diff --git a/lib/src/model/transaction.dart b/lib/src/model/transaction.dart
index 669e9ba6..ab8fd267 100644
--- a/lib/src/model/transaction.dart
+++ b/lib/src/model/transaction.dart
@@ -375,9 +375,14 @@ class Transaction {
 
     Uint8List ownershipsBuffers = Uint8List(0);
     for (Ownership ownership in data!.ownerships!) {
+      final Uint8List bufAuthKeyLength = Uint8List.fromList(
+          toByteArray(ownership.authorizedPublicKeys!.length));
+
       final List<Uint8List> authorizedKeysBuffer = <Uint8List>[
-        Uint8List.fromList(<int>[ownership.authorizedPublicKeys!.length])
+        Uint8List.fromList(<int>[bufAuthKeyLength.length]),
+        bufAuthKeyLength
       ];
+
       for (AuthorizedKey authorizedKey in ownership.authorizedPublicKeys!) {
         authorizedKeysBuffer
             .add(Uint8List.fromList(hexToUint8List(authorizedKey.publicKey!)));
@@ -426,6 +431,15 @@ class Transaction {
       ]);
     }
 
+    final Uint8List bufOwnershipLength =
+        Uint8List.fromList(toByteArray(data!.ownerships!.length));
+    final Uint8List bufUCOTransferLength =
+        Uint8List.fromList(toByteArray(data!.ledger!.uco!.transfers!.length));
+    final Uint8List bufTokenTransferLength =
+        Uint8List.fromList(toByteArray(data!.ledger!.token!.transfers!.length));
+    final Uint8List bufRecipientLength =
+        Uint8List.fromList(toByteArray(data!.recipients!.length));
+
     return concatUint8List(<Uint8List>[
       encodeInt32(version!),
       Uint8List.fromList(hexToUint8List(address!)),
@@ -434,13 +448,17 @@ class Transaction {
       Uint8List.fromList(utf8.encode(data!.code!)),
       bufContentSize,
       Uint8List.fromList(utf8.encode(data!.content!)),
-      Uint8List.fromList(<int>[data!.ownerships!.length]),
+      Uint8List.fromList(<int>[bufOwnershipLength.length]),
+      bufOwnershipLength,
       ownershipsBuffers,
-      Uint8List.fromList(<int>[data!.ledger!.uco!.transfers!.length]),
+      Uint8List.fromList(<int>[bufUCOTransferLength.length]),
+      bufUCOTransferLength,
       ucoTransfersBuffers,
-      Uint8List.fromList(<int>[data!.ledger!.token!.transfers!.length]),
+      Uint8List.fromList(<int>[bufTokenTransferLength.length]),
+      bufTokenTransferLength,
       tokenTransfersBuffers,
-      Uint8List.fromList(<int>[data!.recipients!.length]),
+      Uint8List.fromList(<int>[bufRecipientLength.length]),
+      bufRecipientLength,
       recipients
     ]);
   }
diff --git a/lib/src/utils/utils.dart b/lib/src/utils/utils.dart
index 05254cd0..cba36269 100644
--- a/lib/src/utils/utils.dart
+++ b/lib/src/utils/utils.dart
@@ -81,3 +81,21 @@ BigInt toBigInt(double? number) {
   number = number * pow(10, 8);
   return BigInt.from(number.toInt());
 }
+
+/// Convert any number into a byte array
+Uint8List toByteArray(int value) {
+  final BigInt byteMask = BigInt.from(0xff);
+  BigInt number = BigInt.from(value);
+  // Not handling negative numbers. Decide how you want to do that.
