Solve potential length extension attack by using SHA-3

common.py

@@ -1,5 +1,5 @@
 import math
-from hashlib import sha256
+from hashlib import sha3_256
 
 SECURITY_PARAMETER = 256
 # Note that notably `MAXIMUM_HASH_DIFFICULTY` and `SPACE_TO_PROVE_IN_BITS` should be sent from the prover to the verifier before the second verifier initialization step. However to ease this prototype this communication isn't performed.
@@ -29,9 +29,8 @@ ENTRIES_NUMBER = math.ceil(SPACE_TO_PROVE_IN_BITS / NUMBER_OF_BITS_IN_AVERAGE_FO
 ENTRIES_NUMBER = 2 ** math.ceil(math.log2(ENTRIES_NUMBER))
 LEVELS = int(math.log2(ENTRIES_NUMBER)) + 1
 
-# Do we have a problem due to length extension attacks? If so, could sha256 one more time as in Bitcoin.
 def hash(x):
-    return sha256(x.encode('ascii')).hexdigest()
+    return sha3_256(x.encode('ascii')).hexdigest()
 
 # Storage could be done by using a separator but is it optimal? In fact how to do a separator optimally in binary? Could for instance encode on two bits, for normal bits the first one should be 0 otherwise if the first is 1 then whatever the second bit, it's a separator.
 # TODO: sure that this function is meaningly correct? cf below comment, should also consider the serialization of the actual array - should in a similar way verify `ENTRIES_NUMBER` computation

meta.py

@@ -34,9 +34,6 @@ while True:
     write(prover, 'indexesRequest.txt')
     getProgramLine(prover)
 
-    with open('indexesRequest.txt') as f:
-        print(f.read())
-
     write(verifier, 'entries.txt')
     result = ' '.join(getProgramLine(verifier).split()[1:])
     print(result)