I recently finished “High: Confessions of an International Drug Smuggler“. The author, Brian O’dea, is a former (and now reformed) drug smuggler and addict who pulled off a few very large smuggling operations. In one of his largest ones he tried to bring in huge quantities of drugs from Asia via boat without being picked up by the feds who had been tipped off to his activities by an informant. They also needed to communicate with boats as far away as the South China sea and Alaska from the US mainland. They decided to use Single-sideband radio, which was used by licensed amateurs. They set up an antenna in a campground powered by a mobile home. It had the power they needed for communications, but the government knew about single-sideband, and was constantly monitoring for people using it for illicit purposes.

Since it was 1985, they didn’t have access to modern cryptography. To avoid the feds, they needed something which not only encoded their information, but also sounded innocuous. Here’s what they did. They all bought copies of Websters dictionary. When they wanted to send a sentence, they looked up each word in the dictionary, noted the page number, and the entry it was on the page. If the word appeared on page 795, and was the 23rd word on the page then he would call the ship (or the home base in the other direction) and ask them to check part number 795-23. Doing this over and over again any eavesdropper would think it was just a ship requesting information on a list of parts.

Analyzing this, it is actually surprisingly good. At first I assumed that because it’s a basic substitution cipher, usually the easiest type of cipher to break, it would crumble quickly. However, substitution ciphers are usually broken because they don’t hide the distribution of letters, and their distribution can be easily matched to the distribution of English letters. In this case they’re not substituting letters, but words. There are only 26 letters in English, but far more words. Given the extremely small amount of ciphertext, it is unlikely that a proper distribution could ever have been discovered. While a straight substitution cipher has very little entropy, and the ciphertext is still going to be highly structured, the limited amount of ciphertext would make cryptanalysis very hard. Someone trying to attack the system would probably only break it if they managed to get a person to talk or captured a boat and noticed the dictionary lying conspicuously close to the radio equipment.

Tags: brian o'dea, cryptography, dictionary, drugs, smuggling

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