Cyber Security: Cryptography - Hidden Messages

Cryptography is a specialised area of mathematics concerned with protecting information so that it can be transmitted and received securely even when there is a risk that a hostile third party might intercept or modify the data.

     

The secret of keeping secrets
There have been many applications of cryptography throughout history, ranging from simple ciphers used by Julius Caesar to send military orders to his generals, to the more sophisticated medieval ciphers that withstood most attacks until the late 19th century and the famous Enigma codes of World War II.

The development of computers in the 20th century allowed for far more complex means of encryption. Computers could perform:

• the mathematical operations that underpin all cryptography
• much more complex mathematics than could be reasonably expected of a human
• much faster than a human
• on much more data than a human could handle.

Any data that could be represented in binary format, i.e. using 0s and 1s, can be encrypted by a computer. It is not an exaggeration to say that encryption makes much of the modern world possible. Some commonplace applications for cryptography include:

     

• secure banking and payments systems – cryptography ensures your money is safe when it is transferred between accounts, issued at ATMs or used to shop online
• protecting conversations made over mobile telephones
• safeguarding wireless networks that give access to the internet
• securing files on hard disks and memory sticks
• authenticating electronic documents
• electronic voting
• securing media files such as music or movies from piracy, where it is known as Digital Rights Management (DRM).

Plaintext and ciphertext
As in previous weeks, there is some terminology we need to introduce:

• plaintext – information that can be directly read by humans or a machine (this article is an example of plaintext). Plaintext is a historic term pre-dating computers, when encryption was only used for hardcopy text, nowadays it is associated with many formats including music, movies and computer programs
• ciphertext – the encrypted data
• a cipher – the mathematics (or algorithm) responsible for turning plaintext into ciphertext and reverting ciphertext to plaintext. (You might also see the word ‘code’ used. There is a technical difference between the two but it need not concern us now.)
• encryption – the process of converting plaintext to ciphertext (occasionally you may see it called ‘encipherment’)
• decryption – the process of reverting ciphertext to plaintext (occasionally ‘decipherment’).