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crypto/cipher: add NewGCMWithNonceAndTagSize for custom tag sizes. 

GCM allows using tag sizes smaller than the block size. This adds a
NewGCMWithNonceAndTagSize function which allows specifying the tag
size.

Fixes #19594

Change-Id: Ib2008c6f13ad6d916638b1523c0ded8a80eaf42d
Reviewed-on: https://go-review.googlesource.com/48510
Reviewed-by: Filippo Valsorda <hi@filippo.io>
Run-TryBot: Filippo Valsorda <hi@filippo.io>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Conrado Gouvea 2017-07-13 22:14:37 -03:00 committed by Brad Fitzpatrick
parent c0094338fb
commit 8cb4327ea3
6 changed files with 134 additions and 42 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
src/crypto/aes/aes_gcm.go
View File

@ -36,6 +36,7 @@ func gcmAesFinish(productTable *[256]byte, tagMask, T *[16]byte, pLen, dLen uint
const (
gcmBlockSize = 16
gcmTagSize = 16
gcmMinimumTagSize = 12 // NIST SP 800-38D recommends tags with 12 or more bytes.
gcmStandardNonceSize = 12
)
@ -53,8 +54,8 @@ var _ gcmAble = (*aesCipherGCM)(nil)
// NewGCM returns the AES cipher wrapped in Galois Counter Mode. This is only
// called by crypto/cipher.NewGCM via the gcmAble interface.
func (c *aesCipherGCM) NewGCM(nonceSize int) (cipher.AEAD, error) {
g := &gcmAsm{ks: c.enc, nonceSize: nonceSize}
func (c *aesCipherGCM) NewGCM(nonceSize, tagSize int) (cipher.AEAD, error) {
g := &gcmAsm{ks: c.enc, nonceSize: nonceSize, tagSize: tagSize}
gcmAesInit(&g.productTable, g.ks)
return g, nil
}
@ -68,14 +69,16 @@ type gcmAsm struct {
productTable [256]byte
// nonceSize contains the expected size of the nonce, in bytes.
nonceSize int
// tagSize contains the size of the tag, in bytes.
tagSize int
}
func (g *gcmAsm) NonceSize() int {
return g.nonceSize
}
func (*gcmAsm) Overhead() int {
return gcmTagSize
func (g *gcmAsm) Overhead() int {
return g.tagSize
}
// sliceForAppend takes a slice and a requested number of bytes. It returns a
@ -120,7 +123,7 @@ func (g *gcmAsm) Seal(dst, nonce, plaintext, data []byte) []byte {
var tagOut [gcmTagSize]byte
gcmAesData(&g.productTable, data, &tagOut)
ret, out := sliceForAppend(dst, len(plaintext)+gcmTagSize)
ret, out := sliceForAppend(dst, len(plaintext)+g.tagSize)
if len(plaintext) > 0 {
gcmAesEnc(&g.productTable, out, plaintext, &counter, &tagOut, g.ks)
}
@ -136,16 +139,21 @@ func (g *gcmAsm) Open(dst, nonce, ciphertext, data []byte) ([]byte, error) {
if len(nonce) != g.nonceSize {
panic("cipher: incorrect nonce length given to GCM")
}
// Sanity check to prevent the authentication from always succeeding if an implementation
// leaves tagSize uninitialized, for example.
if g.tagSize < gcmMinimumTagSize {
panic("cipher: incorrect GCM tag size")
}
if len(ciphertext) < gcmTagSize {
if len(ciphertext) < g.tagSize {
return nil, errOpen
}
if uint64(len(ciphertext)) > ((1<<32)-2)*BlockSize+gcmTagSize {
if uint64(len(ciphertext)) > ((1<<32)-2)*uint64(BlockSize)+uint64(g.tagSize) {
return nil, errOpen
}
tag := ciphertext[len(ciphertext)-gcmTagSize:]
ciphertext = ciphertext[:len(ciphertext)-gcmTagSize]
tag := ciphertext[len(ciphertext)-g.tagSize:]
ciphertext = ciphertext[:len(ciphertext)-g.tagSize]
// See GCM spec, section 7.1.
var counter, tagMask [gcmBlockSize]byte
@ -171,7 +179,7 @@ func (g *gcmAsm) Open(dst, nonce, ciphertext, data []byte) ([]byte, error) {
}
gcmAesFinish(&g.productTable, &tagMask, &expectedTag, uint64(len(ciphertext)), uint64(len(data)))
if subtle.ConstantTimeCompare(expectedTag[:], tag) != 1 {
if subtle.ConstantTimeCompare(expectedTag[:g.tagSize], tag) != 1 {
for i := range out {
out[i] = 0
}

