async def prep(wallet_handle, my_vk, their_vk, msg):
    msg = bytes(msg, "utf-8")
    encrypted = await crypto.auth_crypt(wallet_handle, my_vk, their_vk, msg)
    # encrypted = await crypto.anon_crypt(their_vk, msg)
    print('encrypted = %s' % repr(encrypted))
    with open('message.dat', 'wb') as f:
        f.write(encrypted)
    print('prepping %s' % msg)