refactor: update sign function PE-1136

Author: javdhu

lib/src/models/data_item.dart

@@ -138,9 +138,8 @@ class DataItem implements TransactionBase {
   /// Signs the [DataItem] using the specified wallet and sets the `id` and `signature` appropriately.
   @override
   Future<Uint8List> sign(Wallet wallet) async {
-    final rawSignature = await wallet.sign(this);
-
-    _signature = encodeBytesToBase64(rawSignature);
+    _signature = await wallet.sign(this);
+    final rawSignature = decodeBase64ToBytes(_signature);
 
     final idHash = await sha256.hash(rawSignature);
     _id = encodeBytesToBase64(idHash.bytes);

lib/src/models/transaction.dart

@@ -277,9 +277,8 @@ class Transaction implements TransactionBase {
 
   @override
   Future<void> sign(Wallet wallet) async {
-    final rawSignature = await wallet.sign(this);
-
-    _signature = encodeBytesToBase64(rawSignature);
+    _signature = await wallet.sign(this);
+    final rawSignature = decodeBase64ToBytes(_signature);
 
     final idHash = await sha256.hash(rawSignature);
     _id = encodeBytesToBase64(idHash.bytes);

lib/src/models/wallet.dart

@@ -55,8 +55,14 @@ class Wallet {
       await _keyPair!.extractPublicKey().then((res) => res.n));
   Future<String> getAddress() async => ownerToAddress(await getOwner());
 
-  Future<Uint8List> sign(TransactionBase transaction) async => rsaPssSign(
-      message: await transaction.getSignatureData(), keyPair: _keyPair!);
+  Future<String> sign(TransactionBase transaction) async {
+    return encodeBytesToBase64(
+      await rsaPssSign(
+        message: await transaction.getSignatureData(),
+        keyPair: _keyPair!,
+      ),
+    );
+  }
 
   Future<Uint8List> signMessage(Uint8List message) async =>
       rsaPssSign(message: message, keyPair: _keyPair!);