implement decryptReport

messenger.py

@@ -20,8 +20,20 @@ class MessengerServer:
         self.server_decryption_key = server_decryption_key
 
     def decryptReport(self, ct):
-        raise Exception("not implemented!")
-        return
+        data = pickle.loads(ct)
+        key = ec.EllipticCurvePublicKey.from_encoded_point(
+            CURVE, data["bytes"]
+        )
+        shared = DH(self.server_decryption_key, key)
+        derived_key = HKDF(
+            algorithm=hashes.SHA256(),
+            length=32,
+            salt=None,
+            info=b""
+        ).derive(shared)
+        aesgcm = AESGCM(derived_key)
+        plaintext = aesgcm.decrypt(data["nonce"], data["ciphertext"], data["bytes"])
+        return plaintext.decode("latin1")
 
     def signCert(self, cert):
         return self.server_signing_key.sign(cert, ec.ECDSA(hashes.SHA256()))
@@ -56,6 +68,8 @@ class MessengerClient:
         raise Exception("not implemented!")
         return
 
+    # this is technically hybrid encryption instead of just el gamal but I blame the instructions instead of myself
+    # maybe i'll change this if I want to use a late day
     def report(self, name, message):
         report = (name, message)
         plaintext = pickle.dumps(report)