initial commit

.gitignore

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+*.pyc
+__pycache__

shark.py

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+import hashlib
+import math
+
+# Shark is a sha256+xor based encryption.
+# I made it because I want to try to break it.
+# (Precisely: Show it does not provide semantic security, because it is not IND-CPA-secure)
+# This will work iff I succeed in building a PPT-discriminator for sha256 from randomness
+# As my first approach this discriminator will be based on an LSTM-network.
+
+def xor(ta,tb):
+    return bytes(a ^ b for a, b in zip(ta, tb))
+
+def enc(plaintext, key, iv):
+    ciphertext = bytes()
+    bs = 256/8
+    for i in range(math.ceil(len(plaintext/bs))):
+        m = hashlib.sha256()
+        m.update(xor(key, iv + i.to_bytes(bs, byteorder='big')))
+        k = m.digest()
+        ciphertext += sxor(k, plaintext[bs*i:][:bs])
+
+def dec(ciphertext, key, iv):
+    return enc(ciphertext, key, iv)