use charsequence and securestring instead of string

src/main/java/com/sparrowwallet/drongo/SecureString.java

@@ -0,0 +1,100 @@
+package com.sparrowwallet.drongo;
+
+import java.security.SecureRandom;
+import java.util.Arrays;
+
+/**
+ * This is not a string but a CharSequence that can be cleared of its memory.
+ * Important for handling passwords. Represents text that should be kept
+ * confidential, such as by deleting it from computer memory when no longer
+ * needed or garbaged collected.
+ */
+public class SecureString implements CharSequence {
+
+    private final int[] chars;
+    private final int[] pad;
+
+    public SecureString(final CharSequence original) {
+        this(0, original.length(), original);
+    }
+
+    public SecureString(final int start, final int end, final CharSequence original) {
+        final int length = end - start;
+        pad = new int[length];
+        chars = new int[length];
+        scramble(start, length, original);
+    }
+
+    @Override
+    public char charAt(final int i) {
+        return (char) (pad[i] ^ chars[i]);
+    }
+
+    @Override
+    public int length() {
+        return chars.length;
+    }
+
+    @Override
+    public CharSequence subSequence(final int start, final int end) {
+        return new SecureString(start, end, this);
+    }
+
+    /**
+     * Convert array back to String but not using toString(). See toString() docs
+     * below.
+     */
+    public String asString() {
+        final char[] value = new char[chars.length];
+        for (int i = 0; i < value.length; i++) {
+            value[i] = charAt(i);
+        }
+        return new String(value);
+    }
+
+    /**
+     * Manually clear the underlying array holding the characters
+     */
+    public void clear() {
+        Arrays.fill(chars, '0');
+        Arrays.fill(pad, 0);
+    }
+
+    /**
+     * Protect against using this class in log statements.
+     * <p>
+     * {@inheritDoc}
+     */
+    @Override
+    public String toString() {
+        return "Secure:XXXXX";
+    }
+
+    /**
+     * Called by garbage collector.
+     * <p>
+     * {@inheritDoc}
+     */
+    @SuppressWarnings("deprecation")
+    @Override
+    public void finalize() throws Throwable {
+        clear();
+        super.finalize();
+    }
+
+    /**
+     * Randomly pad the characters to not store the real character in memory.
+     *
+     * @param start start of the {@code CharSequence}
+     * @param length length of the {@code CharSequence}
+     * @param characters the {@code CharSequence} to scramble
+     */
+    private void scramble(final int start, final int length, final CharSequence characters) {
+        final SecureRandom random = new SecureRandom();
+        for (int i = start; i < length; i++) {
+            final char charAt = characters.charAt(i);
+            pad[i] = random.nextInt();
+            chars[i] = pad[i] ^ charAt;
+        }
+    }
+}

src/main/java/com/sparrowwallet/drongo/Utils.java

@@ -5,7 +5,6 @@ import com.sparrowwallet.drongo.protocol.ProtocolException;
 import com.sparrowwallet.drongo.protocol.Ripemd160;
 import com.sparrowwallet.drongo.protocol.Sha256Hash;
 import org.bouncycastle.crypto.digests.SHA512Digest;
-import org.bouncycastle.crypto.generators.PKCS5S2ParametersGenerator;
 import org.bouncycastle.crypto.macs.HMac;
 import org.bouncycastle.crypto.params.KeyParameter;
 
@@ -13,6 +12,10 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.math.BigInteger;
+import java.nio.Buffer;
+import java.nio.ByteBuffer;
+import java.nio.CharBuffer;
+import java.nio.charset.StandardCharsets;
 import java.util.*;
 
 public class Utils {
@@ -280,4 +283,40 @@ public class Utils {
         hmacSha512.doFinal(out, 0);
         return out;
     }
+
+    public static byte[] toBytesUTF8(CharSequence charSequence) {
+        CharBuffer charBuffer = CharBuffer.wrap(charSequence);
+        ByteBuffer byteBuffer = StandardCharsets.UTF_8.encode(charBuffer);
+        byte[] bytes = Arrays.copyOfRange(byteBuffer.array(), byteBuffer.position(), byteBuffer.limit());
+        Arrays.fill(byteBuffer.array(), (byte)0); // clear sensitive data
+        return bytes;
+    }
+
+    public static SecureString fromBytesUTF8(byte[] bytes) {
+        ByteBuffer byteBuffer = ByteBuffer.wrap(bytes);
+        CharBuffer charBuffer = StandardCharsets.UTF_8.decode(byteBuffer);
+        SecureString secureString = new SecureString(charBuffer);
+        Arrays.fill(charBuffer.array(), (char)0);
+        return secureString;
+    }
+
+    public static byte[] toBytesUTF16(CharSequence charSequence) {
+        byte[] byteArray = new byte[charSequence.length() << 1];
+        for(int i = 0; i < charSequence.length(); i++) {
+            int bytePosition = i << 1;
+            byteArray[bytePosition] = (byte) ((charSequence.charAt(i)&0xFF00)>>8);
+            byteArray[bytePosition + 1] = (byte) (charSequence.charAt(i)&0x00FF);
+        }
+        return byteArray;
+    }
+
+    public static boolean isValidUTF16(CharSequence charSequence) {
+        for (int i = 0; i < charSequence.length(); i++) {
+            if (Character.isLowSurrogate(charSequence.charAt(i)) && (i == 0 || !Character.isHighSurrogate(charSequence.charAt(i - 1)))
+                    || Character.isHighSurrogate(charSequence.charAt(i)) && (i == charSequence.length() -1 || !Character.isLowSurrogate(charSequence.charAt(i + 1)))) {
+                return false;
+            }
+        }
+        return true;
+    }
 }

