A Brief History Of Cryptology: Cryptography and Cryptanalysis In Practice

Cryptology is the study of establishing a channel for secret communications (cryptography) and breaking secret communication channels of enemies (cryptanalysis).

Cryptography focuses on ensuring that messages from a sender can only be read by the intended recipient(s). A sender’s original message is transformed from plain text into coded text (encrypted) before being sent to the recipient. Only the recipient holds the information (cipher) required to transform the coded text back into plain text (decryption) and read the original message.

Everyone else— that is, anyone without the cipher— can only see the encrypted message, which is completely unintelligible. To read the message, these eavesdroppers would need to use cryptanalysis to crack the code and discover the cipher based on the encrypted messages.

The importance of cryptology can’t be overstated. Cryptology has decided the outcome of numerous military conflicts throughout history. In today’s world, this field of study facilitates information security for the entire internet. This article looks at how cryptology has evolved from ancient times to the present day. We’ll cover some of the most influential techniques, people, and events that have helped advance the practice of cryptology to the modern, digital era.

Cryptology And The Cipher

To understand how cryptology has evolved over time, it’s important to comprehend the role of the cipher. A cipher is basically a set of specific instructions for encryption and decryption. With a low-quality cipher, it’s easy for anyone (including unintended recipients) to decrypt coded messages. With a high-quality cipher, the intended sender and intended recipient are able to securely exchange secret communications. Adversaries will be unable to break the code of a high-quality cipher.

As the field of cryptology advanced, cryptographers sought to develop ciphers that are impossible for cryptanalysts to understand. In ancient times, ciphers were very basic patterns that could be broken by humans in a manner of minutes. Today, ciphers are complex algorithms that usually require decades of research, along with the assistance of supercomputers, to break. Now, let’s look at the strengths and weaknesses of several different ciphers used throughout history.

Early History Of Cryptology

Cryptology isn’t a new field of study. Encrypted messages are thought to have been first used in the Old Kingdom of Egypt as early as 1900 BC. While no one knows exactly when cryptanalysis began, it’s possible that people have been trying to “crack the code” for as long as encryption has existed. Here are a few of the most important examples of cryptology throughout pre-modern and early modern history.

Scytale

The scytale is a very simple cipher tool used in ancient Greece, especially by the Spartans. No one knows exactly when the scytale was invented. In the 7th century BC, a poet named Archilochus was the first known person to mention the scytale in writing.

The scytale consists of a piece of parchment wrapped around a rod or baton. The parchment includes a message written using a transposition cipher, which simply rearranges the order of plain text. If the parchment was unwrapped on a baton of the wrong circumference, the message was unintelligible. When wrapped around an appropriately-sized baton, the message becomes readable. In that sense, the cipher was merely the correct circumference of the baton.

The Scytale was mainly used as a fast, simple way to send messages to soldiers in the battlefield. It wasn’t all that practical because encrypted messages were also easy for enemy soldiers to read.

Caesar Cipher

Caesar Cipher is a basic and widely-known cipher. It’s named after Julius Caesar, who is said to have used this cipher in his private correspondence in the 1st Century BC. Caesar Cipher is a type of monoalphabetic substitution cipher, which uses a cipher alphabet for encryption and decryption. A cipher alphabet is just the same as a plain text alphabet, but letters are rotated a specified number of places to the left or to the right.

For example, an encrypted message might use a cipher alphabet that rotates the plain text alphabet five letters to the right.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

F G H I J K L M N O P Q R S T U V W X Y Z A B C D E

In this example, “Cryptology” would be written as “Hwduytqtld”. The recipient would rotate the cipher alphabet five places to the right to decrypt the message. Much like the Scytale, anyone who intercepted this message could eventually guess the pattern necessary to decrypt the message. A Caesar Cipher would require at most 26 attempts at decryption.

Seed words 13-16 for the KMD Treasure Chest listed in order: rival base spirit strike

A Manuscript on Deciphering Cryptographic Message

“A Manuscript on Deciphering Cryptographic Message” was written by al-Kindi during the 9th Century AD. This is the earliest known description of cryptanalysis. al-Kindi’s work focused on frequency analysis, which is the study of the frequency of letters or groups of letters used in encrypted messages. Some people regard al-Kindi’s manuscript as the most influential contribution to cryptanalysis prior to World War II.

al-Qalqashandi's Encyclopedia

In the 15th Century, al-Qalqashandi published a 14-volume encyclopedia called Subh al-A'sha. A section on cryptology was credited to a cryptologist named al-Durayhim. The list of ciphers in this work included substitution ciphers and transposition ciphers. The encyclopedia introduced the first known homophonic substitution cipher, which uses multiple substitutions for each letter of the alphabet. It also cited al-Durayhim’s cryptanalysis work, including the first known tables of letter frequencies and sets of letters which couldn’t occur together in one word.

