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The history of codes and cryptography is a fascinating topic that spans thousands of years and involves many different methods and technologies. I have wanted to write on this topic for quite some time now but couldn’t complete it due to other projects at hand. Many people on individual basis and even companies use cryptographic techniques for various reasons from protecting sensitive data and preventing espionage to enabling the creation and exchange of cryptocurrency and other digital assets. But many people have little to no idea about the evolution of codes and cryptographic systems. In this piece, we shall briefly overview some of the main phases and milestones in the development of cryptology, the science of making and breaking codes.

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Ancient Ciphers and Early Encryption Techniques

Ancient ciphers and early encryption techniques are methods of transforming messages or information in such a way that only authorized parties can access them. They usually involve replacing or rearranging the letters or symbols of the original message with a secret key or algorithm. Here are some examples of ancient ciphers and early encryption techniques:

The Caesar Shift Cipher

The Caesar cipher, employed by Julius Caesar and his army during the 1st century BC, served as a means to encrypt military and official messages. Operating as a simple substitution cipher, it involved replacing each letter in the message with another letter positioned a fixed number of places away in the alphabet. For instance, with a shift of 3, ‘A’ would be substituted with ‘D’, ‘B’ with ‘E’, and so forth. The key for this cipher represented the number of positions to shift, encompassing values ranging from 1 to 25. To decipher the message, the recipient needed knowledge of the key to revert the letters to their original positions. However, the Caesar cipher was susceptible to frequency analysis, a method involving the tabulation of letter occurrences in the ciphertext and comparing them against the expected frequencies in the language, thus rendering it relatively easy to break.

The Scytale Cipher

The Spartans and other ancient Greeks utilized a cipher during the 7th century BC for the encryption of military and political messages. This particular cipher operated as a transposition cipher, whereby the arrangement of letters in the message was altered based on a concealed pattern. The pattern, in this case, was determined through the utilization of a cylindrical rod known as a scytale. To encrypt the message, the sender would encircle a strip of parchment or leather around the scytale and proceed to inscribe the message along its length. Subsequently, the strip would be unwrapped and dispatched to the intended recipient. For decryption, the recipient would require a scytale possessing an identical diameter to rewrap the strip around it and decipher the concealed message. This cipher’s security was compromised, as its vulnerability lay in attempting various diameters of rods until the message became intelligible, rendering it relatively easy to break.

The Steganography

Steganography, distinct from a cipher, represents a technique employed to conceal messages in plain sight by disguising them as something else. Its origins can be traced back to ancient times, and it has found utility across a range of endeavors encompassing espionage, propaganda, and art. Several examples of steganography include inscribing a message on a shaved head, allowing the hair to regrow and obscure the hidden text, utilizing invisible ink or microdots to convey information, and embedding messages within different mediums, such as texts, images, audio, or video files. If executed adeptly, steganography can prove challenging to detect; nevertheless, it can be exposed through meticulous scrutiny or by subjecting the medium to careful examination or analysis.

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The Renaissance and Early Modern Cryptography

The Renaissance and early modern period witnessed a flourishing of cryptography as a result of political, religious, and scientific developments. Cryptography became more sophisticated, diverse, and widespread, as well as more subject to cryptanalysis and code-breaking. Here are some aspects and examples of cryptography in this era:

The rise of diplomatic cryptography

During the Renaissance, a notable transformation occurred in the realm of diplomacy, paving the way for the establishment of a modern system characterized by permanent embassies, the formulation of international law, and multilateral negotiations among autonomous states. Given the crucial need for secure communication between ambassadors and their respective home governments, as well as among allies and adversaries, the significance of cryptography as an indispensable tool for diplomats became apparent. Cryptography served a dual purpose, enabling diplomats to safeguard their confidential information while simultaneously providing a means to engage in covert intelligence gathering, influencing public sentiment, and monitoring their rivals’ activities. As diplomatic relations evolved, cryptography emerged as an essential component in the arsenal of tools employed by diplomats to navigate the intricate web of international affairs during the Renaissance.

