Rework v1.local (#9)

common.go

@@ -2,6 +2,7 @@ package paseto
 
 import (
 	"bytes"
+	"crypto/subtle"
 	"encoding/base64"
 	"encoding/binary"
 	"encoding/json"
@@ -50,7 +51,7 @@ func fromBytes(data []byte, x any) error {
 		*f = append(*f, data...)
 	default:
 		if err := json.Unmarshal(data, x); err != nil {
-			return fmt.Errorf("%v: %w", err, ErrDataUnmarshal)
+			return fmt.Errorf("%w: %v", ErrDataUnmarshal, err)
 		}
 	}
 	return nil
@@ -89,7 +90,7 @@ func splitToken(token, header string) ([]byte, []byte, error) {
 	return payload, footer, nil
 }
 
-func buildToken(header string, body, footer []byte) string {
+func buildToken(header, body, footer []byte) string {
 	size := len(header) + b64EncodedLen(len(body))
 	if len(footer) > 0 {
 		size += 1 + b64EncodedLen(len(footer))
@@ -124,3 +125,7 @@ func b64Encode(dst, src []byte) {
 func b64EncodedLen(n int) int {
 	return base64.RawURLEncoding.EncodedLen(n)
 }
+
+func constTimeEq(x, y int32) bool {
+	return subtle.ConstantTimeEq(x, y) == 1
+}

common_test.go

@@ -43,7 +43,7 @@ func BenchmarkPAE(b *testing.B) {
 	var footerBytes []byte
 
 	pieces := [][]byte{
-		[]byte(v1LocHeader),
+		[]byte(v1locHeader),
 		nonce[:],
 		encryptedPayload[:],
 		footerBytes,

v1loc.go

@@ -6,27 +6,23 @@ import (
 	"crypto/hmac"
 	"crypto/rand"
 	"crypto/sha512"
+	"errors"
 	"fmt"
 	"io"
+	"strings"
 
 	"golang.org/x/crypto/hkdf"
 )
 
 const (
-	v1LocHeader    = "v1.local."
-	v1LocNonceSize = 32
-	v1LocNonceHalf = v1LocNonceSize / 2
-	v1LocMacSize   = 48 // const for crypty.SHA384.Size()
+	v1locHeader = "v1.local."
+	v1locKey    = 32
+	v1locNonce  = 32
+	v1locNonceH = v1locNonce / 2
+	v1locMac    = 48 // const for crypto.SHA384.Size()
 )
 
 func V1Encrypt(key []byte, payload, footer any, randBytes []byte) (string, error) {
-	if randBytes == nil {
-		randBytes = make([]byte, v1LocNonceSize)
-		if _, err := io.ReadFull(rand.Reader, randBytes); err != nil {
-			return "", fmt.Errorf("read from crypto/rand.Reader: %w", err)
-		}
-	}
-
 	payloadBytes, err := toBytes(payload)
 	if err != nil {
 		return "", fmt.Errorf("encode payload: %w", err)
@@ -37,76 +33,124 @@ func V1Encrypt(key []byte, payload, footer any, randBytes []byte) (string, error
 		return "", fmt.Errorf("encode footer: %w", err)
 	}
 
-	macN := hmac.New(sha512.New384, randBytes)
-	if _, err := macN.Write(payloadBytes); err != nil {
-		return "", fmt.Errorf("hash payload: %w", err)
+	m := payloadBytes
+	k := key
+	f := footerBytes
+
+	// step 1.
+	if !constTimeEq(int32(len(k)), v1locKey) {
+		return "", errors.New("bad key")
 	}
-	nonce := macN.Sum(nil)[:v1LocNonceSize]
 
-	encKey, authKey, err := v1locSplitKey(key, nonce[:v1LocNonceHalf])
+	// step 2.
+	h := []byte(v1locHeader)
+
+	// step 3.
+	b := randBytes
+	if b == nil {
+		b = make([]byte, v1locNonce)
+		if _, err := io.ReadFull(rand.Reader, b); err != nil {
+			return "", fmt.Errorf("read from crypto/rand.Reader: %w", err)
+		}
+	}
+
+	// step 4.
+	hash := hmac.New(sha512.New384, b)
+	hash.Write(m)
+	n := hash.Sum(nil)[:v1locNonce]
+
+	// step 5.
+	ek, ak, err := v1locSplitKey(k, n[:v1locNonceH])
 	if err != nil {
 		return "", fmt.Errorf("create enc and auth keys: %w", err)
 	}
 
-	block, err := aes.NewCipher(encKey)
+	// step 6.
+	block, err := aes.NewCipher(ek)
 	if err != nil {
 		return "", fmt.Errorf("create aes cipher: %w", err)
 	}
+	c := make([]byte, len(m))
+	ciph := cipher.NewCTR(block, n[v1locNonceH:])
+	ciph.XORKeyStream(c, m)
 
-	encryptedPayload := make([]byte, len(payloadBytes))
-	cipher.NewCTR(block, nonce[v1LocNonceHalf:]).
-		XORKeyStream(encryptedPayload, payloadBytes)
+	// step 7.
+	preAuth := pae(h, n, c, f)
 
-	h := hmac.New(sha512.New384, authKey)
-	if _, err := h.Write(pae([]byte(v1LocHeader), nonce, encryptedPayload, footerBytes)); err != nil {
-		return "", fmt.Errorf("create signature: %w", err)
-	}
-	mac := h.Sum(nil)
+	// step 8.
+	hasher := hmac.New(sha512.New384, ak)
+	hasher.Write(preAuth)
+	t := hasher.Sum(nil)
 
-	body := make([]byte, 0, len(nonce)+len(encryptedPayload)+len(mac))
-	body = append(body, nonce...)
-	body = append(body, encryptedPayload...)
-	body = append(body, mac...)
+	// step 9.
+	body := make([]byte, 0, len(n)+len(c)+len(t))
+	body = append(body, n...)
+	body = append(body, c...)
+	body = append(body, t...)
 
