diff --git a/main.py b/main.py
index e1edc51..b39de4c 100644
--- a/main.py
+++ b/main.py
@@ -78,9 +78,10 @@ def mine_and_process_block(chain, mempool, miner_pk):
         return None
 
     block = Block(
-        index=chain.last_block.index + 1,
-        previous_hash=chain.last_block.hash,
-        transactions=mineable_txs,
+    index=chain.last_block.index + 1,
+    previous_hash=chain.last_block.hash,
+    transactions=mineable_txs,
+    miner=miner_pk,  # ← ADD THIS
     )
 
     mined_block = mine_block(block)
@@ -238,7 +239,7 @@ async def cli_loop(sk, pk, chain, mempool, network):
         elif cmd == "mine":
             mined = mine_and_process_block(chain, mempool, pk)
             if mined:
-                await network.broadcast_block(mined, miner=pk)
+                await network.broadcast_block(mined)  # ← just this, no miner assignment above it
 
         # ── peers ──
         elif cmd == "peers":
diff --git a/minichain/block.py b/minichain/block.py
index 9854cf4..fabb768 100644
--- a/minichain/block.py
+++ b/minichain/block.py
@@ -1,14 +1,17 @@
 import time
 import hashlib
-from typing import List, Optional
+from typing import Optional  # <-- Removed 'List' as requested
+from collections.abc import Sequence
+
 from .transaction import Transaction
-from .serialization import canonical_json_hash
+from .serialization import canonical_json_hash, canonical_json_bytes
+
 
 def _sha256(data: str) -> str:
     return hashlib.sha256(data.encode()).hexdigest()
 
-
-def _calculate_merkle_root(transactions: List[Transaction]) -> Optional[str]:
+# <-- Updated to Sequence to accept the frozen tuple
+def _calculate_merkle_root(transactions: Sequence[Transaction]) -> Optional[str]:
     if not transactions:
         return None
 
@@ -32,27 +35,27 @@ def _calculate_merkle_root(transactions: List[Transaction]) -> Optional[str]:
 
     return tx_hashes[0]
 
-
 class Block:
     def __init__(
         self,
         index: int,
         previous_hash: str,
-        transactions: Optional[List[Transaction]] = None,
+        transactions: Optional[list[Transaction]] = None,  # <-- Updated to built-in 'list'
         timestamp: Optional[float] = None,
         difficulty: Optional[int] = None,
+        miner: Optional[str] = None
     ):
         self.index = index
         self.previous_hash = previous_hash
-        self.transactions: List[Transaction] = transactions or []
-
+        # Freeze transactions into an immutable tuple to prevent header/body mismatch
+        self.transactions = tuple(transactions) if transactions else ()
+        self.miner = miner
         # Deterministic timestamp (ms)
         self.timestamp: int = (
             round(time.time() * 1000)
             if timestamp is None
             else int(timestamp)
         )
-
         self.difficulty: Optional[int] = difficulty
         self.nonce: int = 0
         self.hash: Optional[str] = None
@@ -64,7 +67,7 @@ def __init__(
     # HEADER (used for mining)
     # -------------------------
     def to_header_dict(self):
-        return {
+        header = {
             "index": self.index,
             "previous_hash": self.previous_hash,
             "merkle_root": self.merkle_root,
@@ -72,7 +75,11 @@ def to_header_dict(self):
             "difficulty": self.difficulty,
             "nonce": self.nonce,
         }
-
+        # Include miner in header only when present (optional field)  <-- Reworded comment
+        if self.miner is not None:
+            header["miner"] = self.miner          
+        return header
+        
     # -------------------------
     # BODY (transactions only)
     # -------------------------
@@ -87,11 +94,10 @@ def to_body_dict(self):
     # FULL BLOCK
     # -------------------------
     def to_dict(self):
-        return {
-            **self.to_header_dict(),
-            **self.to_body_dict(),
-            "hash": self.hash,
-        }
+        data = self.to_header_dict()
+        data.update(self.to_body_dict()) # Reuses existing serialization logic
+        data["hash"] = self.hash
+        return data
 
