Mathematical Foundation for Agrippa’s Encryption Code (Item #D4) (Facsimile Images)
Chapter five, “Congruences and Residues,” of E.M. Wright and G.H. Hardy’s An Introduction to the Theory of Numbers provides an explanation and summary of Euler’s fuction, the mathematical basis for programming the encryption code on the Agrippa diskette that made William Gibson’s poem seem to “disappear” after it it has scrolled up the screen once.
See also the programmer’s letter on the encryption code.