src/main/java/com/sparrowwallet/drongo/crypto/Argon2KeyDeriver.java

@@ -1,9 +1,9 @@
 package com.sparrowwallet.drongo.crypto;
 
+import com.sparrowwallet.drongo.Utils;
 import de.mkammerer.argon2.Argon2Advanced;
 import de.mkammerer.argon2.Argon2Factory;
 
-import java.nio.charset.StandardCharsets;
 import java.security.SecureRandom;
 
 public class Argon2KeyDeriver implements KeyDeriver, AsymmetricKeyDeriver {
@@ -40,14 +40,14 @@ public class Argon2KeyDeriver implements KeyDeriver, AsymmetricKeyDeriver {
     }
 
     @Override
-    public Key deriveKey(String password) throws KeyCrypterException {
+    public Key deriveKey(CharSequence password) throws KeyCrypterException {
         Argon2Advanced argon2 = Argon2Factory.createAdvanced(Argon2Factory.Argon2Types.ARGON2id, argon2Parameters.saltLength, argon2Parameters.hashLength);
-        byte[] hash = argon2.rawHash(argon2Parameters.iterations, argon2Parameters.memory, argon2Parameters.parallelism, password.getBytes(StandardCharsets.UTF_8), salt);
+        byte[] hash = argon2.rawHash(argon2Parameters.iterations, argon2Parameters.memory, argon2Parameters.parallelism, Utils.toBytesUTF8(password), salt);
         return new Key(hash, salt, getDeriverType());
     }
 
     @Override
-    public ECKey deriveECKey(String password) throws KeyCrypterException {
+    public ECKey deriveECKey(CharSequence password) throws KeyCrypterException {
         Key key = deriveKey(password);
         return ECKey.fromPrivate(key.getKeyBytes());
     }

src/main/java/com/sparrowwallet/drongo/crypto/AsymmetricKeyDeriver.java

@@ -7,7 +7,7 @@ public interface AsymmetricKeyDeriver {
      * @return ECKey The ECKey to use for encrypting and decrypting
      * @throws KeyCrypterException
      */
-    ECKey deriveECKey(String password) throws KeyCrypterException;
+    ECKey deriveECKey(CharSequence password) throws KeyCrypterException;
 
     byte[] getSalt();
 }

src/main/java/com/sparrowwallet/drongo/crypto/DoubleSha256KeyDeriver.java

@@ -1,5 +1,6 @@
 package com.sparrowwallet.drongo.crypto;
 
+import com.sparrowwallet.drongo.Utils;
 import com.sparrowwallet.drongo.protocol.Sha256Hash;
 
 import java.nio.charset.StandardCharsets;
@@ -7,8 +8,9 @@ import java.nio.charset.StandardCharsets;
 public class DoubleSha256KeyDeriver implements KeyDeriver {
 
     @Override
-    public Key deriveKey(String password) throws KeyCrypterException {
+    public Key deriveKey(CharSequence password) throws KeyCrypterException {
-        byte[] sha256 = Sha256Hash.hash(password.getBytes(StandardCharsets.UTF_8));
+        byte[] passwordBytes = Utils.toBytesUTF8(password);
+        byte[] sha256 = Sha256Hash.hash(passwordBytes);
         byte[] doubleSha256 = Sha256Hash.hash(sha256);
         return new Key(doubleSha256, null, getDeriverType());
     }

src/main/java/com/sparrowwallet/drongo/crypto/EncryptionType.java

@@ -1,5 +1,7 @@
 package com.sparrowwallet.drongo.crypto;
 
+import com.sparrowwallet.drongo.Utils;
+
 import java.nio.charset.StandardCharsets;
 import java.util.Objects;
 
@@ -9,8 +11,8 @@ public class EncryptionType {
             public KeyDeriver getKeyDeriver() {
                 return new KeyDeriver() {
                     @Override
-                    public Key deriveKey(String password) throws KeyCrypterException {
+                    public Key deriveKey(CharSequence password) throws KeyCrypterException {
-                        return new Key(password.getBytes(StandardCharsets.UTF_8), null, NONE);
+                        return new Key(Utils.toBytesUTF8(password), null, NONE);
                     }
 
