In 1948 he created a test that he thought could prove that he could communicate with living people after his death. One way of testing this was to ask dying people to write a message that would be sealed, then ask a medium to try to contact the deceased for the message. The weakness in this was that the medium might have been shown the message before the seance, so he enciphered it using keywords he refused to divulge. The ciphertext was "BTYRR OOFLH KCDXK FWPCZ KTADR GFHKA HTYXO ALZUP PYPVF AYMMF SDLR UVUB".