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Expose CBC via cipher.AEAD
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This is rather an abuse of the cipher.AEAD interface as the name
and description both indicate it provides authenticated encryption,
which is not the case for CBC. The risk of using it in a context
where authentication is required is mitigated only by documentation.

re #6
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Richard Kettlewell authored and Richard Kettlewell committed Oct 3, 2018
1 parent 15ff8ec commit 851d862
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Showing 2 changed files with 117 additions and 29 deletions.
120 changes: 96 additions & 24 deletions symmetric.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -24,12 +24,21 @@ package crypto11
import (
"context"
"crypto/cipher"
"errors"
"fmt"
"github.com/miekg/pkcs11"
"github.com/youtube/vitess/go/pools"
"runtime"
)

const (
// PaddingNone represents a block cipher with no padding.
PaddingNone = iota

// PaddingPKCS represents a block cipher used with PKCS#7 padding.
PaddingPKCS
)

// SymmetricGenParams holds a consistent (key type, mechanism) key generation pair.
type SymmetricGenParams struct {
// Key type (CKK_...)
Expand Down Expand Up @@ -60,6 +69,9 @@ type SymmetricCipher struct {
// CBC mechanism (CKM_..._CBC)
CBCMech uint

// CBC mechanism with PKCS#7 padding (CKM_..._CBC)
CBCPKCSMech uint

// GCM mechanism (CKM_..._GCM)
GCMMech uint
}
Expand All @@ -73,12 +85,13 @@ var CipherAES = SymmetricCipher{
GenMech: pkcs11.CKM_AES_KEY_GEN,
},
},
BlockSize: 16,
Encrypt: true,
MAC: false,
ECBMech: pkcs11.CKM_AES_ECB,
CBCMech: pkcs11.CKM_AES_CBC,
GCMMech: pkcs11.CKM_AES_GCM,
BlockSize: 16,
Encrypt: true,
MAC: false,
ECBMech: pkcs11.CKM_AES_ECB,
CBCMech: pkcs11.CKM_AES_CBC,
CBCPKCSMech: pkcs11.CKM_AES_CBC_PAD,
GCMMech: pkcs11.CKM_AES_GCM,
}

// CipherDES3 describes the three-key triple-DES cipher. Use this with the
Expand All @@ -90,12 +103,13 @@ var CipherDES3 = SymmetricCipher{
GenMech: pkcs11.CKM_DES3_KEY_GEN,
},
},
BlockSize: 8,
Encrypt: true,
MAC: false,
ECBMech: pkcs11.CKM_DES3_ECB,
CBCMech: pkcs11.CKM_DES3_CBC,
GCMMech: 0,
BlockSize: 8,
Encrypt: true,
MAC: false,
ECBMech: pkcs11.CKM_DES3_ECB,
CBCMech: pkcs11.CKM_DES3_CBC,
CBCPKCSMech: pkcs11.CKM_DES3_CBC_PAD,
GCMMech: 0,
}

// CipherGeneric describes the CKK_GENERIC_SECRET key type. Use this with the
Expand Down Expand Up @@ -386,8 +400,14 @@ func (key *PKCS11SecretKey) Encrypt(dst, src []byte) {

// cipher.AEAD ----------------------------------------------------------

type gcmAead struct {
type genericAead struct {
key *PKCS11SecretKey

overhead int

nonceSize int

makeMech func(nonce []byte, additionalData []byte) ([]*pkcs11.Mechanism, error)
}

// NewGCM returns a given cipher wrapped in Galois Counter Mode, with the standard
Expand All @@ -400,27 +420,75 @@ func (key *PKCS11SecretKey) NewGCM() (g cipher.AEAD, err error) {
err = fmt.Errorf("GCM not implemented for key type %#x", key.Cipher.GenParams[0].KeyType)
return
}
g = gcmAead{key}
g = genericAead{
key: key,
overhead: 16,
nonceSize: 12,
makeMech: func(nonce []byte, additionalData []byte) (mech []*pkcs11.Mechanism, error error) {
params := pkcs11.NewGCMParams(nonce, additionalData, 16)
mech = []*pkcs11.Mechanism{pkcs11.NewMechanism(key.Cipher.GCMMech, params)}
return
},
}
return
}

func (g gcmAead) NonceSize() int {
return 12
// NewCBC returns a given cipher wrapped in CBC mode.
//
// Despite the cipher.AEAD return type, there is no support for additional data and no authentication.
// This method exists to provide a convenient way to do bulk (possibly padded) CBC encryption.
// Think carefully before passing the cipher.AEAD to any consumer that expects authentication.
func (key *PKCS11SecretKey) NewCBC(paddingMode int) (g cipher.AEAD, err error) {
g = genericAead{
key: key,
overhead: 0,
nonceSize: key.BlockSize(),
makeMech: func(nonce []byte, additionalData []byte) (mech []*pkcs11.Mechanism, error error) {
if len(additionalData) > 0 {
err = errors.New("additional data not supported for CBC mode")
}
var pkcsMech uint
switch paddingMode {
case PaddingNone:
pkcsMech = key.Cipher.CBCMech
case PaddingPKCS:
pkcsMech = key.Cipher.CBCPKCSMech
default:
err = errors.New("unrecognized padding mode")
return
}
if pkcsMech == 0 {
err = errors.New("unsupported padding mode")
return
}
mech = []*pkcs11.Mechanism{pkcs11.NewMechanism(pkcsMech, nonce)}
return
},
}
return
}