Here’re a few examples of diplomatic cryptography are:

• The Vigenère cipher, a polyalphabetic substitution cipher that was considered unbreakable for centuries. It was invented by Giovan Battista Bellaso in 1553 and improved by Blaise de Vigenère in 1586. It was widely used by European diplomats until the 19th century.
• The Babington Plot, a conspiracy to assassinate Queen Elizabeth I of England and replace her with Mary, Queen of Scots in 1586. The plot was exposed by Sir Francis Walsingham, Elizabeth’s spymaster, who intercepted and deciphered the letters between the plotters using a nomenclator, a combination of symbols and code words.
• The Great Cipher, a complex substitution cipher that was used by the kings of France from Louis XIV to Louis XVI. It was invented by Antoine and Bonaventure Rossignol in 1645 and remained unsolved until 1890.

One component of a customary nomenclator employed during the era of Louis XIV, 1690. Wikimedia Commons Public Domain Image.

The role of cryptography in religion and science during the Renaissance

Within the backdrop of the Renaissance, a period characterized by profound intellectual and societal transformations, religious conflicts like the Protestant Reformation and the Catholic Counter-Reformation took center stage. Simultaneously, the era bore witness to groundbreaking scientific advancements and methodologies, including the revolutionary Copernican heliocentric model and the Baconian induction. In the middle of these developments, cryptography emerged as a significant factor influencing both religious and scientific domains. Cryptography served as a means to express dissent, preserve orthodoxy, and facilitate the clandestine transmission of knowledge. Furthermore, it became a subject of scholarly inquiry and experimentation for esteemed scholars and natural philosophers of the time. Cryptography thus acquired a dual role, influencing and being influenced by the intellectual currents that shaped the Renaissance era.

Some examples of cryptography in religion and science are:

• The Trithemius cipher, a progressive polyalphabetic substitution cipher that was invented by Johannes Trithemius, a German abbot and occultist, in 1508. It was disguised as a book on magic called Steganographia, which claimed to teach how to communicate with angels using hidden messages in texts.
• The Baconian cipher, a biliteral substitution cipher that was devised by Francis Bacon, an English philosopher and scientist, in 1605. It used two different typefaces or fonts to encode messages within other texts. Bacon also proposed a method of hiding messages in musical notes or knots.
• The Newtonian cipher, a numerical substitution cipher that was used by Isaac Newton, an English physicist and mathematician, to encrypt his private notes on alchemy and theology. He assigned numbers to the letters of the alphabet according to their order or frequency and wrote them in groups of five.

Photo by K. Mitch Hodge on Unsplash

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The Enigma Machine and World War II

The Enigma machine and World War II are closely related, as the Enigma was a cipher machine used by Nazi Germany to encrypt and decrypt messages for military and diplomatic purposes. The Enigma was considered to be very secure and reliable, but it was eventually broken by the Allies, who used the intelligence gained from reading the German messages to gain an advantage in the war.

The Enigma machine

The Enigma machine, conceived by German engineer Arthur Scherbius in 1918 and patented in 1923, emerged as a remarkable electro-mechanical apparatus consisting of several components. Comprising a keyboard, lampboard, plugboard, and a set of rotors, it enabled the encryption and decryption of messages.

Photo by Christian Lendl on Unsplash

Users would input plaintext or ciphertext through the keyboard, and the corresponding encrypted or decrypted letters would be displayed on the lampboard. The plugboard facilitated additional permutations of letters, while the rotors, altered with each keystroke, modified the electrical connections between the keyboard and lampboard. The Enigma machine boasted an extensive array of potential settings, rendering the key challenging to guess or crack via brute-force methods. These settings involved the selection and order of rotors, initial rotor positions, and the plugboard configuration. To maintain security, these settings were altered daily or even more frequently, using secret key lists that were distributed to operators in advance. Although initially intended for commercial purposes, the Enigma machine swiftly gained traction among various military and government entities worldwide, most notably the Nazi regime in Germany, who employed it extensively before and during World War II.

