Klein, стр. 3 “Vernam had invented the unbreakable cipher: “one-time tape” (OTT) for on-line TTY encryption. In 1919. he was granted a patent, perhaps one of the most important in the history of cryptography.” Klein, Melville, Securing Record Communications: The TSEC/KW-26(PDF), Архивирано из оригинала 10. 10. 2012. г., Приступљено 12. 4. 2012CS1 одржавање: Неподобан URL (веза)