commit 11daae87ada421e286a9261ca4758b96e0c00262
Author: Benjamin Loison <benjamin.loison@orange.fr>
Date:   Mon Apr 10 17:41:23 2023 +0200

    Add `{common, prover, verifier}.py`

diff --git a/common.py b/common.py
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--- /dev/null
+++ b/common.py
@@ -0,0 +1 @@
+SECURITY_PARAMETER = 256
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diff --git a/prover.py b/prover.py
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+++ b/prover.py
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+# Proof of Space-Time prover
+
+import math, common
+from hashlib import sha256
+
+SPACE_TO_PROVE_IN_BITS = 1_000
+MAXIMUM_HASH_DIFFICULTY = 0.1
+
+# 1. Receive a random bitstring from the verifier.
+
+protocolExecutionId = input('protocolExecutionId: ')
+
+# 2. Generate in a table the data that the prover has to store.
+# To ensure that this data is cheaper to store than to generate and to allow public verifiability by requiring the stored data to be Proof of Works.
+# For the ease of this implementation, the data are stored in the memory instead of the disk.
+
+STORED_DATA = []
+STORED_DATA_IN_BITS = 0
+counter = 0
+
+LEAST_DIFFICULT_HASH = int('F' * (common.SECURITY_PARAMETER // 4), 16)
+
+# We enforce `STORED_DATA` to have its length being a power of 2, to ease Merkle tree implementation.
+while STORED_DATA_IN_BITS < SPACE_TO_PROVE_IN_BITS or not math.log2(len(STORED_DATA)).is_integer():
+    print(STORED_DATA_IN_BITS, len(STORED_DATA))
+    # Note that for a production ready system hashing speedup (as designed for Bitcoin in [AsicBoost - A Speedup for Bitcoin Mining, Dr. Timo Hanke, March 31, 2016 (rev. 5)](https://arxiv.org/pdf/1604.00575.pdf)) should be considered.
+    hash = sha256((protocolExecutionId + str(counter)).encode('ascii')).hexdigest()
+    hashInteger = int(hash, 16)
+    hashDifficulty = hashInteger / LEAST_DIFFICULT_HASH
+    if hashDifficulty <= MAXIMUM_HASH_DIFFICULTY:
+        lastCounter = STORED_DATA[-1] if STORED_DATA != [] else -1
+        deltaCounter = counter - lastCounter
+        deltaCounterBits = math.ceil(math.log2(deltaCounter))
+        STORED_DATA += [deltaCounter]
+        STORED_DATA_IN_BITS += deltaCounterBits
+        print(hash, hashDifficulty, counter, lastCounter, deltaCounterBits)
+    counter += 1
+
+
diff --git a/verifier.py b/verifier.py
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+++ b/verifier.py
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+# Proof of Space-Time verifier
+
+import secrets, common
+
+# 1. Generate a random bitstring to send to the prover.
+# To make sure that the following protocol execution can't be used partially or totally by the prover to reduce the cost of another protocol execution.
+
+protocolExecutionId = ''.join(secrets.choice('0123456789abcdef') for _ in range(common.SECURITY_PARAMETER // 4))
+print(protocolExecutionId)
+
+# 2.
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