
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// the -1 is because we might have only matched pemEnd without the
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// leading newline if the PEM block was empty.
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_, rest = getLine(rest[endIndex+len(pemEnd)-1:])
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return
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}
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func decodeError(data, rest []byte) (*Block, []byte) {
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// If we get here then we have rejected a likely looking, but
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// ultimately invalid PEM block. We need to start over from a new
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// position. We have consumed the preamble line and will have consumed
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// any lines which could be header lines. However, a valid preamble
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// line is not a valid header line, therefore we cannot have consumed
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// the preamble line for the any subsequent block. Thus, we will always
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// find any valid block, no matter what bytes precede it.
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//
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// For example, if the input is
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//
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// -----BEGIN MALFORMED BLOCK-----
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// junk that may look like header lines
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// or data lines, but no END line
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//
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// -----BEGIN ACTUAL BLOCK-----
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// realdata
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// -----END ACTUAL BLOCK-----
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//
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// we've failed to parse using the first BEGIN line
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// and now will try again, using the second BEGIN line.
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p, rest := Decode(rest)
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if p == nil {
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rest = data
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}
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return p, rest
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}
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// https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.sshsig#L20-L21
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// Should be on 76 chars, but strangely enough ssh breaks on 70
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const pemLineLength = 70
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type lineBreaker struct {
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line [pemLineLength]byte
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used int
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out io.Writer
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}
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var nl = []byte{'\n'}
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func (l *lineBreaker) Write(b []byte) (n int, err error) {
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if l.used+len(b) < pemLineLength {
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copy(l.line[l.used:], b)
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l.used += len(b)
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return len(b), nil
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}
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n, err = l.out.Write(l.line[0:l.used])
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if err != nil {
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return
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}
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excess := pemLineLength - l.used
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l.used = 0
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n, err = l.out.Write(b[0:excess])
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if err != nil {
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return
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}
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n, err = l.out.Write(nl)
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if err != nil {
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return
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}
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return l.Write(b[excess:])
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}
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func (l *lineBreaker) Close() (err error) {
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if l.used > 0 {
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_, err = l.out.Write(l.line[0:l.used])
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if err != nil {
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return
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}
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_, err = l.out.Write(nl)
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}
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return
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}
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func writeHeader(out io.Writer, k, v string) error {
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_, err := out.Write([]byte(k + ": " + v + "\n"))
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return err
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}
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// Encode writes the PEM encoding of b to out.
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func Encode(out io.Writer, b *Block) error {
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// Check for invalid block before writing any output.
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for k := range b.Headers {
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if strings.Contains(k, ":") {
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return errors.New("pem: cannot encode a header key that contains a colon")
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}
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}
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// All errors below are relayed from underlying io.Writer,
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// so it is now safe to write data.
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if _, err := out.Write(pemStart[1:]); err != nil {
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return err
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}
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if _, err := out.Write([]byte(b.Type + "-----\n")); err != nil {
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return err
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}
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if len(b.Headers) > 0 {
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const procType = "Proc-Type"
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h := make([]string, 0, len(b.Headers))
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hasProcType := false
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for k := range b.Headers {
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if k == procType {
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hasProcType = true
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continue
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}
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h = append(h, k)
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}
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// The Proc-Type header must be written first.
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// See RFC 1421, section 4.6.1.1
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if hasProcType {
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if err := writeHeader(out, procType, b.Headers[procType]); err != nil {
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return err
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}
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}
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// For consistency of output, write other headers sorted by key.
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sort.Strings(h)
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for _, k := range h {
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if err := writeHeader(out, k, b.Headers[k]); err != nil {
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return err
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}
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}
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if _, err := out.Write(nl); err != nil {
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return err
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}
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}
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var breaker lineBreaker
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breaker.out = out
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b64 := base64.NewEncoder(base64.StdEncoding, &breaker)
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if _, err := b64.Write(b.Bytes); err != nil {
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return err
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}
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b64.Close()
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breaker.Close()
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if _, err := out.Write(pemEnd[1:]); err != nil {
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return err
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}
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_, err := out.Write([]byte(b.Type + "-----\n"))
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return err
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}
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// EncodeToMemory returns the PEM encoding of b.
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//
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// If b has invalid headers and cannot be encoded,
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// EncodeToMemory returns nil. If it is important to
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// report details about this error case, use Encode instead.
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func EncodeToMemory(b *Block) []byte {
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var buf bytes.Buffer
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if err := Encode(&buf, b); err != nil {
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return nil
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}
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return buf.Bytes()
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}
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