This document provides an overview of cryptology. It defines cryptology as the study of secret writings and notes that modern cryptology combines computer science and mathematics to encode information securely. It explains the basic concepts of encryption, where plaintext is encoded into ciphertext using an encryption key, and decryption, where the ciphertext is decoded back into plaintext using a decryption key. The document also gives an example of a basic letter substitution cipher and discusses cryptography, cryptanalysis, uses of cryptology in securing internet data and ATM transactions, and some limitations around the time required to create and break codes.