46
src/crypto/aes/gcm_s390x.go
View File

@ -58,11 +58,13 @@ type gcmAsm struct {
block *aesCipherAsm
hashKey gcmHashKey
nonceSize int
tagSize int
}
const (
gcmBlockSize = 16
gcmTagSize = 16
gcmMinimumTagSize = 12 // NIST SP 800-38D recommends tags with 12 or more bytes.
gcmStandardNonceSize = 12
)
@ -73,13 +75,14 @@ var _ gcmAble = (*aesCipherAsm)(nil)
// NewGCM returns the AES cipher wrapped in Galois Counter Mode. This is only
// called by crypto/cipher.NewGCM via the gcmAble interface.
func (c *aesCipherAsm) NewGCM(nonceSize int) (cipher.AEAD, error) {
func (c *aesCipherAsm) NewGCM(nonceSize, tagSize int) (cipher.AEAD, error) {
var hk gcmHashKey
c.Encrypt(hk[:], hk[:])
g := gcmAsm{
block: c,
hashKey: hk,
nonceSize: nonceSize,
tagSize: tagSize,
}
if hasKMA {
g := gcmKMA{g}
@ -92,8 +95,8 @@ func (g *gcmAsm) NonceSize() int {
return g.nonceSize
}
func (*gcmAsm) Overhead() int {
return gcmTagSize
func (g *gcmAsm) Overhead() int {
return g.tagSize
}
// sliceForAppend takes a slice and a requested number of bytes. It returns a
@ -222,7 +225,7 @@ func (g *gcmAsm) Seal(dst, nonce, plaintext, data []byte) []byte {
panic("cipher: message too large for GCM")
}
ret, out := sliceForAppend(dst, len(plaintext)+gcmTagSize)
ret, out := sliceForAppend(dst, len(plaintext)+g.tagSize)
counter := g.deriveCounter(nonce)
@ -230,8 +233,10 @@ func (g *gcmAsm) Seal(dst, nonce, plaintext, data []byte) []byte {
g.block.Encrypt(tagMask[:], counter[:])
counter.inc()
var tagOut [gcmTagSize]byte
g.counterCrypt(out, plaintext, &counter)
g.auth(out[len(plaintext):], out[:len(plaintext)], data, &tagMask)
g.auth(tagOut[:], out[:len(plaintext)], data, &tagMask)
copy(out[len(plaintext):], tagOut[:])
return ret
}
@ -242,15 +247,20 @@ func (g *gcmAsm) Open(dst, nonce, ciphertext, data []byte) ([]byte, error) {
if len(nonce) != g.nonceSize {
panic("cipher: incorrect nonce length given to GCM")
}
if len(ciphertext) < gcmTagSize {
// Sanity check to prevent the authentication from always succeeding if an implementation
// leaves tagSize uninitialized, for example.
if g.tagSize < gcmMinimumTagSize {
panic("cipher: incorrect GCM tag size")
}
if len(ciphertext) < g.tagSize {
return nil, errOpen
}
if uint64(len(ciphertext)) > ((1<<32)-2)*BlockSize+gcmTagSize {
if uint64(len(ciphertext)) > ((1<<32)-2)*uint64(BlockSize)+uint64(g.tagSize) {
return nil, errOpen
}
tag := ciphertext[len(ciphertext)-gcmTagSize:]
ciphertext = ciphertext[:len(ciphertext)-gcmTagSize]
tag := ciphertext[len(ciphertext)-g.tagSize:]
ciphertext = ciphertext[:len(ciphertext)-g.tagSize]
counter := g.deriveCounter(nonce)
@ -263,7 +273,7 @@ func (g *gcmAsm) Open(dst, nonce, ciphertext, data []byte) ([]byte, error) {
ret, out := sliceForAppend(dst, len(ciphertext))
if subtle.ConstantTimeCompare(expectedTag[:], tag) != 1 {
if subtle.ConstantTimeCompare(expectedTag[:g.tagSize], tag) != 1 {
// The AESNI code decrypts and authenticates concurrently, and
// so overwrites dst in the event of a tag mismatch. That
// behavior is mimicked here in order to be consistent across
@ -316,7 +326,7 @@ func (g *gcmKMA) Seal(dst, nonce, plaintext, data []byte) []byte {
panic("cipher: message too large for GCM")
}
ret, out := sliceForAppend(dst, len(plaintext)+gcmTagSize)
ret, out := sliceForAppend(dst, len(plaintext)+g.tagSize)
counter := g.deriveCounter(nonce)
fc := g.block.function | kmaLAAD | kmaLPC
@ -334,24 +344,28 @@ func (g *gcmKMA) Open(dst, nonce, ciphertext, data []byte) ([]byte, error) {
if len(nonce) != g.nonceSize {
panic("cipher: incorrect nonce length given to GCM")
}
if len(ciphertext) < gcmTagSize {
if len(ciphertext) < g.tagSize {
return nil, errOpen
}
if uint64(len(ciphertext)) > ((1<<32)-2)*BlockSize+gcmTagSize {
if uint64(len(ciphertext)) > ((1<<32)-2)*uint64(BlockSize)+uint64(g.tagSize) {
return nil, errOpen
}
tag := ciphertext[len(ciphertext)-gcmTagSize:]
ciphertext = ciphertext[:len(ciphertext)-gcmTagSize]
tag := ciphertext[len(ciphertext)-g.tagSize:]
ciphertext = ciphertext[:len(ciphertext)-g.tagSize]
ret, out := sliceForAppend(dst, len(ciphertext))
if g.tagSize < gcmMinimumTagSize {
panic("cipher: incorrect GCM tag size")
}
counter := g.deriveCounter(nonce)
fc := g.block.function | kmaLAAD | kmaLPC | kmaDecrypt
var expectedTag [gcmTagSize]byte
kmaGCM(fc, g.block.key, out[:len(ciphertext)], ciphertext, data, &expectedTag, &counter)
if subtle.ConstantTimeCompare(expectedTag[:], tag) != 1 {
if subtle.ConstantTimeCompare(expectedTag[:g.tagSize], tag) != 1 {
// The AESNI code decrypts and authenticates concurrently, and
// so overwrites dst in the event of a tag mismatch. That
// behavior is mimicked here in order to be consistent across

