diff --git a/src/main/scala/com/fluency03/blockchain/Crypto.scala b/src/main/scala/com/fluency03/blockchain/Crypto.scala
index 1e41186..098abde 100644
--- a/src/main/scala/com/fluency03/blockchain/Crypto.scala
+++ b/src/main/scala/com/fluency03/blockchain/Crypto.scala
@@ -17,7 +17,7 @@ object Crypto {
 
   val ecSpec: ECParameterSpec = ECNamedCurveTable.getParameterSpec(SPECP256K1)
 
-  def sign(data: Array[Byte], privateKey: Array[Byte]): Array[Byte] = {
+  def sign(data: Bytes, privateKey: Bytes): Bytes = {
     val keySpec: PKCS8EncodedKeySpec = new PKCS8EncodedKeySpec(privateKey)
     val keyFactory: KeyFactory = KeyFactory.getInstance(KEY_ALGORITHM)
     val key: PrivateKey = keyFactory.generatePrivate(keySpec)
@@ -28,7 +28,7 @@ object Crypto {
     sig.sign()
   }
 
-  def verify(data: Array[Byte], publicKey: Array[Byte], signature: Array[Byte]): Boolean =  {
+  def verify(data: Bytes, publicKey: Bytes, signature: Bytes): Boolean =  {
     val keySpec: X509EncodedKeySpec = new X509EncodedKeySpec(publicKey)
     val keyFactory: KeyFactory = KeyFactory.getInstance(KEY_ALGORITHM)
     val key: PublicKey = keyFactory.generatePublic(keySpec)
diff --git a/src/main/scala/com/fluency03/blockchain/Util.scala b/src/main/scala/com/fluency03/blockchain/Util.scala
index a960e72..67e57d2 100644
--- a/src/main/scala/com/fluency03/blockchain/Util.scala
+++ b/src/main/scala/com/fluency03/blockchain/Util.scala
@@ -17,7 +17,7 @@ object Util {
    * Generate digest from a input String.
    * https://gist.github.com/navicore/6234040bbfce3aa58f866db314c07c15
    */
-  def digestOf(text: String): Array[Byte] =
+  def digestOf(text: String): Bytes =
     MessageDigest.getInstance("SHA-256").digest(text.getBytes("UTF-8"))
 
   /**
@@ -53,7 +53,7 @@ object Util {
   /**
    * Encode an Array of Bytes String to Base64.
    */
-  def base64Of(data: Array[Byte]): String = Base64.toBase64String(data)
+  def base64Of(data: Bytes): String = Base64.toBase64String(data)
 
   /**
    * Decode a Base64 to String.
diff --git a/src/main/scala/com/fluency03/blockchain/core/Transaction.scala b/src/main/scala/com/fluency03/blockchain/core/Transaction.scala
index ff327b7..2014cbc 100644
--- a/src/main/scala/com/fluency03/blockchain/core/Transaction.scala
+++ b/src/main/scala/com/fluency03/blockchain/core/Transaction.scala
@@ -64,7 +64,7 @@ object Transaction {
   )
 
   def signTxIn(
-      txId: Array[Byte],
+      txId: Bytes,
       txIn: TxIn,
       keyPair: KeyPair,
       unspentTxOuts: mutable.Map[Outpoint, TxOut]
@@ -78,7 +78,7 @@ object Transaction {
   def validateTxIn(txIn: TxIn, txId: String, unspentTxOuts: mutable.Map[Outpoint, TxOut]): Boolean =
     validateTxIn(txIn, txId.hex2Bytes, unspentTxOuts)
 
-  def validateTxIn(txIn: TxIn, txId: Array[Byte], unspentTxOuts: mutable.Map[Outpoint, TxOut]): Boolean =
+  def validateTxIn(txIn: TxIn, txId: Bytes, unspentTxOuts: mutable.Map[Outpoint, TxOut]): Boolean =
     unspentTxOuts.get(txIn.previousOut) match {
       case Some(txOut) => Crypto.verify(txId, txOut.address.hex2Bytes, txIn.signature.hex2Bytes)
       case None => false
diff --git a/src/test/scala/com/fluency03/blockchain/UtilTest.scala b/src/test/scala/com/fluency03/blockchain/UtilTest.scala
index 564e34c..4468ea5 100644
--- a/src/test/scala/com/fluency03/blockchain/UtilTest.scala
+++ b/src/test/scala/com/fluency03/blockchain/UtilTest.scala
@@ -57,4 +57,22 @@ class UtilTest extends FlatSpec with Matchers with MockFactory {
     an[NumberFormatException] should be thrownBy binaryOfHex("g")
   }
 
+  "StringImplicit" should "convert String to corresponding type." in {
+    fromBase64("open sesame".toBase64) shouldEqual "open sesame"
+    "open sesame".toSha256 shouldEqual "41ef4bb0b23661e66301aac36066912dac037827b4ae63a7b1165a5aa93ed4eb"
+    "".toSha256 shouldEqual "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
+    "a".hex2Binary shouldEqual "1010"
+    "ab".hex2Binary shouldEqual "10101011"
+  }
+
+  "BytesImplicit" should "convert Array of Byte to corresponding type." in {
+    val bytes: Bytes = Array(192.toByte, 168.toByte, 1, 9)
+    bytes.toHex shouldEqual "c0a80109"
+    bytes.toBase64 shouldEqual "wKgBCQ=="
+  }
+
+  "genesisTimestamp" should "be the Epoch time of 2018-04-11T18:52:01Z ." in {
+    genesisTimestamp shouldEqual 1523472721
+  }
+
 }