diff --git a/crypto/key_store_passphrase.go b/crypto/key_store_passphrase.go
index 2700b0f1c..19e77de91 100644
--- a/crypto/key_store_passphrase.go
+++ b/crypto/key_store_passphrase.go
@@ -61,12 +61,10 @@ type keyStorePassphrase struct {
 	keysDirPath string
 	scryptN     int
 	scryptP     int
-	scryptR     int
-	scryptDKLen int
 }
 
 func NewKeyStorePassphrase(path string, scryptN int, scryptP int) KeyStore {
-	return &keyStorePassphrase{path, scryptN, scryptP, scryptR, scryptDKLen}
+	return &keyStorePassphrase{path, scryptN, scryptP}
 }
 
 func (ks keyStorePassphrase) GenerateNewKey(rand io.Reader, auth string) (key *Key, err error) {
@@ -85,29 +83,38 @@ func (ks keyStorePassphrase) GetKeyAddresses() (addresses []common.Address, err
 	return getKeyAddresses(ks.keysDirPath)
 }
 
-func (ks keyStorePassphrase) StoreKey(key *Key, auth string) (err error) {
-	authArray := []byte(auth)
-	salt := randentropy.GetEntropyCSPRNG(32)
-	derivedKey, err := scrypt.Key(authArray, salt, ks.scryptN, ks.scryptR, ks.scryptP, ks.scryptDKLen)
+func (ks keyStorePassphrase) StoreKey(key *Key, auth string) error {
+	keyjson, err := EncryptKey(key, auth, ks.scryptN, ks.scryptP)
 	if err != nil {
 		return err
 	}
+	return writeKeyFile(key.Address, ks.keysDirPath, keyjson)
+}
+
+// EncryptKey encrypts a key using the specified scrypt parameters into a json
+// blob that can be decrypted later on.
+func EncryptKey(key *Key, auth string, scryptN, scryptP int) ([]byte, error) {
+	authArray := []byte(auth)
+	salt := randentropy.GetEntropyCSPRNG(32)
+	derivedKey, err := scrypt.Key(authArray, salt, scryptN, scryptR, scryptP, scryptDKLen)
+	if err != nil {
+		return nil, err
+	}
 	encryptKey := derivedKey[:16]
 	keyBytes := FromECDSA(key.PrivateKey)
 
 	iv := randentropy.GetEntropyCSPRNG(aes.BlockSize) // 16
 	cipherText, err := aesCTRXOR(encryptKey, keyBytes, iv)
 	if err != nil {
-		return err
+		return nil, err
 	}
-
 	mac := Keccak256(derivedKey[16:32], cipherText)
 
 	scryptParamsJSON := make(map[string]interface{}, 5)
-	scryptParamsJSON["n"] = ks.scryptN
-	scryptParamsJSON["r"] = ks.scryptR
-	scryptParamsJSON["p"] = ks.scryptP
-	scryptParamsJSON["dklen"] = ks.scryptDKLen
+	scryptParamsJSON["n"] = scryptN
+	scryptParamsJSON["r"] = scryptR
+	scryptParamsJSON["p"] = scryptP
+	scryptParamsJSON["dklen"] = scryptDKLen
 	scryptParamsJSON["salt"] = hex.EncodeToString(salt)
 
 	cipherParamsJSON := cipherparamsJSON{
@@ -128,12 +135,7 @@ func (ks keyStorePassphrase) StoreKey(key *Key, auth string) (err error) {
 		key.Id.String(),
 		version,
 	}
-	keyJSON, err := json.Marshal(encryptedKeyJSONV3)
-	if err != nil {
-		return err
-	}
-
-	return writeKeyFile(key.Address, ks.keysDirPath, keyJSON)
+	return json.Marshal(encryptedKeyJSONV3)
 }
 
 func (ks keyStorePassphrase) DeleteKey(keyAddr common.Address, auth string) error {
diff --git a/crypto/key_store_passphrase_test.go b/crypto/key_store_passphrase_test.go
new file mode 100644
index 000000000..bcdd58ad9
--- /dev/null
+++ b/crypto/key_store_passphrase_test.go
@@ -0,0 +1,51 @@
+// Copyright 2016 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package crypto
+
+import (
+	"testing"
+
+	"github.com/ethereum/go-ethereum/common"
+)
+
+// Tests that a json key file can be decrypted and encrypted in multiple rounds.
+func TestKeyEncryptDecrypt(t *testing.T) {
+	address := common.HexToAddress("f626acac23772cbe04dd578bee681b06bdefb9fa")
+	keyjson := []byte("{\"address\":\"f626acac23772cbe04dd578bee681b06bdefb9fa\",\"crypto\":{\"cipher\":\"aes-128-ctr\",\"ciphertext\":\"1bcf0ab9b14459795ce59f63e63255ffd84dc38d31614a5a78e37144d7e4a17f\",\"cipherparams\":{\"iv\":\"df4c7e225ee2d81adef522013e3fbe24\"},\"kdf\":\"scrypt\",\"kdfparams\":{\"dklen\":32,\"n\":262144,\"p\":1,\"r\":8,\"salt\":\"2909a99dd2bfa7079a4b40991773b1083f8512c0c55b9b63402ab0e3dc8db8b3\"},\"mac\":\"4ecf6a4ad92ae2c016cb7c44abade74799480c3303eb024661270dfefdbc7510\"},\"id\":\"b4718210-9a30-4883-b8a6-dbdd08bd0ceb\",\"version\":3}")
+	password := ""
+
+	// Do a few rounds of decryption and encryption
+	for i := 0; i < 3; i++ {
+		// Try a bad password first
+		if _, err := DecryptKey(keyjson, password+"bad"); err == nil {
+			t.Error("test %d: json key decrypted with bad password", i)
+		}
+		// Decrypt with the correct password
+		key, err := DecryptKey(keyjson, password)
+		if err != nil {
+			t.Errorf("test %d: json key failed to decrypt: %v", i, err)
+		}
+		if key.Address != address {
+			t.Errorf("test %d: key address mismatch: have %x, want %x", i, key.Address, address)
+		}
+		// Recrypt with a new password and start over
+		password += "new data appended"
+		if keyjson, err = EncryptKey(key, password, LightScryptN, LightScryptP); err != nil {
+			t.Errorf("test %d: failed to recrypt key %v", err)
+		}
+	}
+}