Cryptology In The Renaissance

During the Italian Renaissance, which spanned the 15th and 16th centuries, cryptology gained widespread attention. During this period, Italian city-states were competing against one another for power. Francesco I Gonzaga, who ruled the northern Italian city of Mantua, used cryptography for secret communications. When sending a letter to the king of Hungary in 1401, Gonzaga used a homophone substitution cipher. Cryptanalysis also became a highly regarded skill. During the 1500s, Giovanni Soro, a talented cryptanalyst, was renowned for his ability to decrypt messages written in Latin, Italian, French, and Spanish.

What’s even more interesting is that the role of cryptology greatly expanded in society. Previously, it was mainly limited to government or military correspondence. In the Italian Renaissance, bankers and merchants also started using encrypted messages in their business communications.

Technological Advances Fuel Interest In Cryptology

Throughout the early history of cryptology, not much changed, as cryptography and cryptanalysis had both existed for centuries. The techniques used for both only became slightly more advanced. One of the biggest limitations was that communication remained extraordinarily slow. Sending an encrypted message (or any message) from Point A to Point B could take weeks or months. Beginning in the 19th Century, advances in electronic communication technologies would drastically increase the relevance of cryptology.

Morse Code And The Telegraph

In 1837, Samuel Morse developed and patented the electric telegraph. This device allowed for the transmission of information over long distances through coded signals. At one telegraph station, an operator tapped on a switch and spelled out messages in Morse code that could be sent around the world. At another telegraph station, an operator would listen for these sounds and write down the corresponding messages.

In 1865, the Morse system became the standard for international communication. This standardization meant that Morse code wasn’t a form of encryption in itself. However, it created the foundation necessary for high-speed encrypted communication. Ordinary messages, called telegrams, could be encrypted using any number of ciphers that were only known by certain senders and recipients. One example is the Fractionated Morse Cipher.

WWI And The Zimmerman Telegram

Telegrams played a crucial role in wartime communications, especially during World War I. For a majority of WWI, the Central Powers (Germany, Austria-Hungary, Ottoman Empire and Bulgaria) were winning. On January 19, 1917, Germany proposed a military alliance with Mexico via an encrypted telegram, which is now known as the Zimmerman Telegram. British intelligence intercepted and decrypted the message. They later shared this information with US officials. The United States entered WWI on April 6, 1917. The United States and the Entente Powers officially claimed victory on November 11, 1918. Thus, many historians believe that cryptanalysis changed the outcome of WWI.

WWII And The Enigma Machine

German engineer Arthur Scherbius invented the Enigma machine at the end of WWI. The device looked like an oversized typewriter but was actually much more powerful. The Enigma machine itself was an algorithm that supported automated encryption, which made it easier to send and receive secret messages. This device was used by several countries, most notably Germany before and during WWII. Compared to the Zimmerman Telegram, messages encrypted with the Enigma machine proved to be much more difficult to crack with cryptanalysis.

During WWII, Polish mathematicians successfully discovered how to decrypt German military messages, but this didn’t help in all scenarios. That’s because German officials were able to use the Enigma machine to change their ciphers on a daily basis, which meant successful cryptanalysis had to be extremely fast to actually be useful.

British cryptanalysts Alan Turing and Gordon Welchman developed a machine known as the Bombe. Starting in 1940, this device was used to quickly calculate all possible cipher combinations and easily break Enigma machine encryption. These decrypted messages were listed under the code name “Ultra.” The Bombe helped automate much of the cryptanalysis workload and enabled the Allied Powers to defeat the Axis Powers in WWII.

The Era Of Modern Cryptology

Cryptology was a clear beneficiary of the communications improvements in the 19th century and first half of the 20th. Despite technological advancements, the cat-and-mouse game still favored cryptanalysis over cryptography. Encryption could be broken with relative ease. After WWII, research efforts by cryptographers and mathematicians would eventually lead to breakthroughs in cipher security. As a result, cryptanalysis has been exponentially more difficult ever since.