World War II

World War II, a global conflict spanning from 1939 to 1945, witnessed the engagement of two opposing alliances: the Axis powers and the Allied powers. The devastating war led to vast casualties, widespread destruction, and profound socio-political transformations.

Cryptography played a pivotal role during this period as both sides employed various encryption and decryption techniques to secure their communications and gather intelligence on their adversaries.

Among these methods, the Enigma machine held paramount importance for Nazi Germany, serving as a device to encode critical messages across all branches of the German military. The initial breakthrough in cracking the Enigma code came in 1932 when Polish mathematicians developed techniques and machines to decipher it. They subsequently shared their achievements with British and French intelligence prior to the outbreak of the war. In 1939, Britain established the clandestine code-breaking unit Ultra at Bletchley Park, led by mathematician Alan Turing and a team of experts. Building upon the Polish methods, they refined decryption processes and devised new machines, such as the Bombe, to decipher Enigma messages on a larger scale. The successful decryption of the Enigma code provided the Allies with a pivotal advantage in numerous battles and campaigns, including the Battle of Britain, the Battle of the Atlantic, and the pivotal D-Day invasion. It also allowed for vigilant monitoring of German movements, plans, and intentions. Estimates from historians suggest that the breaking of the Enigma code potentially shortened the war by two to four years, resulting in the preservation of millions of lives.

Photo by Mauro Sbicego on Unsplash

The Digital Age and Public-Key Cryptography

The digital age and public-key cryptography are interrelated, as the advent of digital technologies and the internet created new challenges and opportunities for cryptography.

Public-key cryptography, aka asymmetric cryptography, is a cryptographic field that employs a pair of interconnected keys, namely a public key and a private key, for the purpose of encrypting and decrypting messages.

Public-key cryptography revolutionized the field by allowing secure communication between parties who have no prior knowledge or trust of each other, using mathematical techniques such as asymmetric encryption and digital signatures.

The digital age

The digital age is the period of history characterized by the widespread use of digital technologies, such as computers, the internet, mobile devices, and social media. The digital age began in the late 20th century and continues to the present day. This age has brought many benefits and challenges for cryptography. On one hand, it has enabled faster, cheaper, and more accessible encryption and decryption of data, as well as new applications and domains for cryptography, such as e-commerce, online banking, cloud computing, cryptocurrency, and blockchain.

On the other hand, it has also increased the risks and threats of cyberattacks, hacking, surveillance, identity theft, and data breaches. It has also increased the demand and complexity of cryptography. As more data is generated, stored, transmitted, and processed online, there is a greater need for protecting its confidentiality, integrity, authenticity, and availability. As more users and devices are connected to the internet, there is a greater challenge for distributing and managing cryptographic keys securely.

Public-key cryptography

Public-key cryptography was invented in 1976 by Whitfield Diffie and Martin Hellman in their seminal paper “New Directions in Cryptography”. They proposed a method of key exchange that allowed two parties to establish a shared secret key over an insecure channel without any prior communication or trust. This method is known as the Diffie-Hellman key exchange.

This type of cryptography that uses pairs of related keys:

a public key that can be openly distributed without compromising security, and

a private key that should be kept under secrecy by the owner of the key

The keys are generated with cryptographic algorithms based on mathematical problems called one-way functions, which are easy to compute in one direction but hard to reverse.

Public-key cryptography has two main functions: encryption and digital signatures. Encryption is the process of transforming a message into an unreadable form using a key. Digital signatures are the process of creating a unique code that can verify the identity of the sender and the integrity of the message using a key. Anyone with a public key can encrypt a message for a specific recipient who has the corresponding private key. The decryption of the message can only be performed by the intended recipient using their private key.

