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Clean up the API and writer code. 

Added an Example in documentation for code usage.
Cleaned up documentation and README.txt.
This commit is contained in:
alexmullins 2015-12-03 04:44:20 -06:00
parent dff173efe5
commit e1460042c2
6 changed files with 168 additions and 116 deletions
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12
README.txt
View File

@ -6,17 +6,19 @@ This package DOES NOT intend to implement the encryption methods
mentioned in the original PKWARE spec (sections 6.0 and 7.0):
https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT
The process
============
1. hello.txt -> compressed -> encrypted -> .zip
2. .zip -> decrypted -> decompressed -> hello.txt
Status - Alpha. More tests and code clean up next.
Roadmap
========
Reading - Done.
Writing - Starting.
Writing - Done.
Testing - Needs more.
The process
============
1. hello.txt -> compressed -> encrypted -> .zip
2. .zip -> decrypted -> decompressed -> hello.txt
WinZip AES specifies
=====================
1. Encryption-Decryption w/ AES-CTR (128, 192, or 256 bits)

180
crypto.go
View File

@ -26,8 +26,22 @@ const (
aes256 = 32
)
func aesKeyLen(strength byte) int {
switch strength {
case 1:
return aes128
case 2:
return aes192
case 3:
return aes256
default:
return 0
}
}
// Encryption/Decryption Errors
var (
ErrEncryption = errors.New("zip: encryption error")
ErrDecryption = errors.New("zip: decryption error")
ErrPassword = errors.New("zip: invalid password")
ErrAuthentication = errors.New("zip: authentication failed")
@ -38,12 +52,11 @@ var (
// repeatedly encrypting an incrementing counter and
// xoring the resulting stream of data with the input.
// This is a reimplementation of Go's CTR mode to allow
// for little-endian, left-aligned uint32 counter. Go's
// cipher.NewCTR follows the NIST Standard SP 800-38A, pp 13-15
// which has a big-endian, right-aligned counter. WinZip
// AES requires the CTR mode to have a little-endian,
// left-aligned counter.
// This is a re-implementation of Go's CTR mode to allow
// for a little-endian, left-aligned uint32 counter, which
// is required for WinZip AES encryption. Go's cipher.NewCTR
// follows the NIST Standard SP 800-38A, pp 13-15
// which has a big-endian, right-aligned counter.
type ctr struct {
b cipher.Block
@ -55,7 +68,7 @@ type ctr struct {
const streamBufferSize = 512
// NewWinZipCTR returns a Stream which encrypts/decrypts using the given Block in
// counter mode. The counter is initially set to 1.
// counter mode. The counter is initially set to 1 per WinZip AES.
func newWinZipCTR(block cipher.Block) cipher.Stream {
bufSize := streamBufferSize
if bufSize < block.BlockSize() {
@ -128,6 +141,29 @@ func xorBytes(dst, a, b []byte) int {
return n
}
// newAuthReader returns either a buffered or streaming authentication reader.
// Buffered authentication is recommended. Streaming authentication is only
// recommended if: 1. you buffer the data yourself and wait for authentication
// before streaming to another source such as the network, or 2. you just don't
// care about authenticating unknown ciphertext before use :).
func newAuthReader(akey []byte, data, adata io.Reader, streaming bool) io.Reader {
ar := authReader{
data: data,
adata: adata,
mac: hmac.New(sha1.New, akey),
err: nil,
auth: false,
}
if streaming {
return &ar
}
return &bufferedAuthReader{
ar,
new(bytes.Buffer),
}
}
// Streaming authentication
type authReader struct {
data io.Reader // data to be authenticated
adata io.Reader // the authentication code to read
@ -136,7 +172,6 @@ type authReader struct {
auth bool
}
// Streaming authentication
func (a *authReader) Read(p []byte) (int, error) {
if a.err != nil {
return 0, a.err
@ -173,34 +208,12 @@ func (a *authReader) Read(p []byte) (int, error) {
return n, a.err
}
// newAuthReader returns either a buffered or streaming authentication reader.
// Buffered authentication is recommended. Streaming authentication is only
// recommended if: 1. you buffer the data yourself and wait for authentication
// before streaming to another source such as the network, or 2. you just don't
// care about authenticating unknown ciphertext before use :).
func newAuthReader(akey []byte, data, adata io.Reader, streaming bool) io.Reader {
ar := authReader{
data: data,
adata: adata,
mac: hmac.New(sha1.New, akey),
err: nil,
auth: false,
}
if streaming {
return &ar
}
return &bufferedAuthReader{
ar,
new(bytes.Buffer),
}
}
// buffered authentication
type bufferedAuthReader struct {
authReader
buf *bytes.Buffer // buffer to store data to authenticate
}
// buffered authentication
func (a *bufferedAuthReader) Read(b []byte) (int, error) {
// check for sticky error
if a.err != nil {
@ -275,10 +288,10 @@ func newDecryptionReader(r *io.SectionReader, f *File) (io.Reader, error) {
