diff --git a/src/main/java/com/sparrowwallet/drongo/Utils.java b/src/main/java/com/sparrowwallet/drongo/Utils.java
index 4d7136f..554c279 100644
--- a/src/main/java/com/sparrowwallet/drongo/Utils.java
+++ b/src/main/java/com/sparrowwallet/drongo/Utils.java
@@ -23,6 +23,7 @@ public class Utils {
 
     public static final String HEX_REGEX = "^[0-9A-Fa-f]+$";
     public static final String BASE64_REGEX = "^[0-9A-Za-z\\\\+=/]+$";
+    public static final String NUMERIC_REGEX = "^-?\\d+(\\.\\d+)?$";
 
     public static boolean isHex(String s)   {
         return s.matches(HEX_REGEX);
@@ -32,6 +33,10 @@ public class Utils {
         return s.matches(BASE64_REGEX);
     }
 
+    public static boolean isNumber(String s) {
+        return s.matches(NUMERIC_REGEX);
+    }
+
     public static boolean isUtf8(byte[] bytes) {
         try {
             CharsetDecoder decoder = StandardCharsets.UTF_8.newDecoder();
diff --git a/src/main/java/com/sparrowwallet/drongo/crypto/Pbkdf2KeyDeriver.java b/src/main/java/com/sparrowwallet/drongo/crypto/Pbkdf2KeyDeriver.java
index 578b27b..d3e57dc 100644
--- a/src/main/java/com/sparrowwallet/drongo/crypto/Pbkdf2KeyDeriver.java
+++ b/src/main/java/com/sparrowwallet/drongo/crypto/Pbkdf2KeyDeriver.java
@@ -7,25 +7,36 @@ import org.bouncycastle.crypto.params.KeyParameter;
 
 public class Pbkdf2KeyDeriver implements KeyDeriver, AsymmetricKeyDeriver {
     public static final int DEFAULT_ITERATION_COUNT = 1024;
+    public static final int DEFAULT_KEY_SIZE = 512;
 
     private final byte[] salt;
     private final int iterationCount;
+    private final int keySize;
 
     public static final Pbkdf2KeyDeriver DEFAULT_INSTANCE = new Pbkdf2KeyDeriver();
 
     public Pbkdf2KeyDeriver() {
         this.salt = new byte[0];
         this.iterationCount = DEFAULT_ITERATION_COUNT;
+        this.keySize = DEFAULT_KEY_SIZE;
     }
 
     public Pbkdf2KeyDeriver(byte[] salt) {
         this.salt = salt;
         this.iterationCount = DEFAULT_ITERATION_COUNT;
+        this.keySize = DEFAULT_KEY_SIZE;
     }
 
     public Pbkdf2KeyDeriver(byte[] salt, int iterationCount) {
         this.salt = salt;
         this.iterationCount = iterationCount;
+        this.keySize = DEFAULT_KEY_SIZE;
+    }
+
+    public Pbkdf2KeyDeriver(byte[] salt, int iterationCount, int keySize) {
+        this.salt = salt;
+        this.iterationCount = iterationCount;
+        this.keySize = keySize;
     }
 
     @Override
@@ -37,7 +48,7 @@ public class Pbkdf2KeyDeriver implements KeyDeriver, AsymmetricKeyDeriver {
     public Key deriveKey(CharSequence password) throws KeyCrypterException {
         PKCS5S2ParametersGenerator gen = new PKCS5S2ParametersGenerator(new SHA512Digest());
         gen.init(SecureString.toBytesUTF8(password), salt, iterationCount);
-        byte[] keyBytes = ((KeyParameter)gen.generateDerivedParameters(512)).getKey();
+        byte[] keyBytes = ((KeyParameter)gen.generateDerivedParameters(keySize)).getKey();
         return new Key(keyBytes, salt, getDeriverType());
     }