Added proof-of-concept decoder in Python 3

src/decode.py

@@ -0,0 +1,19 @@
+#!/usr/bin/env python3
+
+import pysodium
+import base64
+import sys
+
+assert(len(sys.argv) > 1)
+
+input = sys.argv[1]
+ciphertext = base64.b64decode(input)
+
+with open('./recipient_sk.raw', 'rb') as f:
+	sk = f.read()
+
+with open('./recipient_pk.raw', 'rb') as f:
+	pk = f.read()
+
+cleartext = pysodium.crypto_box_seal_open(ciphertext, pk, sk)
+print(cleartext)