salt := saltpwvv[:saltLen]
pwvv := saltpwvv[saltLen : saltLen+2]
// generate keys
if f.Password == nil {
if f.password == nil {
return nil, ErrPassword
}
decKey, authKey, pwv := generateKeys(f.Password(), salt, keyLen)
decKey, authKey, pwv := generateKeys(f.password(), salt, keyLen)
// check password verifier (pwv)
// Change to use crypto/subtle for constant time comparison
if !checkPasswordVerification(pwv, pwvv) {
@ -294,7 +307,7 @@ func newDecryptionReader(r *io.SectionReader, f *File) (io.Reader, error) {
authOff := dataOff + dataLen
authcode := io.NewSectionReader(r, authOff, 10)
// setup auth reader, (buffered)/streaming
ar := newAuthReader(authKey, data, authcode, false)
ar := newAuthReader(authKey, data, authcode, f.DeferAuth)
// return decryption reader
dr := decryptStream(decKey, ar)
if dr == nil {
@ -313,19 +326,7 @@ func decryptStream(key []byte, ciphertext io.Reader) io.Reader {
return reader
}
func aesKeyLen(strength byte) int {
switch strength {
case 1:
return aes128
case 2:
return aes192
case 3:
return aes256
default:
return 0
}
}
// writes encrypted data to hmac as it passes through
type authWriter struct {
hmac hash.Hash // from fw.hmac
w io.Writer // this will be the compCount writer
@ -344,8 +345,8 @@ type encryptionWriter struct {
pwv []byte // password verification code to be written
salt []byte // salt to be written
w io.Writer // where to write the salt + pwv
es io.Writer // where to write encrypted file data
first bool // first write?
es io.Writer // where to write plaintext
first bool // first write
err error // last error
}
@ -368,16 +369,26 @@ func (ew *encryptionWriter) Write(p []byte) (int, error) {
return ew.es.Write(p)
}
// newEncryptionWriter returns a io.Writer that when written to, 1. writes
// out the salt, 2. writes out pwv, 3. writes out encrypted the data, and finally
// 4. will write to hmac.
func encryptStream(key []byte, w io.Writer) (io.Writer, error) {
block, err := aes.NewCipher(key)
if err != nil {
return nil, errors.New("zip: couldn't create AES cipher")
}
stream := newWinZipCTR(block)
writer := &cipher.StreamWriter{S: stream, W: w}
return writer, nil
}
// newEncryptionWriter returns an io.Writer that when written to, 1. writes
// out the salt, 2. writes out pwv, and 3. writes out authenticated, encrypted
// data. The authcode will be written out in fileWriter.close().
func newEncryptionWriter(w io.Writer, fh *FileHeader, fw *fileWriter) (io.Writer, error) {
var salt [16]byte
_, err := rand.Read(salt[:])
if err != nil {
return nil, errors.New("zip: unable to generate random salt")
}
ekey, akey, pwv := generateKeys(fh.Password(), salt[:], aes256)
ekey, akey, pwv := generateKeys(fh.password(), salt[:], aes256)
fw.hmac = hmac.New(sha1.New, akey)
aw := &authWriter{
hmac: fw.hmac,
@ -397,29 +408,56 @@ func newEncryptionWriter(w io.Writer, fh *FileHeader, fw *fileWriter) (io.Writer
return ew, nil
}
func encryptStream(key []byte, w io.Writer) (io.Writer, error) {
block, err := aes.NewCipher(key)
if err != nil {
return nil, errors.New("zip: couldn't create AES cipher")
}
stream := newWinZipCTR(block)
writer := &cipher.StreamWriter{S: stream, W: w}
return writer, nil
// IsEncrypted indicates whether this file's data is encrypted.
func (h *FileHeader) IsEncrypted() bool {
return h.Flags&0x1 == 1
}
func (fh *FileHeader) writeWinZipExtra() {
// WinZip AE-2 specifies that no CRC value is written and
// should be skipped when reading.
func (h *FileHeader) isAE2() bool {
return h.ae == 2
}
func (h *FileHeader) writeWinZipExtra() {
// total size is 11 bytes
var buf [11]byte
eb := writeBuf(buf[:])
eb.uint16(winzipAesExtraId)
eb.uint16(7) // following data size is 7
eb.uint16(2) // ae 2
eb.uint16(0x4541) // "AE"
eb.uint8(3) // aes256
eb.uint16(fh.Method) // original compression method
fh.Extra = append(fh.Extra, buf[:]...)
eb.uint16(winzipAesExtraId) // 0x9901
eb.uint16(7) // following data size is 7
eb.uint16(2) // ae 2
eb.uint16(0x4541) // "AE"
eb.uint8(3) // aes256
eb.uint16(h.Method) // original compression method
h.Extra = append(h.Extra, buf[:]...)
}
func (fh *FileHeader) setEncryptionBit() {
fh.Flags |= 0x1
func (h *FileHeader) setEncryptionBit() {
h.Flags |= 0x1
}
// SetPassword sets the password used for encryption/decryption.
func (h *FileHeader) SetPassword(password string) {
if !h.IsEncrypted() {
h.setEncryptionBit()
}
h.password = func() []byte {
return []byte(password)
}
}
// PasswordFn is a function that returns the password
// as a byte slice
type passwordFn func() []byte
// Encrypt is similar to Create except that it will encrypt the file contents
// using AES-256 with the given password. Must follow all the same constraints
// as Create.
func (w *Writer) Encrypt(name string, password string) (io.Writer, error) {
fh := &FileHeader{
Name: name,
Method: Deflate,
}
fh.SetPassword(password)
return w.CreateHeader(fh)
}

