From 799550dd234b1a6e1881b269215aeaf8941a36e2 Mon Sep 17 00:00:00 2001
From: mac <mac@macs-MacBook-Pro.local>
Date: Sun, 5 Jul 2026 02:11:05 +0530
Subject: [PATCH 1/3] fix: validate proof of work on block acceptance

---
 minichain/chain.py           |  4 ++++
 tests/test_pow_validation.py | 37 ++++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)
 create mode 100644 tests/test_pow_validation.py

diff --git a/minichain/chain.py b/minichain/chain.py
index fa7d0dd..de9a007 100644
--- a/minichain/chain.py
+++ b/minichain/chain.py
@@ -25,6 +25,10 @@ def validate_block_link_and_hash(previous_block, block):
     if block.hash != expected_hash:
         raise ValueError(f"invalid hash {block.hash}")
 
+    if not block.hash.startswith("0" * block.difficulty):
+        raise ValueError(
+            f"invalid PoW: hash {block.hash} does not satisfy difficulty {block.difficulty}"
+        )
 
 class Blockchain:
     """
diff --git a/tests/test_pow_validation.py b/tests/test_pow_validation.py
new file mode 100644
index 0000000..6a2f4da
--- /dev/null
+++ b/tests/test_pow_validation.py
@@ -0,0 +1,37 @@
+from minichain import Blockchain, Block
+from minichain.validators import ValidationStatus
+
+
+def _make_block_with_invalid_pow(chain):
+    block = Block(
+        index=chain.last_block.index + 1,
+        previous_hash=chain.last_block.hash,
+        transactions=[],
+        difficulty=chain.current_difficulty,
+        state_root=chain.state.state_root(),
+    )
+
+    while True:
+        block.hash = block.compute_hash()
+        if not block.hash.startswith("0" * block.difficulty):
+            return block
+        block.nonce += 1
+
+
+def test_add_block_rejects_invalid_pow():
+    chain = Blockchain()
+    block = _make_block_with_invalid_pow(chain)
+
+    assert chain.add_block(block) == ValidationStatus.INVALID
+    assert len(chain.chain) == 1
+
+
+def test_resolve_conflicts_rejects_invalid_pow():
+    chain = Blockchain()
+    block = _make_block_with_invalid_pow(chain)
+
+    success, _ = chain.resolve_conflicts([chain.chain[0], block])
+
+    assert success is False
+    assert len(chain.chain) == 1
+    
\ No newline at end of file

From 24636cf154ba81ac547268a4fdfb5e4d04f1557c Mon Sep 17 00:00:00 2001
From: mac <mac@macs-MacBook-Pro.local>
Date: Sun, 5 Jul 2026 03:18:43 +0530
Subject: [PATCH 2/3] fix: handle invalid proof of work explicitly

---
 minichain/chain.py | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/minichain/chain.py b/minichain/chain.py
index de9a007..cdbef56 100644
--- a/minichain/chain.py
+++ b/minichain/chain.py
@@ -10,6 +10,10 @@
 logger = logging.getLogger(__name__)
 
 
+class InvalidProofOfWorkError(ValueError):
+    pass
+
+
 def validate_block_link_and_hash(previous_block, block):
     if block.previous_hash != previous_block.hash:
         raise ValueError(
@@ -26,7 +30,7 @@ def validate_block_link_and_hash(previous_block, block):
         raise ValueError(f"invalid hash {block.hash}")
 
     if not block.hash.startswith("0" * block.difficulty):
-        raise ValueError(
+        raise InvalidProofOfWorkError(
             f"invalid PoW: hash {block.hash} does not satisfy difficulty {block.difficulty}"
         )
 
@@ -143,11 +147,13 @@ def _apply_block(self, prev_block, block, state, difficulty, avg_block_time):
 
         try:
             validate_block_link_and_hash(prev_block, block)
+        except InvalidProofOfWorkError as exc:
+            logger.warning("Block %s rejected: %s", block.index, exc)
+            return ValidationStatus.INVALID, difficulty, avg_block_time
         except ValueError as exc:
             logger.warning("Block %s rejected: %s", block.index, exc)
             status = ValidationStatus.INVALID if "hash" in str(exc) else ValidationStatus.FAILED
             return status, difficulty, avg_block_time
-
         if block.difficulty != difficulty:
             logger.warning("Block %s rejected: Invalid difficulty. Expected %s, got %s", block.index, difficulty, block.difficulty)
             return ValidationStatus.INVALID, difficulty, avg_block_time

From 94231730f1eb6e68ad75df7635b5c0e5ac015d91 Mon Sep 17 00:00:00 2001
From: mac <mac@macs-MacBook-Pro.local>
Date: Mon, 6 Jul 2026 17:22:24 +0530
Subject: [PATCH 3/3] style: remove trailing whitespace

---
 tests/test_pow_validation.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/tests/test_pow_validation.py b/tests/test_pow_validation.py
index 6a2f4da..77695a5 100644
--- a/tests/test_pow_validation.py
+++ b/tests/test_pow_validation.py
@@ -34,4 +34,3 @@ def test_resolve_conflicts_rejects_invalid_pow():
 
     assert success is False
     assert len(chain.chain) == 1
-    
\ No newline at end of file