     # -------------------------
     # HASH CALCULATION
@@ -105,15 +111,43 @@ def from_dict(cls, payload: dict):
             Transaction.from_dict(tx_payload)
             for tx_payload in payload.get("transactions", [])
         ]
+        
+        # Safely extract and cast difficulty if it exists
+        raw_diff = payload.get("difficulty")
+        parsed_diff = int(raw_diff) if raw_diff is not None else None
+        
+        # Safely extract and cast timestamp if it exists <-- Added explicit timestamp casting
+        raw_ts = payload.get("timestamp")
+        parsed_ts = int(raw_ts) if raw_ts is not None else None
+        
         block = cls(
-            index=payload["index"],
+            index=int(payload["index"]),  
             previous_hash=payload["previous_hash"],
             transactions=transactions,
-            timestamp=payload.get("timestamp"),
-            difficulty=payload.get("difficulty"),
+            timestamp=parsed_ts,          # <-- Passed the casted timestamp
+            difficulty=parsed_diff,       
+            miner=payload.get("miner"),
         )
-        block.nonce = payload.get("nonce", 0)
+        block.nonce = int(payload.get("nonce", 0))  
         block.hash = payload.get("hash")
-        if "merkle_root" in payload:
-            block.merkle_root = payload["merkle_root"]
+      
+        # Verify the block hash
+        expected_hash = block.compute_hash()
+        if block.hash is not None and block.hash != expected_hash:
+            raise ValueError("block hash does not match header")
+
+        # Recalculate and verify the Merkle root!
+        if "merkle_root" in payload and payload["merkle_root"] != block.merkle_root:
+            raise ValueError("merkle_root does not match transactions")
         return block
+
+    @property
+    def canonical_payload(self) -> bytes:
+        """Returns the full block (header + body) as canonical bytes for networking."""
+        # Sanity checks to prevent broadcasting invalid blocks
+        if self.hash is None:
+            raise ValueError("block hash is missing")
+        if self.hash != self.compute_hash():
+            raise ValueError("block hash does not match header")
+        
+        return canonical_json_bytes(self.to_dict())
\ No newline at end of file
diff --git a/minichain/p2p.py b/minichain/p2p.py
index 3271598..2be7436 100644
--- a/minichain/p2p.py
+++ b/minichain/p2p.py
@@ -9,7 +9,7 @@
 import json
 import logging
 
-from .serialization import canonical_json_hash
+from .serialization import canonical_json_hash, canonical_json_dumps
 from .validators import is_valid_receiver
 
 logger = logging.getLogger(__name__)
@@ -58,9 +58,7 @@ async def _notify_peer_connected(self, writer, error_message):
     async def start(self, port: int = 9000, host: str = "127.0.0.1"):
         """Start listening for incoming peer connections on the given port."""
         self._port = port
-        self._server = await asyncio.start_server(
-            self._handle_incoming, host, port
-        )
+        self._server = await asyncio.start_server(self._handle_incoming, host, port)
         logger.info("Network: Listening on %s:%d", host, port)
 
     async def stop(self):
@@ -208,7 +206,9 @@ def _validate_block_payload(self, payload):
         )
 
     def _validate_message(self, message):
+        # FIX: Check if message is a dictionary first to prevent crashes
         if not isinstance(message, dict):
+            logger.warning("Network: Received non-dict message")
             return False
         required_fields = {"type", "data"}
         if not required_fields.issubset(set(message)):
@@ -307,7 +307,7 @@ async def _listen_to_peer(
 
     async def _broadcast_raw(self, payload: dict):
         """Send a JSON message to every connected peer."""
-        line = (json.dumps(payload) + "\n").encode()
+        line = (canonical_json_dumps(payload) + "\n").encode()
         disconnected = []
         for reader, writer in self._peers:
             try:
@@ -336,12 +336,19 @@ async def broadcast_transaction(self, tx):
         self._mark_seen("tx", payload["data"])
         await self._broadcast_raw(payload)
 
-    async def broadcast_block(self, block, miner=None):
+    async def broadcast_block(self, block):
+        """Broadcast a block. Block must have miner populated."""
         logger.info("Network: Broadcasting Block #%d", block.index)
-        block_payload = block.to_dict()
-        if miner is not None:
-            block_payload["miner"] = miner
-        payload = {"type": "block", "data": block_payload}
+
+        # Enforce that the block is fully populated before it enters the network layer
+        if getattr(block, "miner", None) is None:
+            raise ValueError("block.miner must be populated before broadcasting")
+
+        payload = {
+            "type": "block",
+            "data": json.loads(block.canonical_payload.decode("utf-8"))
+        }
+
         self._mark_seen("block", payload["data"])
         await self._broadcast_raw(payload)
 
