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crypto: Clarify slice usage for Encrypt/Decrypt

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This commit is contained in:
Alexander Neumann 2015-04-19 13:34:42 +02:00
parent 63e79539e9
commit 8e867817a5
2 changed files with 20 additions and 10 deletions
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16
crypto/crypto.go
View File

@ -206,14 +206,15 @@ func (k *EncryptionKey) UnmarshalJSON(data []byte) error {
// Encrypt encrypts and signs data. Stored in ciphertext is IV || Ciphertext ||
// MAC. Encrypt returns the new ciphertext slice, which is extended when
// necessary. ciphertext and plaintext may point to the same slice.
// necessary. ciphertext and plaintext may not point to (exactly) the same
// slice or non-intersecting slices.
func Encrypt(ks *Key, ciphertext, plaintext []byte) ([]byte, error) {
// extend ciphertext slice if necessary
if cap(ciphertext) < len(plaintext)+Extension {
ciphertext = ciphertext[:cap(ciphertext)]
if len(ciphertext) < len(plaintext)+Extension {
ext := len(plaintext) + Extension - cap(ciphertext)
n := len(ciphertext)
ciphertext = append(ciphertext, make([]byte, ext)...)
ciphertext = ciphertext[:n]
ciphertext = ciphertext[:cap(ciphertext)]
}
iv := newIV()
@ -224,18 +225,21 @@ func Encrypt(ks *Key, ciphertext, plaintext []byte) ([]byte, error) {
e := cipher.NewCTR(c, iv[:])
e.XORKeyStream(ciphertext[ivSize:cap(ciphertext)], plaintext)
e.XORKeyStream(ciphertext[ivSize:], plaintext)
copy(ciphertext, iv[:])
// truncate to only conver iv and actual ciphertext
ciphertext = ciphertext[:ivSize+len(plaintext)]
mac := poly1305Sign(ciphertext[ivSize:], ciphertext[:ivSize], &ks.Sign)
// append the mac tag
ciphertext = append(ciphertext, mac...)
return ciphertext, nil
}
// Decrypt verifies and decrypts the ciphertext. Ciphertext must be in the form
// IV || Ciphertext || MAC.
// IV || Ciphertext || MAC. plaintext and ciphertext may point to (exactly) the
// same slice.
func Decrypt(ks *Key, plaintext, ciphertext []byte) ([]byte, error) {
// check for plausible length
if len(ciphertext) < ivSize+macSize {

14
crypto/crypto_test.go
View File

@ -31,9 +31,15 @@ func TestEncryptDecrypt(t *testing.T) {
ciphertext, err := crypto.Encrypt(k, restic.GetChunkBuf("TestEncryptDecrypt"), data)
OK(t, err)
Assert(t, len(ciphertext) == len(data)+crypto.Extension,
"ciphertext length does not match: want %d, got %d",
len(data)+crypto.Extension, len(ciphertext))
plaintext, err := crypto.Decrypt(k, nil, ciphertext)
OK(t, err)
Assert(t, len(plaintext) == len(data),
"plaintext length does not match: want %d, got %d",
len(data), len(plaintext))
restic.FreeChunkBuf("TestEncryptDecrypt", ciphertext)
@ -54,7 +60,7 @@ func TestSmallBuffer(t *testing.T) {
ciphertext := make([]byte, size/2)
ciphertext, err = crypto.Encrypt(k, ciphertext, data)
// this must throw an error, since the target slice is too small
// this must extend the slice
Assert(t, cap(ciphertext) > size/2,
"expected extended slice, but capacity is only %d bytes",
cap(ciphertext))
@ -77,12 +83,12 @@ func TestSameBuffer(t *testing.T) {
_, err = io.ReadFull(f, data)
OK(t, err)
ciphertext := make([]byte, size)
copy(ciphertext, data)
ciphertext := make([]byte, 0, size+crypto.Extension)
ciphertext, err = crypto.Encrypt(k, ciphertext, ciphertext)
ciphertext, err = crypto.Encrypt(k, ciphertext, data)
OK(t, err)
// use the same buffer for decryption
ciphertext, err = crypto.Decrypt(k, ciphertext, ciphertext)
OK(t, err)
Assert(t, bytes.Equal(ciphertext, data),