Classical Cryptography

Why
Classical Cryptography is important because it gives us a foundation to talk about the field of cryptography

What
Classical Cryptography consists of the following topics:
 * 1) Cryptosystems
 * 2) Substitution Ciphers
 * 3) Transposition Ciphers

Usefulness of Classical Ciphers
If the following two conditions are met, then any of these classical ciphers above can be considered to be useful and secure in the information theoretic sense.
 * 1) $$K >= M$$ or the key size is greater than or equal to the message size
 * 2) $$k \in_U K$$ is used once in each encryption only