Much of the underlying technology that makes the rest of computer security work involves cryptography. Cryptography has been around for eons, and it will be around long after we leave planet Earth for other hospitable planets. Personally, cryptography is the computer security genre that I love the most, even though after nearly three decades of being a crypto‐hobbyist I don’t consider myself a cryptography expert.

In the digital world, cryptography is the use of a series of binary 1s and 0s to encrypt or verify other digital content. Cryptography involves using mathematical formulas (called *ciphers*) along with those 1s and 0s (called *cryptographic keys*) to prevent unauthorized people from seeing private content or to prove the identify or validity of another person or some unadulterated content.

The simplest encryption example I can think of is where some plaintext (non‐encrypted) content is converted to an encrypted representation by moving the alphabet of each involved character by one place (for example A becomes B, B becomes C, C becomes D, and so on, until Z becomes A). Thus, the word FROG would become GSPH. The decryptor could reverse the process to reveal the original plaintext content. In this example, the cipher (it’s almost silly to call it one) is the math, which in this case is + or – (addition or subtraction), and the key is 1. As simple as this example is, hundreds of years of secret messages (and cereal box decoder rings) ...

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