func (g gcmAead) Overhead() int {
return 16
func (g genericAead) NonceSize() int {
return g.nonceSize
}

func (g gcmAead) Seal(dst, nonce, plaintext, additionalData []byte) []byte {
func (g genericAead) Overhead() int {
return g.overhead
}

func (g genericAead) Seal(dst, nonce, plaintext, additionalData []byte) []byte {
var result []byte
if err := withSession(g.key.Slot, func(session *PKCS11Session) (err error) {
params := pkcs11.NewGCMParams(nonce, additionalData, 16)
mech := []*pkcs11.Mechanism{pkcs11.NewMechanism(g.key.Cipher.GCMMech, params)}
var mech []*pkcs11.Mechanism
if mech, err = g.makeMech(nonce, additionalData); err != nil {
return
}
if err = session.Ctx.EncryptInit(session.Handle, mech, g.key.Handle); err != nil {
err = fmt.Errorf("C_EncryptInit: %v", err)
return
}
if result, err = session.Ctx.Encrypt(session.Handle, plaintext); err != nil {
err = fmt.Errorf("C_Encrypt: %v", err)
return
}
return
Expand All @@ -432,15 +500,19 @@ func (g gcmAead) Seal(dst, nonce, plaintext, additionalData []byte) []byte {
return dst
}

func (g gcmAead) Open(dst, nonce, ciphertext, additionalData []byte) ([]byte, error) {
func (g genericAead) Open(dst, nonce, ciphertext, additionalData []byte) ([]byte, error) {
var result []byte
if err := withSession(g.key.Slot, func(session *PKCS11Session) (err error) {
params := pkcs11.NewGCMParams(nonce, additionalData, 16)
mech := []*pkcs11.Mechanism{pkcs11.NewMechanism(g.key.Cipher.GCMMech, params)}
var mech []*pkcs11.Mechanism
if mech, err = g.makeMech(nonce, additionalData); err != nil {
return
}
if err = session.Ctx.DecryptInit(session.Handle, mech, g.key.Handle); err != nil {
err = fmt.Errorf("C_DecryptInit: %v", err)
return
}
if result, err = session.Ctx.Decrypt(session.Handle, ciphertext); err != nil {
err = fmt.Errorf("C_Decrypt: %v", err)
return
}
return
Expand Down
26 changes: 21 additions & 5 deletions symmetric_test.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -102,14 +102,30 @@ func testHardSymmetric(t *testing.T, keytype int, bits int) {
// See discussion at BlockModeCloser.
runtime.GC()
})
t.Run("CBCSealOpen", func(t *testing.T) {
aead, err := key2.NewCBC(PaddingNone)
if err != nil {
t.Errorf("cipher.NewCBC: %v", err)
return
}
testAEADMode(t, aead, 128, 0)
})
t.Run("CBCPKCSSealOpen", func(t *testing.T) {
aead, err := key2.NewCBC(PaddingPKCS)
if err != nil {
t.Errorf("cipher.NewCBC: %v", err)
return
}
testAEADMode(t, aead, 127, 0)
})
if bits == 128 {
t.Run("GCMSoft", func(t *testing.T) {
aead, err := cipher.NewGCM(key2)
if err != nil {
t.Errorf("cipher.NewGCM: %v", err)
return
}
testAEADMode(t, aead)
testAEADMode(t, aead, 127, 129)
})
t.Run("GCMHard", func(t *testing.T) {
var info pkcs11.Info
Expand All @@ -125,7 +141,7 @@ func testHardSymmetric(t *testing.T, keytype int, bits int) {
t.Errorf("key2.NewGCM: %v", err)
return
}
testAEADMode(t, aead)
testAEADMode(t, aead, 127, 129)
})
// TODO check that hard/soft is consistent!
}
Expand Down Expand Up @@ -222,13 +238,13 @@ func testSymmetricMode(t *testing.T, encrypt cipher.BlockMode, decrypt cipher.Bl
}
}

func testAEADMode(t *testing.T, aead cipher.AEAD) {
func testAEADMode(t *testing.T, aead cipher.AEAD, ptlen int, adlen int) {
nonce := make([]byte, aead.NonceSize())
plaintext := make([]byte, 127)
plaintext := make([]byte, ptlen)
for i := 0; i < len(plaintext); i++ {
plaintext[i] = byte(i)
}
additionalData := make([]byte, 129)
additionalData := make([]byte, adlen)
for i := 0; i < len(additionalData); i++ {
additionalData[i] = byte(i + 16)
}
Expand Down

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