I am sorry, but this is incorrect. Supposing by poly-alphabetic cipher you mean a substitution mechanism based on multiple alphabets (https://en.wikipedia.org/

I am sorry, but this is incorrect. Supposing by poly-alphabetic cipher you mean a substitution mechanism based on multiple alphabets (https://en.wikipedia.org/wiki/Polyalphabetic_cipher https://en.wikipedia.org/wiki/Polyalphabetic_cipher) (e.g. Enigma). This class does not provide information theoretic security. OTP does - it literally defined the notion. >> Modern cryptography is strong due to mainly a few key aspects, randomness which enables us to generate true or near true random keys, key exchange/distribution (electronic communications and various key exchange algorithms like DH) and non alphabetical plain text and keys. Maybe I am misunderstanding the statement you want to make here, but modern cryptography is strong because it is based on i) notion of information theoretic security ii) notion of computational security. The latter, upon which e.g. the Diffie-Hellman key exchange or RSA are built, states that distinguishing the output of the function from a particular distribution, can be used to solve problems we consider intractable (either on average or in the worst case). I am not sure to what you are referring to when stating: >> Modern encryption is fast and flexible but there are old ciphers that are just as strong when used correctly. To my knowledge that is not correct, but I am curious. (Shannon's analysis was the first rigorous treatment and bootstrapped the field.)