Public Key Cryptography

From the invention of the Scytale all the way through the Enigma machine, it was always difficult to securely distribute the cipher. If the cipher was compromised, it became useless and could even be used as a counter-weapon. This is known as the key distribution problem: in order to establish secure and secret communications problems, the cipher would need to be exchanged in an unencrypted format. This created a major vulnerability for even the most advanced cryptographic techniques.

To improve the security of encryption, cryptographers began to develop a new system called a public-key cipher, better known as public key cryptography. In this new cryptosystem, there would be no need for private key exchange. Instead, each individual would have their own private key and their own public key, which would correspond directly with one another. The public key could be shared publicly and is used to encrypt messages. The private key is kept secret and is used to decrypt any messages encrypted with the paired public key.

In 1969, researchers at the United Kingdom’s GCHQ, an intelligence agency, first proposed the idea for public key cryptography. Their solution aimed to solve the key distribution problem through asymmetric encryption. They proposed the use of a cryptographic algorithm that required two keys: a private key and a public key. Formulating this idea into a functional algorithm was a monumental feat that GCHQ cryptographers were never able to accomplish.

The Diffie-Hellman key exchange, published in 1976, brought the idea of public key cryptography closer to reality. This algorithm used a private key and public key but still required two users to derive a shared private key. It was never necessary to exchange the private key over an insecure channel, as each party derived the shared private key independently. However, Diffie-Hellman key exchange still fell short of allowing every person to have one private key with which they could decrypt all messages encrypted for them and them alone.

The release of the RSA algorithm in 1977 finally introduced a practical public key algorithm that didn’t require private key exchange or the derivation of a shared private key. RSA also introduced a digital signature scheme to allow recipients to verify the identity of the sender as well as the authenticity of messages with almost total certainty. The combination of public/private key pairs and digital signatures ultimately facilitated the development of several new generations of algorithms in the 1990s and 2000s. These breakthroughs led to the emergence of new technologies powered by public key cryptography— PDF signing, email, the SSL protocol, and distributed ledger technology, to name just a few examples.

Hashing Algorithms

Research on hashing algorithms, also known as cryptographic hash functions, began in the 1970s. Previously, cryptography had only focused on sending (encrypting) and receiving (decrypting) messages, which always involved two or more people. During the 1990s, hashing algorithms became more advanced and thus gained increased importance in cryptography.

Hashing algorithms introduced one-way encryption. Once a message has been run through a hashing algorithm to create an output, nobody can decrypt it to learn the input. This unique characteristic enabled hashing algorithms to set the foundation for data security, especially with the advent of the internet. For example, online payment data and password data both rely upon the ability of hashing algorithms to defend against cryptanalysis.

Modern Cryptanalysis

Just as modern cryptography relies upon powerful computers to maintain encryption, modern cryptanalysis depends upon supercomputers to break encryption. There are a number of strategies that have been used to increase the capabilities of cryptanalysis. However, with the emergence of modern cryptography, cryptanalysis heavily relies upon the success or failure of brute-force techniques— that is, guessing all possible inputs until a correct answer is found.

Cryptanalysis efforts have yielded some results, but progress has been very slow in the era of modern cryptology. For example, the original RSA algorithm was broken by brute-force in 1991. Fortunately, real-world applications had already moved on to more secure implementations that weren’t vulnerable to cryptanalysis.

For most public key cryptosystems, cryptanalysis can be mitigated simply by using longer public/private key pairs. For hashing algorithms, cryptanalysis can be mitigated by producing longer outputs. These incremental security measures are relatively easy for cryptographers to implement. On the other side, cryptanalysis becomes substantially more difficult.

Post-Quantum Cryptography

It’s certainly possible to argue that a new era of cryptology has already begun: post-quantum cryptography. Although quantum computers are still theoretical, they are expected to become functional in the coming decades. They will be able to perform cryptanalysis exponentially faster than computers are capable of today. Many public key algorithms, digital signature schemes, and hashing algorithms in use today are at risk of being broken by quantum computing. That’s why cryptographers are focused on building quantum-resistant algorithms.

In 2016, the National Institute for Standards and Technology (NIST), an agency of the US Department of Commerce, started a research initiative called Post-Quantum Cryptography. The focus of this initiative is to advance the standardization of one or more quantum-resistant algorithms. In January 2019, NIST announced Round 2 candidates for public key encryption algorithms and digital signature algorithms.

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