Octet String to integer and integer to octet string.

Signed-off-by: HeshamTB <hishaminv@gmail.com>

OAEP.py

@@ -0,0 +1,22 @@
+#From: https://stackoverflow.com/questions/39964383/implementation-of-i2osp-and-os2ip
+
+def i2osp(x, xLen):
+        if x >= 256**xLen:
+            raise ValueError("integer too large")
+        digits = []
+
+        while x:
+            digits.append(int(x % 256))
+            x //= 256
+        for i in range(xLen - len(digits)):
+            digits.append(0)
+        return digits[::-1]
+
+def os2ip(X):
+        xLen = len(X)
+        X = X[::-1]
+        x = 0
+        for i in range(xLen):
+            x += X[i] * 256**i
+        return x
+

encodetest.py

@@ -38,3 +38,14 @@ print(sig_enc)
 sig_un = en.decrypt(sig_enc,d,n)
 print(sig_un)
 print(key)
+
+import OAEP
+
+key = en.generateKeys("encode-test", 2048)
+x = int(en.encrypt("test message", (key[en.N], key[en.E])))
+print(x)
+encoded_msg = OAEP.i2osp(x, key[en.N].bit_length())
+print(encoded_msg)
+
+decoded = OAEP.os2ip(encoded_msg)
+print(decoded)