24
crypto_test.go
View File

@ -7,10 +7,6 @@ import (
"testing"
)
func pwFn() []byte {
return []byte("golang")
}
// Test simple password reading.
func TestPasswordReadSimple(t *testing.T) {
file := "hello-aes.zip"
@ -30,7 +26,7 @@ func TestPasswordReadSimple(t *testing.T) {
if f.Method != 0 {
t.Errorf("Expected %s to have its Method set to 0.", file)
}
f.Password = pwFn
f.SetPassword("golang")
rc, err := f.Open()
if err != nil {
t.Errorf("Expected to open the readcloser: %v.", err)
@ -45,6 +41,7 @@ func TestPasswordReadSimple(t *testing.T) {
}
// Test for multi-file password protected zip.
// Each file can be protected with a different password.
func TestPasswordHelloWorldAes(t *testing.T) {
file := "world-aes.zip"
expecting := "helloworld"
@ -61,7 +58,7 @@ func TestPasswordHelloWorldAes(t *testing.T) {
if !f.IsEncrypted() {
t.Errorf("Expected %s to be encrypted.", f.FileInfo().Name)
}
f.Password = pwFn
f.SetPassword("golang")
rc, err := f.Open()
if err != nil {
t.Errorf("Expected to open readcloser: %v", err)
@ -91,7 +88,7 @@ func TestPasswordMacbethAct1(t *testing.T) {
if !f.IsEncrypted() {
t.Errorf("Expected %s to be encrypted.", f.Name)
}
f.Password = pwFn
f.SetPassword("golang")
rc, err := f.Open()
if err != nil {
t.Errorf("Expected to open readcloser: %v", err)
@ -131,7 +128,7 @@ func TestPasswordAE1BadCRC(t *testing.T) {
if !f.IsEncrypted() {
t.Errorf("Expected zip to be encrypted")
}
f.Password = pwFn
f.SetPassword("golang")
rc, err := f.Open()
if err != nil {
t.Errorf("Expected the readcloser to open.")
@ -162,7 +159,7 @@ func TestPasswordTamperedData(t *testing.T) {
if !f.IsEncrypted() {
t.Errorf("Expected zip to be encrypted")
}
f.Password = pwFn
f.SetPassword("golang")
rc, err := f.Open()
if err != nil {
t.Errorf("Expected the readcloser to open.")
@ -178,14 +175,9 @@ func TestPasswordWriteSimple(t *testing.T) {
contents := []byte("Hello World")
conLen := len(contents)
// Write a zip
fh := &FileHeader{
Name: "hello.txt",
Password: pwFn,
}
raw := new(bytes.Buffer)
zipw := NewWriter(raw)
w, err := zipw.CreateHeader(fh)
w, err := zipw.Encrypt("hello.txt", "golang")
if err != nil {
t.Errorf("Expected to create a new FileHeader")
}
@ -206,7 +198,7 @@ func TestPasswordWriteSimple(t *testing.T) {
t.Errorf("Expected to have one file in the zip archive, but has %d files", nn)
}
z := zipr.File[0]
z.Password = pwFn
z.SetPassword("golang")
rr, err := z.Open()
if err != nil {
t.Errorf("Expected to open the readcloser: %v", err)