diff --git a/tests/test_serialization.py b/tests/test_serialization.py
new file mode 100644
index 0000000..aa5f2b7
--- /dev/null
+++ b/tests/test_serialization.py
@@ -0,0 +1,88 @@
+from minichain.serialization import canonical_json_hash
+from minichain.transaction import Transaction
+from minichain.block import Block
+
+def test_raw_data_determinism():
+    print("--- Testing Raw Data Determinism ---")
+    # Same data, different key order
+    data_v1 = {"amount": 100, "nonce": 1, "receiver": "Alice", "sender": "Bob"}
+    data_v2 = {"sender": "Bob", "receiver": "Alice", "nonce": 1, "amount": 100}
+
+    hash_1 = canonical_json_hash(data_v1)
+    hash_2 = canonical_json_hash(data_v2)
+
+    print(f"Hash 1: {hash_1}")
+    print(f"Hash 2: {hash_2}")
+    assert hash_1 == hash_2
+    print("Success: Raw hashes match regardless of key order!\n")
+
+def test_transaction_id_stability():
+    print("--- Testing Transaction ID Stability ---")
+    # FIX: Add a fixed timestamp so tx1 and tx2 are identical
+    tx_params = {"sender": "Alice", "receiver": "Bob", "amount": 50, "nonce": 1, "timestamp": 123456789}
+    
+    tx1 = Transaction(**tx_params)
+    tx2 = Transaction(**tx_params)
+
+    print(f"TX ID: {tx1.tx_id}")
+    assert tx1.tx_id == tx2.tx_id, "Cross-instance TX IDs must match with same timestamp"
+    print("✅ Success: Transaction ID is stable!\n")
+
+def test_block_serialization_determinism():
+    print("--- Testing Block Serialization & Cross-Instance Determinism ---")
+    # FIX: Use fixed timestamps for both transaction and block
+    tx_params = {"sender": "A", "receiver": "B", "amount": 10, "nonce": 5, "timestamp": 1000}
+    
+    # Create two separate but identical transaction instances
+    tx1 = Transaction(**tx_params)
+    tx2 = Transaction(**tx_params)
+    
+   # Add the miner field
+    block1 = Block(index=1, previous_hash="0"*64, transactions=[tx1], difficulty=2, timestamp=999999, miner="a" * 40)
+    block2 = Block(index=1, previous_hash="0"*64, transactions=[tx2], difficulty=2, timestamp=999999, miner="a" * 40)
+
+    # Pre-compute the hashes before asserting
+    block1.hash = block1.compute_hash()
+    block2.hash = block2.compute_hash()
+
+    assert block1.canonical_payload == block2.canonical_payload, "Identical blocks must have identical payloads"
+    assert block1.compute_hash() == block2.compute_hash(), "Identical blocks must have identical hashes"
+    
+    print("✅ Success: Block serialization is cross-instance deterministic!\n")
+
+def test_block_from_dict_rejects_tampered_payload():
+    print("--- Testing Tamper Rejection ---")
+    tx = Transaction(sender="A", receiver="B", amount=10, nonce=5, timestamp=1000)
+    block = Block(
+        index=1, previous_hash="0"*64, transactions=[tx], 
+        difficulty=2, timestamp=999999, miner="a"*40
+    )
+    block.hash = block.compute_hash()
+
+    # Test tampered Merkle Root (only one instance needed)
+    bad_merkle = block.to_dict()
+    bad_merkle["merkle_root"] = "f" * 64
+    try:
+        Block.from_dict(bad_merkle)
+        raise AssertionError("Expected ValueError for tampered merkle_root") # Robust error
+    except ValueError:
+        pass
+
+    # Test tampered Hash
+    bad_hash = block.to_dict()
+    bad_hash["hash"] = "0" * 64
+    try:
+        Block.from_dict(bad_hash)
+        raise AssertionError("Expected ValueError for tampered hash")
+    except ValueError:
+        pass
+    
+    print("✅ Success: Tampered payloads are rejected!\n")
+
+if __name__ == "__main__":
+    # Removed try/except so that AssertionErrors 'bubble up' to the test runner
+    test_raw_data_determinism()
+    test_transaction_id_stability()
+    test_block_serialization_determinism()
+    test_block_from_dict_rejects_tampered_payload()  # <--- ADDED THIS LINE
+    print("🚀 ALL CANONICAL TESTS PASSED!")
\ No newline at end of file