From e81b8da855499c4902dff34780b2e196c57bc45a Mon Sep 17 00:00:00 2001
From: Benjamin Loison <benjamin.loison@orange.fr>
Date: Sun, 16 Apr 2023 20:19:33 +0200
Subject: [PATCH] Add difficulty verification to the verifier one

---
 common.py   |  9 ++++++++-
 prover.py   | 11 +++++------
 verifier.py |  9 ++++++---
 3 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/common.py b/common.py
index 0fa6fe7..0f4cd0a 100644
--- a/common.py
+++ b/common.py
@@ -8,6 +8,8 @@ MAXIMUM_HASH_DIFFICULTY = 1 / 16
 # The following space is a minimum.
 SPACE_TO_PROVE_IN_BITS = 1_000
 
+LEAST_DIFFICULT_HASH = int('F' * (SECURITY_PARAMETER // 4), 16)
+
 NUMBER_OF_BITS_IN_AVERAGE_FOR_SOLVING_PUZZLE = int(math.log2(1 / MAXIMUM_HASH_DIFFICULTY))
 ENTRIES_NUMBER = math.ceil(SPACE_TO_PROVE_IN_BITS // NUMBER_OF_BITS_IN_AVERAGE_FOR_SOLVING_PUZZLE)
 # To ease Merkle tree implementation use a power of 2 number of leafs.
@@ -24,4 +26,9 @@ def numberOfBitsOf(n):
     return math.floor(math.log2(n)) + 1
 
 def otherIndex(n):
-    return n + (1 if n % 2 == 0 else -1)
\ No newline at end of file
+    return n + (1 if n % 2 == 0 else -1)
+
+def doesHashMatchDifficulty(hashed):
+    hashedInteger = int(hashed, 16)
+    hashedDifficulty = hashedInteger / LEAST_DIFFICULT_HASH
+    return hashedDifficulty <= MAXIMUM_HASH_DIFFICULTY
\ No newline at end of file
diff --git a/prover.py b/prover.py
index cb88ee2..6247131 100755
--- a/prover.py
+++ b/prover.py
@@ -19,14 +19,10 @@ STORED_NONCES = []
 counter = 0
 lastCounter = 0
 
-LEAST_DIFFICULT_HASH = int('F' * (common.SECURITY_PARAMETER // 4), 16)
-
 # We enforce `STORED_NONCES` to have its length being a power of 2, to ease Merkle tree implementation.
 while len(STORED_NONCES) < common.ENTRIES_NUMBER:
     hashed = common.hash(protocolInitializationPhaseId + str(counter))
-    hashedInteger = int(hashed, 16)
-    hashedDifficulty = hashedInteger / LEAST_DIFFICULT_HASH
-    if hashedDifficulty <= common.MAXIMUM_HASH_DIFFICULTY:
+    if common.doesHashMatchDifficulty(hashed):
         deltaCounter = counter - lastCounter
         STORED_NONCES += [deltaCounter]
         lastCounter = counter
@@ -90,6 +86,7 @@ for indexRequest in indexesRequest:
     for index in [indexRequest, otherIndex]:
         verificationMerkleTreeLevels[0][index] = merkleTreeLevels[0][index]
 
+# Should rename `entries`, as they aren't *entries* for higher levels.
 entries = []
 for verificationMerkleTreeLevelsIndex, verificationMerkleTreeLevel in enumerate(verificationMerkleTreeLevels[:-1]):
     for index in verificationMerkleTreeLevel:
@@ -100,7 +97,9 @@ for verificationMerkleTreeLevelsIndex, verificationMerkleTreeLevel in enumerate(
         verificationMerkleTreeLevels[verificationMerkleTreeLevelsIndex + 1][leftIndex // 2] = common.hash(leftHash + rightHash)
         if verificationMerkleTreeLevelsIndex > 0 or leftIndex == index:
             if verificationMerkleTreeLevelsIndex == 0:
-                entries += [leftHash, rightHash]
+                leftNonce = sum(STORED_NONCES[:leftIndex + 1])
+                rightNonce = leftNonce + STORED_NONCES[rightIndex]
+                entries += [leftNonce, rightNonce]
             else:
                 entries += [otherHash]
 
diff --git a/verifier.py b/verifier.py
index 0a1f7ee..078931d 100755
--- a/verifier.py
+++ b/verifier.py
@@ -46,7 +46,6 @@ print(f'{indexesRequest=}')
 # Add mentions of rationality and code its factor? or/and precise when to run initialization and execution phases
 # TODO: precising `entries` size could be interesting.
 
-# TODO: verify hash difficulty - requires to send actual nonces
 # Proceeding in a minimum number of passes could be interesting but this can be left for future work.
 
 entries = ast.literal_eval(input('entries: '))
@@ -56,8 +55,12 @@ merkleTreeLevels = [{} for _ in range(common.LEVELS)]
 for index in indexesRequest:
     otherIndex = common.otherIndex(index)
     leftIndex, rightIndex = sorted([index, otherIndex])
-    for i, hash in zip([leftIndex, rightIndex], [entries.pop(0) for _ in range(2)]):
-        merkleTreeLevels[0][i] = hash
+    for i, nonce in zip([leftIndex, rightIndex], [entries.pop(0) for _ in range(2)]):
+        hashed = common.hash(protocolInitializationPhaseId + str(nonce))
+        if not common.doesHashMatchDifficulty(hashed):
+            print("The received difficulty doesn't match the claimed one!'")
+            exit(1)
+        merkleTreeLevels[0][i] = common.hash(protocolInitializationPhaseId + protocolExecutionPhaseId + str(nonce))
 
 for merkleTreeLevelsIndex, merkleTreeLevel in enumerate(merkleTreeLevels[:-1]):
     for index in merkleTreeLevel.copy():