2
src/crypto/aes/modes.go
View File

@ -12,7 +12,7 @@ import (
// implementation of GCM through the AEAD interface.
// See crypto/cipher/gcm.go.
type gcmAble interface {
NewGCM(size int) (cipher.AEAD, error)
NewGCM(nonceSize, tagSize int) (cipher.AEAD, error)
}
// cbcEncAble is implemented by cipher.Blocks that can provide an optimized

2
src/crypto/aes/modes_test.go
View File

@ -25,7 +25,7 @@ type testBlock struct{}
func (*testBlock) BlockSize() int { return 0 }
func (*testBlock) Encrypt(a, b []byte) {}
func (*testBlock) Decrypt(a, b []byte) {}
func (*testBlock) NewGCM(int) (cipher.AEAD, error) {
func (*testBlock) NewGCM(int, int) (cipher.AEAD, error) {
return &testAEAD{}, nil
}
func (*testBlock) NewCBCEncrypter([]byte) cipher.BlockMode {

52
src/crypto/cipher/gcm.go
View File

@ -48,7 +48,7 @@ type AEAD interface {
// implementation of GCM, like crypto/aes. NewGCM will check for this interface
// and return the specific AEAD if found.
type gcmAble interface {
NewGCM(int) (AEAD, error)
NewGCM(nonceSize, tagSize int) (AEAD, error)
}
// gcmFieldElement represents a value in GF(2¹²⁸). In order to reflect the GCM
@ -67,6 +67,7 @@ type gcmFieldElement struct {
type gcm struct {
cipher Block
nonceSize int
tagSize int
// productTable contains the first sixteen powers of the key, H.
// However, they are in bit reversed order. See NewGCMWithNonceSize.
productTable [16]gcmFieldElement
@ -79,7 +80,7 @@ type gcm struct {
// An exception is when the underlying Block was created by aes.NewCipher
// on systems with hardware support for AES. See the crypto/aes package documentation for details.
func NewGCM(cipher Block) (AEAD, error) {
return NewGCMWithNonceSize(cipher, gcmStandardNonceSize)
return NewGCMWithNonceAndTagSize(cipher, gcmStandardNonceSize, gcmTagSize)
}
// NewGCMWithNonceSize returns the given 128-bit, block cipher wrapped in Galois
@ -89,8 +90,24 @@ func NewGCM(cipher Block) (AEAD, error) {
// cryptosystem that uses non-standard nonce lengths. All other users should use
// NewGCM, which is faster and more resistant to misuse.
func NewGCMWithNonceSize(cipher Block, size int) (AEAD, error) {
return NewGCMWithNonceAndTagSize(cipher, size, gcmTagSize)
}
// NewGCMWithNonceAndTagSize returns the given 128-bit, block cipher wrapped in Galois
// Counter Mode, which accepts nonces of the given length and generates tags with the given length.
//
// Tag sizes between 12 and 16 bytes are allowed.
//
// Only use this function if you require compatibility with an existing
// cryptosystem that uses non-standard tag lengths. All other users should use
// NewGCM, which is more resistant to misuse.
func NewGCMWithNonceAndTagSize(cipher Block, nonceSize, tagSize int) (AEAD, error) {
if tagSize < gcmMinimumTagSize || tagSize > gcmBlockSize {
return nil, errors.New("cipher: incorrect tag size given to GCM")
}
if cipher, ok := cipher.(gcmAble); ok {
return cipher.NewGCM(size)
return cipher.NewGCM(nonceSize, tagSize)