+  final int size = (number.bitLength + 7) >> 3;
+  if (size == 0) {
+    return Uint8List.fromList([0]);
+  }
+
+  Uint8List result = Uint8List(size);
+  for (int i = 0; i < size; i++) {
+    result[size - i - 1] = (number & byteMask).toInt();
+    number = number >> 8;
+  }
+  return result;
+}
diff --git a/pubspec.lock b/pubspec.lock
index 5aa457e0..00185de7 100644
--- a/pubspec.lock
+++ b/pubspec.lock
@@ -535,7 +535,7 @@ packages:
       name: pointycastle
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "3.6.0"
+    version: "3.6.1"
   pool:
     dependency: transitive
     description:
diff --git a/test/transaction_test.dart b/test/transaction_test.dart
index 374c401d..c1a8a380 100644
--- a/test/transaction_test.dart
+++ b/test/transaction_test.dart
@@ -159,11 +159,15 @@ void main() {
           //Content size
           encodeInt32(content.length),
           Uint8List.fromList(utf8.encode(content)),
+          //Nb of bytes to encode nb of ownerships
+          Uint8List.fromList(<int>[1]),
           //Nb of ownerships
           Uint8List.fromList(<int>[1]),
           //Secret size
           encodeInt32(Uint8List.fromList(hexToUint8List(secret)).lengthInBytes),
           Uint8List.fromList(Uint8List.fromList(hexToUint8List(secret))),
+          // Nb of byte to encode nb of authorized keys
+          Uint8List.fromList(<int>[1]),
           // Nb of authorized keys
           Uint8List.fromList(<int>[1]),
           // Authorized keys encoding
@@ -173,6 +177,8 @@ void main() {
             Uint8List.fromList(hexToUint8List(
                 '00501fa2db78bcf8ceca129e6139d7e38bf0d61eb905441056b9ebe6f1d1feaf88'))
           ]),
+          // Nb of bytes to encode nb of uco transfers
+          Uint8List.fromList(<int>[1]),
           // Nb of uco transfers
           Uint8List.fromList(<int>[1]),
           concatUint8List(<Uint8List>[
@@ -180,6 +186,8 @@ void main() {
                 '0000b1d3750edb9381c96b1a975a55b5b4e4fb37bfab104c10b0b6c9a00433ec4646')),
             encodeBigInt(toBigInt(0.2020))
           ]),
+          // Nb of byte to encode nb of Token transfers
+          Uint8List.fromList(<int>[1]),
           // Nb of token transfers
           Uint8List.fromList(<int>[1]),
           concatUint8List(<Uint8List>[
@@ -190,6 +198,8 @@ void main() {
             encodeBigInt(toBigInt(100)),
             Uint8List.fromList(<int>[0])
           ]),
+          // Nb of byte to encode nb of recipients
+          Uint8List.fromList(<int>[1]),
           // Nb of recipients
           Uint8List.fromList(<int>[1]),
           Uint8List.fromList(hexToUint8List(
@@ -301,11 +311,15 @@ void main() {
           //Content size
           encodeInt32(content.length),
           Uint8List.fromList(utf8.encode(content)),
+          // Nb of byte to encode nb of ownerships
+          Uint8List.fromList(<int>[1]),
           //Nb of ownerships
           Uint8List.fromList(<int>[1]),
           //Secret size
           encodeInt32(Uint8List.fromList(hexToUint8List(secret)).lengthInBytes),
           Uint8List.fromList(Uint8List.fromList(hexToUint8List(secret))),
+          // Nb of bytes to encode nb of authorized key
+          Uint8List.fromList(<int>[1]),
           // Nb of authorized keys
           Uint8List.fromList(<int>[1]),
           // Authorized keys encoding
@@ -315,6 +329,8 @@ void main() {
             Uint8List.fromList(hexToUint8List(
                 '00501fa2db78bcf8ceca129e6139d7e38bf0d61eb905441056b9ebe6f1d1feaf88'))
           ]),
+          // Nb of bytes to encode nb of uco transfers
+          Uint8List.fromList(<int>[1]),
           // Nb of uco transfers
           Uint8List.fromList(<int>[1]),
           concatUint8List(<Uint8List>[
@@ -322,6 +338,8 @@ void main() {
                 '0000b1d3750edb9381c96b1a975a55b5b4e4fb37bfab104c10b0b6c9a00433ec4646')),
             encodeBigInt(toBigInt(0.2020))
           ]),
+          // Nb of bytes to encode nb of Token transfers
+          Uint8List.fromList(<int>[1]),
           // Nb of token transfers
           Uint8List.fromList(<int>[1]),
           concatUint8List(<Uint8List>[
@@ -332,6 +350,8 @@ void main() {
             encodeBigInt(toBigInt(100)),
             Uint8List.fromList(<int>[0]),
           ]),
+          // Nb of bytes to encode nb of recipients
+          Uint8List.fromList(<int>[1]),
           // Nb of recipients
           Uint8List.fromList(<int>[1]),
           Uint8List.fromList(hexToUint8List(
diff --git a/test/utils_test.dart b/test/utils_test.dart
index 94a6f29f..5cabef76 100644
--- a/test/utils_test.dart
+++ b/test/utils_test.dart
@@ -63,4 +63,14 @@ void main() {
       expect(toBigInt(1.234567), BigInt.from(123456700));
     });
   });
+
+  group('toByteArray', () {
+    test('should encode an integer into a Uint8List', () {
+      expect(toByteArray(0), <int>[0]);
+      expect(toByteArray(123), <int>[123]);
+      expect(toByteArray(258), <int>[1, 2]);
+      expect(toByteArray(65535), <int>[255, 255]);
+      expect(toByteArray(65536), <int>[1, 0, 0]);
+    });
+  });
 }