Introduction to cryptography

Source: Linux Focus

The origin of cryptography probably goes back to the very beginning of human existence, as people tried to learn how to communicate. They consequently had to find means to guarantee secrecy as part of their communications. However, the first deliberate use of technical methods to encipher messages may be attributed to the ancient Greeks, around 6 years BC: a stick, named "scytale" was used. The sender would roll a strip of paper around the stick and write his message longitudinally on it.

Then, he'd unfold the paper and send it over to the addressee. Decrypting the message without knowledge of the stick's width - acting here as a secret key - was meant to be impossible. Later, Roman armies used Caesar's cipher code to communicate (a three letter alphabet shift).

The next 19 centuries have been devoted to creating more or less clever experimental encipher techniques, whose security actually relied on how much trust user would grant them. During the 19th century, Kerchoffs wrote the principles of modern cryptography. One of those principles stated that security of a cryptographic system did not rely on the cryptographic process itself but on the key that was used.