feat: Add Ethereum-style timestamp validation and PoW hash check

minichain/chain.py

@@ -6,6 +6,7 @@
 import json
 import os
 import sys
+import time
 
 logger = logging.getLogger(__name__)
 
@@ -25,6 +26,17 @@ def validate_block_link_and_hash(previous_block, block):
     if block.hash != expected_hash:
         raise ValueError(f"invalid hash {block.hash}")
 
+    target = "0" * (block.difficulty or 1)
+    if not block.hash.startswith(target):
+        raise ValueError(f"invalid Proof of Work: hash {block.hash} does not satisfy difficulty {block.difficulty}")
+
+    if block.timestamp <= previous_block.timestamp:
+        raise ValueError(f"invalid timestamp: {block.timestamp} is not strictly greater than previous block timestamp {previous_block.timestamp}")
+
+    max_allowed_time = int(time.time() * 1000) + 15000
+    if block.timestamp > max_allowed_time:
+        raise ValueError(f"invalid timestamp: {block.timestamp} is too far in the future (max allowed: {max_allowed_time})")
+
 
 class Blockchain:
     """

tests/test_persistence.py

@@ -54,7 +54,7 @@ def _chain_with_tx(self):
             state_root=temp_state.state_root(),
             receipt_root=calculate_receipt_root([receipt]),
             receipts=[receipt],
-            timestamp=int(time.time()),
+            timestamp=bc.last_block.timestamp + 1000,
         )
         mine_block(block)
         bc.add_block(block)
@@ -249,7 +249,7 @@ def test_loaded_chain_can_add_new_block(self):
             state_root=temp_state.state_root(),
             receipt_root=calculate_receipt_root([receipt2]),
             receipts=[receipt2],
-            timestamp=int(time.time()),
+            timestamp=restored.last_block.timestamp + 1000,
         )
         mine_block(block2)