40
example_test.go
View File

@ -58,9 +58,6 @@ func ExampleReader() {
// Iterate through the files in the archive,
// printing some of their contents.
for _, f := range r.File {
// if f.IsEncrypted() {
// f.SetPassword([]byte("password"))
// }
fmt.Printf("Contents of %s:\n", f.Name)
rc, err := f.Open()
if err != nil {
@ -77,3 +74,40 @@ func ExampleReader() {
// Contents of README:
// This is the source code repository for the Go programming language.
}
func ExampleWriter_Encrypt() {
contents := []byte("Hello World")
// write a password zip
raw := new(bytes.Buffer)
zipw := zip.NewWriter(raw)
w, err := zipw.Encrypt("hello.txt", "golang")
if err != nil {
log.Fatal(err)
}
_, err = io.Copy(w, bytes.NewReader(contents))
if err != nil {
log.Fatal(err)
}
zipw.Close()
// read the password zip
zipr, err := zip.NewReader(bytes.NewReader(raw.Bytes()), int64(raw.Len()))
if err != nil {
log.Fatal(err)
}
for _, z := range zipr.File {
z.SetPassword("golang")
rr, err := z.Open()
if err != nil {
log.Fatal(err)
}
_, err = io.Copy(os.Stdout, rr)
if err != nil {
log.Fatal(err)
}
rr.Close()
}
// Output:
// Hello World
}

24
struct.go
View File

@ -17,7 +17,7 @@ for normal archives both fields will be the same. For files requiring
the ZIP64 format the 32 bit fields will be 0xffffffff and the 64 bit
fields must be used instead.
Can read/write AES encrypted files that use Winzip's AES encryption method.
Can read/write password protected files that use Winzip's AES encryption method.
See: http://www.winzip.com/aes_info.htm
*/
package zip
@ -93,31 +93,19 @@ type FileHeader struct {
ExternalAttrs uint32 // Meaning depends on CreatorVersion
Comment string
// DeferAuth determines whether hmac checks happen before
// any ciphertext is decrypted. It is recommended to leave this
// set to false. For more detail:
// DeferAuth being set to true will delay hmac auth/integrity
// checks when decrypting a file meaning the reader will be
// getting unauthenticated plaintext. It is recommended to leave
// this set to false. For more detail:
// https://www.imperialviolet.org/2014/06/27/streamingencryption.html
// https://www.imperialviolet.org/2015/05/16/aeads.html
DeferAuth bool
Password PasswordFn // Returns the password to use when reading/writing
password passwordFn // Returns the password to use when reading/writing
ae uint16
aesStrength byte
}
// PasswordFn is a function that returns the password
// as a byte slice
type PasswordFn func() []byte
// IsEncrypted indicates whether this file's data is encrypted.
func (f *FileHeader) IsEncrypted() bool {
return f.Flags&0x1 == 1
}
func (f *FileHeader) isAE2() bool {
return f.ae == 2
}
// FileInfo returns an os.FileInfo for the FileHeader.
func (h *FileHeader) FileInfo() os.FileInfo {
return headerFileInfo{h}

4
writer.go
View File

@ -228,10 +228,8 @@ func (w *Writer) CreateHeader(fh *FileHeader) (io.Writer, error) {
}
// check for password
var sw io.Writer = fw.compCount
if fh.Password != nil {
if fh.password != nil {
// we have a password and need to encrypt.
// 1. Set encryption bit in fh.Flags
fh.setEncryptionBit()
fh.writeWinZipExtra()
fh.Method = 99 // ok to change, we've gotten the comp and wrote extra
ew, err := newEncryptionWriter(sw, fh, fw)