Merge pull request #4 from corverroos/corver/iteroption

Add cipher cost option

encrypt.go

@@ -28,14 +28,12 @@ import (
 
 const (
 	// Scrypt parameters
-	scryptN      = 262144
 	scryptr      = 8
 	scryptp      = 1
 	scryptKeyLen = 32
 
 	// PBKDF2 parameters
 	pbkdf2KeyLen = 32
-	pbkdf2c      = 262144
 	pbkdf2PRF    = "hmac-sha256"
 )
 
@@ -57,9 +55,9 @@ func (e *Encryptor) Encrypt(secret []byte, passphrase string) (map[string]interf
 	var err error
 	switch e.cipher {
 	case "scrypt":
-		decryptionKey, err = scrypt.Key(normedPassphrase, salt, scryptN, scryptr, scryptp, scryptKeyLen)
+		decryptionKey, err = scrypt.Key(normedPassphrase, salt, e.cost, scryptr, scryptp, scryptKeyLen)
 	case "pbkdf2":
-		decryptionKey = pbkdf2.Key(normedPassphrase, salt, pbkdf2c, pbkdf2KeyLen, sha256.New)
+		decryptionKey = pbkdf2.Key(normedPassphrase, salt, e.cost, pbkdf2KeyLen, sha256.New)
 	default:
 		return nil, fmt.Errorf("unknown cipher %q", e.cipher)
 	}
@@ -98,7 +96,7 @@ func (e *Encryptor) Encrypt(secret []byte, passphrase string) (map[string]interf
 			Function: "scrypt",
 			Params: &ksKDFParams{
 				DKLen: scryptKeyLen,
-				N:     scryptN,
+				N:     e.cost,
 				P:     scryptp,
 				R:     scryptr,
 				Salt:  hex.EncodeToString(salt),
@@ -110,7 +108,7 @@ func (e *Encryptor) Encrypt(secret []byte, passphrase string) (map[string]interf
 			Function: "pbkdf2",
 			Params: &ksKDFParams{
 				DKLen: pbkdf2KeyLen,
-				C:     pbkdf2c,
+				C:     e.cost,
 				PRF:   pbkdf2PRF,
 				Salt:  hex.EncodeToString(salt),
 			},

encrypt_test.go

@@ -26,6 +26,7 @@ func TestEncrypt(t *testing.T) {
 	tests := []struct {
 		name       string
 		cipher     string
+		costPower  uint
 		secret     []byte
 		passphrase string
 		err        error
@@ -57,8 +58,9 @@ func TestEncrypt(t *testing.T) {
 			err:        errors.New(`unknown cipher "unknown"`),
 		},
 		{
-			name:   "Good",
-			cipher: "scrypt",
+			name:      "Good",
+			cipher:    "pbkdf2",
+			costPower: 10,
 			secret: []byte{
 				0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
 				0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
@@ -67,11 +69,33 @@ func TestEncrypt(t *testing.T) {
 			},
 			passphrase: "wallet passphrase",
 		},
+		{
+			name:       "LowCostScrypt",
+			cipher:     "scrypt",
+			costPower:  10,
+			secret:     []byte(""),
+			passphrase: "",
+		},
+		{
+			name:       "LowCostPBKDF2",
+			cipher:     "pbkdf2",
+			costPower:  10,
+			secret:     []byte(""),
+			passphrase: "",
+		},
 	}
 
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
-			encryptor := keystorev4.New(keystorev4.WithCipher(test.cipher))
+			var options []keystorev4.Option
+			if test.cipher != "" {
+				options = append(options, keystorev4.WithCipher(test.cipher))
+			}
+			if test.costPower != 0 {
+				options = append(options, keystorev4.WithCost(t, test.costPower))
+			}
+
+			encryptor := keystorev4.New(options...)
 			_, err := encryptor.Encrypt(test.secret, test.passphrase)
 			if test.err != nil {
 				require.NotNil(t, err)
@@ -82,3 +106,9 @@ func TestEncrypt(t *testing.T) {
 		})
 	}
 }
+
+func TestWithCostPanic(t *testing.T) {
+	require.Panics(t, func() {
+		keystorev4.WithCost(nil, 1)
+	})
+}

encryptor.go

@@ -12,9 +12,12 @@
 
 package keystorev4
 
+import "testing"
+
 // Encryptor is an encryptor that follows the Ethereum keystore V4 specification.
 type Encryptor struct {
 	cipher string
+	cost   int
 }
 
 type ksKDFParams struct {
@@ -61,7 +64,8 @@ const (
 
 // options are the options for the keystore encryptor.
 type options struct {
-	cipher string
+	cipher    string
+	costPower uint
 }
 
 // Option gives options to New
@@ -82,19 +86,35 @@ func WithCipher(cipher string) Option {
 	})
 }
 
