The Woman Who Smashed Codes

by Jason Fagone

The strength of a cryptographic system usually has less to do with its design than with the way people tend to use it. Humans are the weak link. Instead of changing keys or passwords at regular intervals, we use the same ones over and over, for weeks or months or years. We repeat the same words (such as “secret”) at the start of multiple messages, or repeat entire messages multiple times, giving codebreakers a foothold. We choose key phrases that are easy to guess: words related to where we live or work, our occupation, or to whatever project we’re working on at the moment. A couple of human mistakes can bring the safest cryptographic system in the world to its knees.

Enigma was a straightforward idea expressed in a diabolical device. In the simplest sense, it was a box that cranked out poly-alphabetic ciphers. Remember the secret messages that eight-year-old Barbara Friedman sent her parents from summer camp? A=B, B=C, C=D. That’s a MASC, a mono-alphabetic substitution cipher. One cipher alphabet encrypts the whole message. Enigma was poly instead of mono, using multiple cipher alphabets per message. Poly-alphabetic ciphers date to the sixteenth century and can be written by hand with the aid of pre-printed grids of letters or sliding strips of paper. Instead, Enigma did the job with three or more rotating alphabet wheels connected to electrical wires. The wheels lived inside a box with a typewriter keyboard on the outside, the keys arranged in a familiar order, starting with Q W E R T Z U I O. Above the keyboard was a “lampboard” of the same twenty-six letters in the same order. When a writer pressed a key, such as Q, a different letter, perhaps Z, would illuminate on the lampboard—the cipher letter, lit by a small battery-powered bulb. Later, the recipient of the message, operating his own identically configured Enigma, would type Z, and Q would light up, decrypting the message letter by letter.