The OTP, or One-Time Pad, also known as the Vernam cipher, is, according to the NSA, “perhaps one of the most important in the history of cryptography.”  If executed correctly, it provides uncrackable encryption.  It has an interesting and storied history, dating back to the 1880s, when Frank Miller, a Yale graduate,  invented the idea of the OTP.  Communication was expensive and difficult in the age of telegrams, and few messages were easily encrypted.  Miller laid out his solution to this problem in the preface of a codebook used to reduce the cost of telegrams by shortening messages. His theory used a pen-and-paper system, relying on printed keys to be safely distributed to both parties.  Experts theorize that he probably didn’t even realize its potential, and his discovery was soon forgotten.  In fact, Miller’s codebook was only unearthed in 2011.

The better known inventor of the OTP was Gilbert Vernam, who lent his name to the Vernam cipher.  An AT&T engineer, he developed and, in 1919 patented a system for cryptography using punched tapes to store a randomized key.   Still, though, the parameters of the OTP had not been defined.  When Captain Joseph Maubourgne saw Vernam’s machine, he laid out many of the conditions necessary for an OTP today, such as using a truly randomized key which would be destroyed after one use.  Though this version garnered some use from the commercial sector and the military, it also went largely unnoticed.

The OTP finally gained some traction in the 1920s when three German cryptologists, Kunze, Schauffler, and Langlotz, independently discovered it.  They returned to the pen and paper system, similar to what Miller had proposed.  The random sequences of numbers would be printed on small pads of paper which would be ripped off and destroyed after use, giving the system the name One Time Pad.  Today, this format is most common in espionage operations, in which a small pad of paper can be easily and discreetly distributed to both parties.  The German government adopted the system in 1923.

The most famous item in cryptography used in World War II was probably the Enigma machine.  Its intricacies were seemingly uncrackable, but it was famously decoded after much time and effort.  The Polish Cipher Bureau reconstructed an Enigma machine and used it to decrypt German communications for much of the 1930’s, finally sharing with Britain in 1939. Had the Germans used a properly implemented OTP system, it would have been completely uncrackable, and the outcome of WWII could have been entirely different.

With the more practical system in place, many other sources began to utilize this encryption technique.  In the 1940s, Claude Shannon proved mathematically that if all of the requirements of an OTP are met( truly random numbers, disposal after one use, etc.), it is uncrackable.  This strengthened the OTP’s reputation, as well as making it the only truly secure cryptography technique.  In this same decade, the United States government began the Venona project in an attempt  to crack the code that the Soviets had been using to send messages during the war.  Had the Soviets followed the requirements of an OTP, the U.S. would never have been able to decode the messages; however, some pages of keys were reused, and later into the project some partially undestroyed keys were found.  The repetition of keys was especially important; while OTPs are completely uncrackable with constantly unique random keys, once a key is reused it becomes susceptible to cryptanalysis.  The decoding of these messages led to the arrest of the Rosenbergs, who had been giving away atomic bomb secrets.

The SIGSALY was Another interesting World War II era device based on the principles of the OTP.  The SIGSALY was a voice encrypter, which recorded the voice, compressed the frequencies of the messages, and then added in a track of background noise which made the original message impossible to hear.  Only two copies of this background noise were made, which is where the similarity to the OTP comes in.  These copies were put onto records, one of which was distributed to either end of the system.  Then, the background noise could be removed, the frequencies decrypted, and the original message received.  Since there were only the two discs of background noise, decryption by other sources was practically impossible.  The machine worked well, but it was expensive and time-consuming, and was only used a few times.

In 2012, an encrypted message from WWII was discovered in a highly unlikely place.  A British man found the skeleton of a carrier pigeon in his chimney, with a message still intact and attached.  After analyzing the message, authorities still cannot begin to crack it, and have deduced that the message was encoded using an OTP.  The codebook was likely destroyed after the message was not received, demonstrating the lasting reliability of the OTP.

During the Cold War, the concept of OTP was used with One Time Tape (OTT), similar to the Vernam Cipher.  After the Cuban Missile Crisis, both American and Soviet leaders recognized the importance of a direct and secure means of contact between the two countries.  To resolve this, they built the Washington-Moscow Hotline, utilizing the OTT, which used teleprinters and identical tapes to relay messages securely.  The intended message would be typed in both English and Russian, transmitted across the ocean, and deciphered.  Because of the difficulty of securely supplying the tape, the hotline has since changed form.  The OTP has been used by many spy organizations because of its practicality even without a computer.  Number pads were small and easily concealable, and often printed on flash paper or some other easily destroyed substance.  With the key, the decryption is also relatively simple, so less human error would be likely to occur.

The One Time Pad Today

The One Time Pad is currently used in asymmetric network encryption. This is commonly referred to as a pseudo One Time Pad harkening back to it’s origins. In simple terms, each side of the communication has a known calculation or cipher it uses to generate the Pad of random information. To make sure it is unique, key pairs are used. In short, the identical Pads are generated on each end of the communication. This allows both sides to generate the Pad without having to transmit it across the network working in similar fashion to the German World War II Enigma machine. While this technique is sound and, implemented correctly, provides a high degree of confidence that data can not be decrypted, the fact remains that anything that is calculated can be easily solved for. The NSA leaks of 2013 taught us that data over the internet is being recorded and, even if a crack did not exist at the time of the recording, the recording could be cracked later when an exploit is found or advances in technology make a “brute force” crack possible. With the increase in processing cores, the reduction of power consumption and the mitigation of semiconductor heat generation combined with the large bit word size and vector computing used in GPU’s, the ability to brute force crack most asymmetric encryption rapidly approaching, if not already here.

This problem is twofold: 1) data transmission recording needs to be stopped and 2) a real, truly random One Time Pad needs to be used in network encryption. Using a real, symmetric OTP in a network has been something of a “holy grail” or “unicorn” problem until now. Introspective Networks has discovered a method to deliver the pad from one side to the other, securely creating a Streaming One Time Pad (patent #8,995,652 aka STOP – Streaming Transmission One-time-pad Protocol). This technique combines a real, truly random One Time Pad with something akin to frequency hopping (a technique used to disguise radio transmissions) in the network. This allows the pad to be sent across the network securely and, by “port hopping,” the risk of recording is fundamentally removed. STOP represents a seminal technology that changes the rules for how data is secured in the network using a proven method of encryption – the One Time Pad.

As a truly indecipherable means of encryption, the One Time Pad is an extremely important invention.  From its humble beginnings as a mere mention within the introduction of a telegram codebook, the OTP has grown to become a ubiquitous part of cryptography.  When used correctly, it’s the perfect way to send secure messages, but if all its rules are not followed, it becomes susceptible to decryption. From Vernam to Mauborgne to Shannon, the OTP has been influenced by many people, each of whom added their own bit of expertise to the concept.  The fact that a correctly executed OTP message still protects its secret decades later only speaks to the durability of the system. Its many applications, such as OTT and SIGSALY speak for its versatility.  The path to the OTP was not without hurdles, of course, but from usage by espionage organizations to governments to international communication it has improved substantially, cementing its title as a truly unbreakable encryption method.  However, the OTP’s history is not yet fully written, and the next chapter begins with Introspective Networks’ patented STOP technology.