http://bitmsgdy44b7kwtsjbsbvl4r2j7gqpjx6kiqrvbh56phc6pyai5uzmyd.onion/index.php?title=Encryption&action=history
Calculate MAC' with HMACSHA256, using key_m as salt and IV + R + cipher text as data. Compare MAC with MAC'. If not equal, decryption will fail. Decrypt the cipher text with AES-256-CBC, using IV as initialization vector, key_e as decryption key and the cipher text as payload.