}
if cipher.BlockSize() != gcmBlockSize {
@ -100,7 +117,7 @@ func NewGCMWithNonceSize(cipher Block, size int) (AEAD, error) {
var key [gcmBlockSize]byte
cipher.Encrypt(key[:], key[:])
g := &gcm{cipher: cipher, nonceSize: size}
g := &gcm{cipher: cipher, nonceSize: nonceSize, tagSize: tagSize}
// We precompute 16 multiples of |key|. However, when we do lookups
// into this table we'll be using bits from a field element and
@ -124,6 +141,7 @@ func NewGCMWithNonceSize(cipher Block, size int) (AEAD, error) {
const (
gcmBlockSize = 16
gcmTagSize = 16
gcmMinimumTagSize = 12 // NIST SP 800-38D recommends tags with 12 or more bytes.
gcmStandardNonceSize = 12
)
@ -131,8 +149,8 @@ func (g *gcm) NonceSize() int {
return g.nonceSize
}
func (*gcm) Overhead() int {
return gcmTagSize
func (g *gcm) Overhead() int {
return g.tagSize
}
func (g *gcm) Seal(dst, nonce, plaintext, data []byte) []byte {
@ -143,7 +161,7 @@ func (g *gcm) Seal(dst, nonce, plaintext, data []byte) []byte {
panic("cipher: message too large for GCM")
}
ret, out := sliceForAppend(dst, len(plaintext)+gcmTagSize)
ret, out := sliceForAppend(dst, len(plaintext)+g.tagSize)
var counter, tagMask [gcmBlockSize]byte
g.deriveCounter(&counter, nonce)
@ -152,7 +170,10 @@ func (g *gcm) Seal(dst, nonce, plaintext, data []byte) []byte {
gcmInc32(&counter)
g.counterCrypt(out, plaintext, &counter)
g.auth(out[len(plaintext):], out[:len(plaintext)], data, &tagMask)
var tag [gcmTagSize]byte
g.auth(tag[:], out[:len(plaintext)], data, &tagMask)
copy(out[len(plaintext):], tag[:])
return ret
}
@ -163,16 +184,21 @@ func (g *gcm) Open(dst, nonce, ciphertext, data []byte) ([]byte, error) {
if len(nonce) != g.nonceSize {
panic("cipher: incorrect nonce length given to GCM")
}
// Sanity check to prevent the authentication from always succeeding if an implementation
// leaves tagSize uninitialized, for example.
if g.tagSize < gcmMinimumTagSize {
panic("cipher: incorrect GCM tag size")
}
if len(ciphertext) < gcmTagSize {
if len(ciphertext) < g.tagSize {
return nil, errOpen
}
if uint64(len(ciphertext)) > ((1<<32)-2)*uint64(g.cipher.BlockSize())+gcmTagSize {
if uint64(len(ciphertext)) > ((1<<32)-2)*uint64(g.cipher.BlockSize())+uint64(g.tagSize) {
return nil, errOpen
}
tag := ciphertext[len(ciphertext)-gcmTagSize:]
ciphertext = ciphertext[:len(ciphertext)-gcmTagSize]
tag := ciphertext[len(ciphertext)-g.tagSize:]
ciphertext = ciphertext[:len(ciphertext)-g.tagSize]
var counter, tagMask [gcmBlockSize]byte
g.deriveCounter(&counter, nonce)
@ -185,7 +211,7 @@ func (g *gcm) Open(dst, nonce, ciphertext, data []byte) ([]byte, error) {
ret, out := sliceForAppend(dst, len(ciphertext))
if subtle.ConstantTimeCompare(expectedTag[:], tag) != 1 {
if subtle.ConstantTimeCompare(expectedTag[:g.tagSize], tag) != 1 {
// The AESNI code decrypts and authenticates concurrently, and
// so overwrites dst in the event of a tag mismatch. That
// behavior is mimicked here in order to be consistent across

