CRYPTANALYTIG PROPERTIES OF SHORT SUBSTITUTION CIPHERS
Roland Anderson · Cryptologia · 1989
Evidence is presented which tends to indicate that the possible interpretations of very short simple substitution cipher are few in number. If “side information” is available, that is, if the analyst can correctly recognize topic, style, content, or completeness of thought, then simple substitution ciphers shorter in length than the unicity distance can readily be solved. Such results provide a theoretical basis for cryptanalytic methods which begin initially with very short segments of text.