+// WithCost sets the cipher key cost for the encryptor to 2^power overriding
+// the default value of 18 (ie. 2^18=262144). Higher values increases the
+// cost of an exhaustive search but makes encoding and decoding proportionally slower.
+// This should only be in testing as it affects security. It panics if t is nil.
+func WithCost(t *testing.T, costPower uint) Option {
+	if t == nil {
+		panic("nil testing parameter")
+	}
+	return optionFunc(func(o *options) {
+		o.costPower = costPower
+	})
+}
+
 // New creates a new keystore V4 encryptor.
 // This takes the following options:
 // - cipher: the cipher to use when encrypting the secret, can be either "pbkdf2" (default) or "scrypt"
+// - costPower: the cipher key cost to use as power of 2, default is 18 (ie. 2^18).
 func New(opts ...Option) *Encryptor {
 	options := options{
-		cipher: "pbkdf2",
+		cipher:    "pbkdf2",
+		costPower: 18,
 	}
 	for _, o := range opts {
 		o.apply(&options)
 	}
 
 	return &Encryptor{
 		cipher: options.cipher,
+		cost:   1 << options.costPower,
 	}
 }
 

encryptor_test.go

@@ -34,6 +34,7 @@ func TestRoundTrip(t *testing.T) {
 		input      string
 		passphrase string
 		secret     []byte
+		options    []keystorev4.Option
 		err        error
 	}{
 		{
@@ -55,11 +56,24 @@ func TestRoundTrip(t *testing.T) {
 			passphrase: "𝔱𝔢𝔰𝔱𝔭𝔞𝔰𝔰𝔴𝔬𝔯𝔡🔑",
 			secret:     []byte{0x00, 0x00, 0x00, 0x00, 0x00, 0x19, 0xd6, 0x68, 0x9c, 0x08, 0x5a, 0xe1, 0x65, 0x83, 0x1e, 0x93, 0x4f, 0xf7, 0x63, 0xae, 0x46, 0xa2, 0xa6, 0xc1, 0x72, 0xb3, 0xf1, 0xb6, 0x0a, 0x8c, 0xe2, 0x6f},
 		},
+		{
+			name:       "LowCostScrypt",
+			input:      `{"checksum":{"function":"sha256","message":"e4c3c7171f8ff54478868dbf1648dac50c6f38dafe5d9c8dd9f312b812f7fc44","params":{}},"cipher":{"function":"aes-128-ctr","message":"a71e9211932429462d3f6b032a800452651d0cf4517cc0f28c65be57df78f675","params":{"iv":"f68ce93072d0b6c6ca8afbc9b002cd89"}},"kdf":{"function":"scrypt","message":"","params":{"dklen":32,"n":1024,"p":1,"r":8,"salt":"316bd15fbca6d44e543f91762b66a29d2e3f590a9f7a42b9eff1dec48df0075f"}}}`,
+			passphrase: "𝔱𝔢𝔰𝔱𝔭𝔞𝔰𝔰𝔴𝔬𝔯𝔡🔑",
+			secret:     []byte{0x00, 0x00, 0x00, 0x00, 0x00, 0x19, 0xd6, 0x68, 0x9c, 0x08, 0x5a, 0xe1, 0x65, 0x83, 0x1e, 0x93, 0x4f, 0xf7, 0x63, 0xae, 0x46, 0xa2, 0xa6, 0xc1, 0x72, 0xb3, 0xf1, 0xb6, 0x0a, 0x8c, 0xe2, 0x6f},
+			options:    []keystorev4.Option{keystorev4.WithCipher("scrypt"), keystorev4.WithCost(t, 10)},
+		}, {
+			name:       "LowCostPBKDF2",
+			input:      `{"checksum":{"function":"sha256","message":"57dbef6061fe5832064da342e92cac95917ff6d928d278919e3ddb7ae89c05c7","params":{}},"cipher":{"function":"aes-128-ctr","message":"cfe1132d3f0fe4f59d38f5eef01b80be32517448fa65dd0476171324cc3ab5fc","params":{"iv":"5975ccd92bc36290f082f134ec4c52bd"}},"kdf":{"function":"pbkdf2","message":"","params":{"c":1024,"dklen":32,"prf":"hmac-sha256","salt":"700ca70794d861f8f35d733e83c67431c893aa8e83b0dc43b6abd62edf9df0d1"}}}`,
+			passphrase: "𝔱𝔢𝔰𝔱𝔭𝔞𝔰𝔰𝔴𝔬𝔯𝔡🔑",
+			secret:     []byte{0x00, 0x00, 0x00, 0x00, 0x00, 0x19, 0xd6, 0x68, 0x9c, 0x08, 0x5a, 0xe1, 0x65, 0x83, 0x1e, 0x93, 0x4f, 0xf7, 0x63, 0xae, 0x46, 0xa2, 0xa6, 0xc1, 0x72, 0xb3, 0xf1, 0xb6, 0x0a, 0x8c, 0xe2, 0x6f},
+			options:    []keystorev4.Option{keystorev4.WithCost(t, 10)},
+		},
 	}
 
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
-			encryptor := keystorev4.New()
+			encryptor := keystorev4.New(test.options...)
 			input := make(map[string]interface{})
 			err := json.Unmarshal([]byte(test.input), &input)
 			require.Nil(t, err)