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crypto/cipher: add resync open to OCFB mode.

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OpenPGP changed its OCFB mode for more modern packets (for example, the
MDC symmetrically encrypted packet). This change adds a bool to
determine which mode is used.

R=bradfitzgo, r, rsc
CC=golang-dev
https://golang.org/cl/4126041
This commit is contained in:
Adam Langley 2011-02-03 09:17:42 -05:00
parent 31ccf19612
commit fc5c1f0a18
2 changed files with 41 additions and 12 deletions
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32
src/pkg/crypto/cipher/ocfb.go
View File

@ -12,11 +12,21 @@ type ocfbEncrypter struct {
outUsed int
}
// An OCFBResyncOption determines if the "resynchronization step" of OCFB is
// performed.
type OCFBResyncOption bool
const (
OCFBResync OCFBResyncOption = true
OCFBNoResync OCFBResyncOption = false
)
// NewOCFBEncrypter returns a Stream which encrypts data with OpenPGP's cipher
// feedback mode using the given Block, and an initial amount of ciphertext.
// randData must be random bytes and be the same length as the Block's block
// size.
func NewOCFBEncrypter(block Block, randData []byte) (Stream, []byte) {
// size. Resync determines if the "resynchronization step" from RFC 4880, 13.9
// step 7 is performed. Different parts of OpenPGP vary on this point.
func NewOCFBEncrypter(block Block, randData []byte, resync OCFBResyncOption) (Stream, []byte) {
blockSize := block.BlockSize()
if len(randData) != blockSize {
return nil, nil
@ -38,7 +48,13 @@ func NewOCFBEncrypter(block Block, randData []byte) (Stream, []byte) {
prefix[blockSize] = x.fre[0] ^ randData[blockSize-2]
prefix[blockSize+1] = x.fre[1] ^ randData[blockSize-1]
if resync {
block.Encrypt(x.fre, prefix[2:])
} else {
x.fre[0] = prefix[blockSize]
x.fre[1] = prefix[blockSize+1]
x.outUsed = 2
}
return x, prefix
}
@ -64,8 +80,10 @@ type ocfbDecrypter struct {
// NewOCFBDecrypter returns a Stream which decrypts data with OpenPGP's cipher
// feedback mode using the given Block. Prefix must be the first blockSize + 2
// bytes of the ciphertext, where blockSize is the Block's block size. If an
// incorrect key is detected then nil is returned.
func NewOCFBDecrypter(block Block, prefix []byte) Stream {
// incorrect key is detected then nil is returned. Resync determines if the
// "resynchronization step" from RFC 4880, 13.9 step 7 is performed. Different
// parts of OpenPGP vary on this point.
func NewOCFBDecrypter(block Block, prefix []byte, resync OCFBResyncOption) Stream {
blockSize := block.BlockSize()
if len(prefix) != blockSize+2 {
return nil
@ -93,7 +111,13 @@ func NewOCFBDecrypter(block Block, prefix []byte) Stream {
return nil
}
if resync {
block.Encrypt(x.fre, prefix[2:])
} else {
x.fre[0] = prefix[blockSize]
x.fre[1] = prefix[blockSize+1]
x.outUsed = 2
}
return x
}

17
src/pkg/crypto/cipher/ocfb_test.go
View File

@ -11,29 +11,34 @@ import (
"testing"
)
func TestOCFB(t *testing.T) {
func testOCFB(t *testing.T, resync OCFBResyncOption) {
block, err := aes.NewCipher(commonKey128)
if err != nil {
t.Error(err)
return
}
plaintext := []byte("this is the plaintext")
plaintext := []byte("this is the plaintext, which is long enough to span several blocks.")
randData := make([]byte, block.BlockSize())
rand.Reader.Read(randData)
ocfb, prefix := NewOCFBEncrypter(block, randData)
ocfb, prefix := NewOCFBEncrypter(block, randData, resync)
ciphertext := make([]byte, len(plaintext))
ocfb.XORKeyStream(ciphertext, plaintext)
ocfbdec := NewOCFBDecrypter(block, prefix)
ocfbdec := NewOCFBDecrypter(block, prefix, resync)
if ocfbdec == nil {
t.Error("NewOCFBDecrypter failed")
t.Error("NewOCFBDecrypter failed (resync: %t)", resync)
return
}
plaintextCopy := make([]byte, len(plaintext))
ocfbdec.XORKeyStream(plaintextCopy, ciphertext)
if !bytes.Equal(plaintextCopy, plaintext) {
t.Errorf("got: %x, want: %x", plaintextCopy, plaintext)
t.Errorf("got: %x, want: %x (resync: %t)", plaintextCopy, plaintext, resync)
}
}
func TestOCFB(t *testing.T) {
testOCFB(t, OCFBNoResync)
testOCFB(t, OCFBResync)
}