Mac® Security Bible

13.1. File-Encryption Basics

This book won't turn you into an expert in cryptology, but because encryption can be so useful — in so many different ways — in keeping the data on your Mac safe, it's definitely worth knowing a few of the fundamentals of the process.

13.1.1. Encryption algorithms

An encryption algorithm, also known as a cipher, is a particular method for encrypting data — a sort of mathematical formula that takes the input (sometimes called cleartext), processes it using a secret piece of information (a key), and produces encrypted output (sometimes called ciphertext). Over the centuries, countless thousands of encryption algorithms have been developed, ranging from the trivially simple to the breathtakingly elaborate. In the modern computing world, you're likely to run into at least a half-dozen common ciphers considered especially well-suited for encrypting and decrypting data on your Mac!

Two factors influence how secure (resistant to being broken) an encryption algorithm is. First is the design of the algorithm itself. Some have weaknesses or design flaws that could enable an attacker to decrypt data even without knowing the key. The other factor is the complexity of the key. If you use the world's most complex and powerful cipher but give it a simple key, such as the word "cat," it becomes almost trivially easy for someone to figure out how to decrypt your data. The best results come from combining solid, reliable algorithms with long, random keys.

I could spend ...