                     @Override

src/main/java/com/sparrowwallet/drongo/crypto/KeyDeriver.java

@@ -7,7 +7,7 @@ public interface KeyDeriver {
      * @return Key The Key which typically contains the AES key to use for encrypting and decrypting
      * @throws KeyCrypterException
      */
-    Key deriveKey(String password) throws KeyCrypterException;
+    Key deriveKey(CharSequence password) throws KeyCrypterException;
 
     EncryptionType.Deriver getDeriverType();
 }

src/main/java/com/sparrowwallet/drongo/crypto/Pbkdf2KeyDeriver.java

@@ -1,11 +1,10 @@
 package com.sparrowwallet.drongo.crypto;
 
+import com.sparrowwallet.drongo.Utils;
 import org.bouncycastle.crypto.digests.SHA512Digest;
 import org.bouncycastle.crypto.generators.PKCS5S2ParametersGenerator;
 import org.bouncycastle.crypto.params.KeyParameter;
 
-import java.nio.charset.StandardCharsets;
-
 public class Pbkdf2KeyDeriver implements KeyDeriver, AsymmetricKeyDeriver {
     public static final int DEFAULT_ITERATION_COUNT = 1024;
 
@@ -35,15 +34,15 @@ public class Pbkdf2KeyDeriver implements KeyDeriver, AsymmetricKeyDeriver {
     }
 
     @Override
-    public Key deriveKey(String password) throws KeyCrypterException {
+    public Key deriveKey(CharSequence password) throws KeyCrypterException {
         PKCS5S2ParametersGenerator gen = new PKCS5S2ParametersGenerator(new SHA512Digest());
-        gen.init(password.getBytes(StandardCharsets.UTF_8), salt, iterationCount);
+        gen.init(Utils.toBytesUTF8(password), salt, iterationCount);
         byte[] keyBytes = ((KeyParameter)gen.generateDerivedParameters(512)).getKey();
         return new Key(keyBytes, salt, getDeriverType());
     }
 
     @Override
-    public ECKey deriveECKey(String password) throws KeyCrypterException {
+    public ECKey deriveECKey(CharSequence password) throws KeyCrypterException {
         Key key = deriveKey(password);
         return ECKey.fromPrivate(key.getKeyBytes());
     }

src/main/java/com/sparrowwallet/drongo/crypto/ScryptKeyDeriver.java

@@ -1,5 +1,6 @@
 package com.sparrowwallet.drongo.crypto;
 
+import com.sparrowwallet.drongo.Utils;
 import org.bouncycastle.crypto.generators.SCrypt;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -99,10 +100,10 @@ public class ScryptKeyDeriver implements KeyDeriver {
      * @throws            KeyCrypterException
      */
     @Override
-    public Key deriveKey(String password) throws KeyCrypterException {
+    public Key deriveKey(CharSequence password) throws KeyCrypterException {
         byte[] passwordBytes = null;
         try {
-            passwordBytes = convertToByteArray(password);
+            passwordBytes = Utils.toBytesUTF8(password);
             byte[] salt = new byte[0];
             if (scryptParameters.getSalt() != null) {
                 salt = scryptParameters.getSalt();
@@ -122,21 +123,6 @@ public class ScryptKeyDeriver implements KeyDeriver {
         }
     }
 
-    /**
-     * Convert a CharSequence (which are UTF16) into a byte array.
-     *
-     * Note: a String.getBytes() is not used to avoid creating a String of the password in the JVM.
-     */
-    private static byte[] convertToByteArray(CharSequence charSequence) {
-        byte[] byteArray = new byte[charSequence.length() << 1];
-        for(int i = 0; i < charSequence.length(); i++) {
-            int bytePosition = i << 1;
-            byteArray[bytePosition] = (byte) ((charSequence.charAt(i)&0xFF00)>>8);
-            byteArray[bytePosition + 1] = (byte) (charSequence.charAt(i)&0x00FF);
-        }
-        return byteArray;
-    }
-
     public ScryptParameters getScryptParameters() {
         return scryptParameters;
     }

src/main/java/com/sparrowwallet/drongo/wallet/DeterministicSeed.java

@@ -199,7 +199,7 @@ public class DeterministicSeed implements EncryptableItem {
         return mnemonicString.getBytes(StandardCharsets.UTF_8);
     }
 
-    public DeterministicSeed decrypt(String password) {
+    public DeterministicSeed decrypt(CharSequence password) {
         if(!isEncrypted()) {
             throw new IllegalStateException("Cannot decrypt unencrypted seed");
         }

src/main/java/com/sparrowwallet/drongo/wallet/Keystore.java

@@ -191,7 +191,7 @@ public class Keystore {
         }
     }
 
-    public void decrypt(String password) {
+    public void decrypt(CharSequence password) {
         if(hasSeed() && seed.isEncrypted()) {
             seed = seed.decrypt(password);
         }

src/main/java/com/sparrowwallet/drongo/wallet/Wallet.java

@@ -187,7 +187,7 @@ public class Wallet {
         }
     }
 
-    public void decrypt(String password) {
+    public void decrypt(CharSequence password) {
         for(Keystore keystore : keystores) {
             keystore.decrypt(password);
         }