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An Independence Day look at encryption during the American Revolution

Every now and then at Hashed Out we like to take a look at historical examples of encryption. So far we’ve covered the Babington Plot and Antoine Rossignol’s Great Cipher. Today, on the United States of America’s Independence Day, we’re looking back at another historical example of encryption: the Culper Spy Ring and the Culper Code Book.

As you’re no doubt aware, encryption isn’t new at all. It’s been vaulted into the public’s consciousness recently because of its applications with technology and the internet, but encryption dates back thousands of years. The first known example was discovered in the form of Egyptian hieroglyphics on the wall of a tomb. Since then it’s progressed substantially.

Whereas historically encryption has been performed by an actual human being, nowadays our computers handle the function – it would take humans an entire lifetime to perform the prohibitively difficult mathematical functions that computers perform in just seconds. Provided a human could perform them at all. And that gap widens by the day. But rather than looking forward to our eventual demise at the hands of sentient machines, today let’s look back at encryption in a simpler time.

Back when people were still the ones doing the enciphering and a compromised private key could very literally cost you your head. Today we discuss the Culper Spy Ring.

Let’s hash it out.

Let’s dust off our powdered wigs and head back to 1778

Before we really get going on the historical encryption stuff we kind of need to give some background and context. I’m going to go out on a limb and say that if the American school system barely teaches this stuff – it’s probably not any better represented in international curriculums.

If you ask most Americans, they’ll rattle off the revolutionary war, something about founding fathers, they may toss the declaration of independence in there, but if you mention the British occupation of New York their face is going to glaze over.

And frankly, this is neither the time, nor the place to really go into a full explanation of the events that unfolded during the American revolution. So, we’re going to be fairly cursory, and try to stick to the main points.

The American Revolution officially began in 1775. We get hung up on the July 4, 1776 date because it’s the day that the Declaration of Independence was ratified, but revolution had already been underway well over a year by that point. And you can look back as far as 1773 when the tea partiers Lipton-ed the Boston harbor if you want to point to where America’s defiance of the British royal crown officially kicked off. Or even the massacre that occurred on Boston’s King Street three years earlier as the official genesis of the hostilities.

And the revolution lasted until 1783.

The Culper Ring operated during the last five years of the Revolutionary War and was instrumental in ending it. Yet, it was unknown by historians for over 140 years.

Molding the Culper Ring

The Americans had been using spies since before the revolution even began, but traditionally it had been officers. That was problematic because these men were too easy to recognize.

George Washington, who was leading the American forces and directing the spies found this out the hard way when Nathan Hale was caught spying in New York and executed. Before he was hung Hale is alleged to have given some of the most badass last words in history:

I only regret that I have but one life to lose for my country. -Nathan Hale

After Hale’s death, Washington realized he was going to need to start using civilians to spy on the British.

Now, remember earlier I mentioned the British occupation of New York? That was for a reason.

Shortly after the Declaration of Independence – about a month and a half later on August 22, 1776 – the British sailed into New York with 32,000 troops and took it over for the next seven years. One does not simply declare independence from the British.

Anyway, Washington knew he was going to need to use civilians to surveil the British in New York if he wanted to have any prayer of staying a step ahead of them. And thus, the Culper spy ring was formed.

At the top of the spy network were the two men that facilitated it. Neither of them actually did any of the spying, they just organized the information and made sure it got to Washington. Their names were Caleb Brewster, who was the first to approach Washington about offering his assistance, and Major Benjamin Tallmadge, who was Washington’s spymaster.

The man they chose to do the actual spying was named Abraham Woodhull from Long Island, whom Washington dubbed “Samuel Culper” after Culpeper County, Virginia. Woodhull had a sister that lived in the city, which offered a pretext for him to be there.

Initially, Woodhull would do some spying and then head back to Long Island to pass a message to Brewster, who would cross the Long Island Sound and deliver the intelligence to Tallmadge in Connecticut.

Then things started to scale, couriers became involved to speed up the passing of intelligence. Woodhull, operating as Culper, provided information about British troop movements, naval construction, British plans and activities in New York and Connecticut. Even a plot to counterfeit Continental Currency to drive down its value.

Eventually he got spooked though, fearing British reprisal should he ever be discovered.

And they were getting close. The British had already intercepted a message that referred to a C_____ operating out of New York, and they already knew Tallmadge was Washington’s spymaster. So, they raided his camp and found even more incriminating information. Around this same time, on the advice of a criminal, a British Colonel paid a visit to Woodhull in Setauket, Long Island – the spy ring’s hub – and, finding Woodhull was in New York City at the time, beat the tar out of his father.

Woodhull was done going to the city after that. So, he offered up a replacement: Robert Townsend. Townsend would become Samuel Culper Jr.

Given that Townsend was already involved in business there, his presence was less suspicious. Woodhull stayed in Setauket and reorganized the network. This is where it really took off. Hundreds of civilians were enlisted as spies and the network started using a complex system of ciphertext and dead drops to handle communication.

The Culper Ring ended up being incredibly successful. When Benedict Arnold – who up to that point was more famous for his eggs – was planning to give West Point to the British, Washington knew ahead of time because of the Culper spy ring.

When the French arrived in Rhode Island in 1780, the Culper Ring’s intelligence prevented a British ambush and potentially saved the Franco-American alliance.

The ring can even be credited with saving Washington’s life when it uncovered British plans to assassinate America’s eventual first president as he met with the French.

