 Communication Theory of Secrecy Systems by Claude Shannon

Primary text: www.4el.ch/crypto/bibliotheque/PDF/shannon1949.pdf

Cited passages: Sections 14–15, printed pp. 691–695, especially the discussion following Figure 7: random-cipher equivocation approaches zero sharply and defines an approximate unicity distance; section 15 lists corrections for actual ciphers. Published in Bell System Technical Journal 28(4), pp. 656–715, DOI 10.1002/j.1538-7305.1949.tb00928.x.