46
src/crypto/cipher/gcm_test.go
View File

@ -188,6 +188,35 @@ var aesGCMTests = []struct {
"0feccdfae8ed65fa31a0858a1c466f79e8aa658c2f3ba93c3f92158b4e30955e1c62580450beff",
"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",
},
// These cases test non-standard tag sizes.
{
"89c54b0d3bc3c397d5039058c220685f",
"bc7f45c00868758d62d4bb4d",
"582670b0baf5540a3775b6615605bd05",
"48d16cda0337105a50e2ed76fd18e114",
"fc2d4c4eee2209ddbba6663c02765e6955e783b00156f5da0446e2970b877f",
},
{
"bad6049678bf75c9087b3e3ae7e72c13",
"a0a017b83a67d8f1b883e561",
"a1be93012f05a1958440f74a5311f4a1",
"f7c27b51d5367161dc2ff1e9e3edc6f2",
"36f032f7e3dc3275ca22aedcdc68436b99a2227f8bb69d45ea5d8842cd08",
},
{
"66a3c722ccf9709525650973ecc100a9",
"1621d42d3a6d42a2d2bf9494",
"61fa9dbbed2190fbc2ffabf5d2ea4ff8",
"d7a9b6523b8827068a6354a6d166c6b9",
"fef3b20f40e08a49637cc82f4c89b8603fd5c0132acfab97b5fff651c4",
},
{
"562ae8aadb8d23e0f271a99a7d1bd4d1",
"f7a5e2399413b89b6ad31aff",
"bbdc3504d803682aa08a773cde5f231a",
"2b9680b886b3efb7c6354b38c63b5373",
"e2b7e5ed5ff27fc8664148f5a628a46dcbf2015184fffb82f2651c36",
},
}
func TestAESGCM(t *testing.T) {
@ -201,7 +230,8 @@ func TestAESGCM(t *testing.T) {
nonce, _ := hex.DecodeString(test.nonce)
plaintext, _ := hex.DecodeString(test.plaintext)
ad, _ := hex.DecodeString(test.ad)
aesgcm, err := cipher.NewGCMWithNonceSize(aes, len(nonce))
tagSize := (len(test.result) - len(test.plaintext)) / 2
aesgcm, err := cipher.NewGCMWithNonceAndTagSize(aes, len(nonce), tagSize)
if err != nil {
t.Fatal(err)
}
@ -245,6 +275,20 @@ func TestAESGCM(t *testing.T) {
}
}
func TestGCMInvalidTagSize(t *testing.T) {
key, _ := hex.DecodeString("ab72c77b97cb5fe9a382d9fe81ffdbed")
nonce, _ := hex.DecodeString("54cc7dc2c37ec006bcc6d1db")
aes, _ := aes.NewCipher(key)
for _, tagSize := range []int{0, 1, aes.BlockSize() + 1} {
aesgcm, err := cipher.NewGCMWithNonceAndTagSize(aes, len(nonce), tagSize)
if aesgcm != nil || err == nil {
t.Fatalf("NewGCMWithNonceAndTagSize was successful with an invalid %d-byte tag size", tagSize)
}
}
}
func TestTagFailureOverwrite(t *testing.T) {
// The AESNI GCM code decrypts and authenticates concurrently and so
// overwrites the output buffer before checking the authentication tag.