-	return buildToken(v1LocHeader, body, footerBytes), nil
+	return buildToken(h, body, f), nil
 }
 
 func V1Decrypt(token string, key []byte, payload, footer any) error {
-	data, footerBytes, err := splitToken(token, v1LocHeader)
+	// step 0.
+	k := key
+
+	// step 1.
+	if !constTimeEq(int32(len(k)), v1locKey) {
+		return errors.New("bad key")
+	}
+
+	// step 2.
+	// TODO: ?
+
+	// step 3.
+	if !strings.HasPrefix(token, v1locHeader) {
+		return ErrIncorrectTokenFormat
+	}
+	h := []byte(v1locHeader)
+
+	// step 4.
+	data, footerBytes, err := splitToken(token, v1locHeader)
 	if err != nil {
 		return fmt.Errorf("decode token: %w", err)
 	}
-	if len(data) < v1LocNonceSize+v1LocMacSize {
+	if len(data) < v1locNonce+v1locMac {
 		return ErrIncorrectTokenFormat
 	}
+	f := footerBytes
 
-	pivot := len(data) - v1LocMacSize
-	nonce := data[:v1LocNonceSize]
-	encryptedPayload, mac := data[v1LocNonceSize:pivot], data[pivot:]
+	pivot := len(data) - v1locMac
+	n := data[:v1locNonce]
+	c, t := data[v1locNonce:pivot], data[pivot:]
 
-	encKey, authKey, err := v1locSplitKey(key, nonce[:v1LocNonceHalf])
+	// step 5.
+	ek, ak, err := v1locSplitKey(k, n[:v1locNonceH])
 	if err != nil {
 		return fmt.Errorf("create enc and auth keys: %w", err)
 	}
 
-	body := pae([]byte(v1LocHeader), nonce, encryptedPayload, footerBytes)
-	h := hmac.New(sha512.New384, authKey)
-	if _, err := h.Write(body); err != nil {
-		return fmt.Errorf("create signature: %w", err)
-	}
+	// step 6.
+	preAuth := pae(h, n, c, f)
+
+	// step 7.
+	hasher := hmac.New(sha512.New384, ak)
+	hasher.Write(preAuth)
+	t2 := hasher.Sum(nil)
 
-	if !hmac.Equal(h.Sum(nil), mac) {
+	// step 8.
+	if !hmac.Equal(t2, t) {
 		return ErrInvalidTokenAuth
 	}
 
-	block, err := aes.NewCipher(encKey)
+	// step 9.
+	block, err := aes.NewCipher(ek)
 	if err != nil {
 		return fmt.Errorf("create aes cipher: %w", err)
 	}
 
-	decryptedPayload := make([]byte, len(encryptedPayload))
-	cipher.NewCTR(block, nonce[v1LocNonceHalf:]).
-		XORKeyStream(decryptedPayload, encryptedPayload)
+	decryptedPayload := make([]byte, len(c))
+	ciph := cipher.NewCTR(block, n[v1locNonceH:])
+	ciph.XORKeyStream(decryptedPayload, c)
 
 	if payload != nil {
 		if err := fromBytes(decryptedPayload, payload); err != nil {
@@ -126,14 +170,14 @@ func v1locSplitKey(key, salt []byte) ([]byte, []byte, error) {
 	eReader := hkdf.New(sha512.New384, key, salt, []byte("paseto-encryption-key"))
 	aReader := hkdf.New(sha512.New384, key, salt, []byte("paseto-auth-key-for-aead"))
 
-	encKey := make([]byte, 32)
-	authKey := make([]byte, 32)
+	ek := make([]byte, 32)
+	ak := make([]byte, 32)
 
-	if _, err := io.ReadFull(eReader, encKey); err != nil {
+	if _, err := io.ReadFull(eReader, ek); err != nil {
 		return nil, nil, err
 	}
-	if _, err := io.ReadFull(aReader, authKey); err != nil {
+	if _, err := io.ReadFull(aReader, ak); err != nil {
 		return nil, nil, err
 	}
-	return encKey, authKey, nil
+	return ek, ak, nil
 }

v1loc_test.go

@@ -10,7 +10,7 @@ func TestV1Loc_Encrypt(t *testing.T) {
 	testCases := loadGoldenFile("testdata/v1.json")
 
 	for _, tc := range testCases.Tests {
-		if tc.Key == "" || !strings.HasPrefix(tc.Token, v1LocHeader) {
+		if tc.Key == "" || !strings.HasPrefix(tc.Token, v1locHeader) {
 			continue
 		}
 
@@ -30,8 +30,8 @@ func TestV1Loc_Encrypt(t *testing.T) {
 func TestV1Loc_Decrypt(t *testing.T) {
 	testCases := loadGoldenFile("testdata/v1.json")
 
-	for _, tc := range testCases.Tests[:] {
-		if tc.Key == "" || !strings.HasPrefix(tc.Token, v1LocHeader) {
+	for _, tc := range testCases.Tests {
+		if tc.Key == "" || !strings.HasPrefix(tc.Token, v1locHeader) {
 			continue
 		}
 

v2loc.go

@@ -56,7 +56,7 @@ func V2Encrypt(key []byte, payload, footer any, randBytes []byte) (string, error
 	)
 	body := append(nonce, encryptedPayload...)
 
-	return buildToken(v2LocHeader, body, footerBytes), nil
+	return buildToken([]byte(v2LocHeader), body, footerBytes), nil
 }
 
 func V2Decrypt(token string, key []byte, payload, footer any) error {