"On the 2ROT13 Encryption Algorithm"(PDF). Prüfziffernberechnung in der Praxis. 25 September 2004. Archived(PDF) from the original on 15 April 2012. Retrieved 20 September 2007.
"On the 2ROT13 Encryption Algorithm"(PDF). Prüfziffernberechnung in der Praxis. 25 September 2004. Archived(PDF) from the original on 15 April 2012. Retrieved 20 September 2007.