Cryptographie indéchiffrable (English: Indecipherable Cryptography) (subtitle: basée sur de nouvelles combinaisons rationelles (based on new rational combinations)) is a French book on cryptography written by Émile Victor Théodore Myszkowski, a retired French Army colonel, and published in 1902. His book described a cipher that the author had invented and claimed (incorrectly) was "undecipherable" (i.e. secure against unauthorised attempts to read it). It was based on a form of repeated-key transposition.
References
See also Books on cryptography Transposition cipher List of ciphers