Foundations of Cryptography
Cryptography has been employed for keeping secrets since the time of Caesar. From the simplest ciphers of shifting letters, to mathematically provably secure ciphers of today, cryptography has progressed a long way. It also has widened to a number of uses and capabilities to fit an ever growing number of applications. Cryptography makes it possible to keep data secure over an insecure network. It also makes it possible to keep private data on your computer safe from prying eyes. Even car thieves can be foiled by crypto systems in your remote unlock system.
The basic idea of cryptography is to take a plaintext message, combine it with a key, and get ciphertext output. Once ciphertext is generated, its secrecy is not that important as long as the key is secret. Only those with the key to decrypt the message are able to read it. The process of encrypting plaintext messages is encryption. Getting the plaintext back from the ciphertext is decryption. The process of trying to break a cryptosystem is cryptanalysis.