The Culper Spy Ring continued to operate until the end of the Revolutionary War and achieved far more than any other intelligence network – American, British or French – during that time. It was an early example of a clandestine cell system. Members were only known by an assigned number and didn’t know who else was involved. Townsend’s identity as Culper Jr. was unknown to almost all but Tallmadge, Brewster and the couriers. Even Washington (#711) didn’t know everyone that served in the Culper ring.

In fact, nobody knew about them until the 1930s when historians were examining old letters from the Townsend estate and discovered his secret identity as Culper Jr. From there historians began to unravel the Culper Ring’s elaborate web by matching handwriting with other historical documents from the Washington collection. To this day not all the members have been identified.

The Culper Code Book

Ok, now let’s talk about historical encryption. We’ve discussed symmetric or private key encryption before. In order for the text to be encrypted (or perhaps more appropriately, enciphered) and decrypted (deciphered) the sender and recipient both needed to have the same private key.

The key could either be duplicated or passed back and forth.

After losing Hale, Washington realized he needed to start using civilians. After nearly losing Woodhull and Tallmadge, he realized he needed to start using encryption. Well, maybe not Washington himself, but someone figured it would be smart to start using it. The British had indeed figured out the identity of the first Samuel Culper, care would need to be taken to ensure no more slip-ups occurred.

And thus, the Culper Code Book was created. A collection of 763 numbers. 710 represented specific words. The other 53 numbers were for names and places. The code book was developed by Tallmadge, who went by the alias John Bolton.

Notable Names

Number Name Number Name 711 George Washington 719 Frederick North 712 Henry Clinton 720 George Germain 713 William Tryon 721 John Bolton/Benjamin Tallmadge 714 Robert Erskine 722 Samuel Culper/Abraham Woodhull 715 John Vaughan 723 Samuel Culper Jr./Robert Townsend 716 Beverley Robinson 724 Austin Roe 717 John Brown 725 Caleb Brewster 718 Thomas Garth 726 James Rivington

Notable Places

Number Location Number Location 727 New York 745 England 728 Long Island 746 London 729 Setauket 747 Portsmouth 730 Kingsbridge 748 Plymouth 731 Bergen 749 Ireland 732 Staten Island 750 Corke 733 Boston 751 Scotland 734 Rhode Island 752 West Indies 735 Connecticut 753 East Indies 736 New Jersey 754 Gibraltar 737 Pennsylvania 755 France 738 Maryland 756 Spain 739 Virginia 757 Scotland 740 North Carolina 758 Portugal 741 South Carolina 759 Denmark 742 Georgia 760 Russia 743 Quebec 761 Germany 744 Halifax 762 Hanover

The number 763 stood for “Headquarters.”

In addition to the 763 numbered words, names and places, there was also a table for the alphabet and for numbers

Alphabet

Letter Replacement Letter Replacement A e N p B f O q C g P r D h Q k E i R l F j S u G a T v H b U w I c V x J d W y K o X z L m Y s M n Z t

Numbers

Number Replacement Number Replacement 1 e 6 m 2 f 7 n 3 g 8 o 4 i 9 q 5 k 0 u

Before we get into how this all worked, I like that as you start to look at the alphabet here it starts out looking like it’s just a simple shift cipher, where each letter is pushed forward by a set number of places in the alphabet. That’s actually what Caesar’s cipher was, a simple shift cipher – though if you ever want to sound impressive at a party it’s also accurate to call it a mono-alphabetic shift cipher with a modulus of 26… I wouldn’t lead with that though.

Anyway, I could almost picture Washington reviewing Tallmadge’s work and looking up when he get to the alphabet at the end, “Ben, did you just shift all the letters five places?”

“…yes.”

“Don’t you think they’re going to figure that out?”

And then Tallmadge grudgingly took it back to the drawing board and mixed it up a little more. It looks like he also did the same thing with the letters, he just got rid of the H, J and P.

Anyway, let’s look at how this worked.

How did the Culper Code Book work?

Obviously, the English language consists of far more than just 763 words, which is why they included an alphabet and some letters at the end of the code book.

In this encryption scheme, the code book functions as the private key. Ideally the word you want to use is represented by a number, if it’s not – maybe a synonym is?

Failing that, the alphabet would be used to encipher the word. Now, you’re probably asking how both letters and numbers can share the same symbol – because you are very intuitive and you noticed that right away.

Letters were meant to be underlined once, numbers underlined twice, with a period after them. There are also little symbols that could be left beside the numbered words to indicate tense, moods or numbers.

All said, it was actually a fairly sophisticated cipher for the time, though it likely would have been crackable if subjected to frequency analysis and other cryptoanalytic techniques. Maybe not contemporaneously, but definitely today.

Still, this code book helped win America its independence from the Royal crown, which was a major blow to the British empire. The two countries would renew hostilities again for the War of 1812 when the US invaded Canada and the British invaded the US again. That was resolved in 1814. And then things cooled off between the countries over the next 40 years with the Monroe Doctrine condemning any future European efforts to colonize the Western world while agreeing to stay out of their affairs in Europe.

And it’s all because of encryption… Ok, that’s not true. But encryption did play a vital role in the American Revolution and its war for independence.

In fact, as the world debates banning end-to-end encryption, it’s worth keeping in mind that America’s founding fathers once used it themselves. In fact, were it not for encryption the French would have been ambushed before they could gain a foothold in Rhode Island, Benedict Arnold would’ve turned over control of West Point and the Hudson River to the British, and George Washington could’ve been assassinated.

If any of those had happened, who knows whether or not America wins the war.

As always, feel free to leave any comments or questions below…