Consider this example, Alice can send Bob an encrypted message using Bob’s public key that only Bob can decrypt with his private key. In public-key digital signatures, anyone with a private key can sign a message with their private key to create a signature. The authenticity of the signature and its association with the signer can be verified by anyone possessing the corresponding public key and confirming if it matches the message. For example, Alice can sign a message with her private key to create a signature that Bob can verify with Alice’s public key.

This type of cryptography was further developed by Ronald Rivest, Adi Shamir, and Leonard Adleman in 1977 when they created the RSA algorithm, which is one of the most widely used public-key encryption and digital signature schemes today. RSA stands for Rivest-Shamir-Adleman, the initials of its inventors.

Ronald Rivest, Adi Shamir, & Leonard Adleman, 1977. Photographed by: Unknown. Source: National Cryptographic Foundation

Quantum Cryptography: A New Era of Encryption

A new era of encryption phrase that describes the use of quantum physics to create and secure cryptographic systems that are theoretically immune to conventional attacks.

Quantum cryptography exploits the properties of quantum mechanics, such as superposition, entanglement, and uncertainty, to perform tasks that are impossible or infeasible with classical cryptography.

Quantum key distribution

Quantum key distribution (QKD) stands as the most extensively explored and implemented approach within the realm of quantum cryptography. Serving as a technique, QKD enables two parties, commonly referred to as Alice and Bob, to establish a shared secret key over an insecure communication channel, including fiber-optic cables or free space, devoid of any prior communication or established trust. QKD capitalizes on the principle that quantum states, such as photons, cannot be replicated or measured without perturbation. Thus, any potential eavesdropper, often denoted as Eve, who endeavors to intercept or tamper with the quantum signals will inevitably introduce errors or irregularities, which can be detected by Alice and Bob. Through the implementation of suitable protocols and error correction techniques, Alice and Bob can generate a key that boasts provable security and randomness. This key can subsequently be utilized for encrypting and decrypting messages using conventional symmetric-key algorithms like AES or DES.

The notable advantage of QKD lies in its ability to securely distribute keys, addressing a prominent vulnerability within classical cryptography. Additionally, QKD facilitates the frequent updating of keys, thereby amplifying the security and freshness of the encryption process. The conceptualization of QKD originated from independent proposals by Stephen Wiesner in 1970 and Charles Bennett and Gilles Brassard in 1984. The first experimental demonstration of QKD occurred in 1990, conducted by Bennett and John Smolin. Since then, QKD has been further developed and tested across diverse settings, including metropolitan networks, satellite links, and underwater channels.

Stephen Wiesner, 1988. Public Domain Image. Wikimedia Commons.

Quantum-resistant cryptography

Quantum-resistant cryptography, also known as post-quantum cryptography or quantum-proof cryptography, is a branch of classical cryptography that aims to create encryption methods that cannot be broken by quantum computers. Quantum computers are hypothetical machines that can exploit quantum phenomena to perform certain computations faster than classical computers.

QRC is motivated by the fact that some of the most widely used public-key algorithms, such as RSA and ECC, are based on mathematical problems that are hard to solve with classical computers but easy to solve with quantum computers. For example, Shor’s algorithm is a quantum algorithm that can factor large numbers efficiently, which would break RSA encryption. Similarly, Grover’s algorithm is a quantum algorithm that can search unsorted databases faster than classical algorithms, which would reduce the security of symmetric-key algorithms. The objective is to develop novel public-key algorithms that rely on mathematical problems posing challenges for both classical and quantum computers in terms of solving them. Some of the candidates for quantum-resistant cryptography are based on lattice problems, code problems, multivariate problems, hash-based problems, or supersingular elliptic curve problems. These algorithms are currently being evaluated and standardized by various organizations, such as NIST and ETSI.

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Cryptography has evolved from simple manual methods to complex mechanized and digital systems, driven by the needs and demands of communication, security, and privacy. It has also played a very crucial role in many historical events (the Babington plot, for example), such as wars, revolutions, and discoveries, as well as in many modern applications, such as e-commerce, online banking, and cryptocurrency. It’s not only a practical tool, but also a scientific and mathematical discipline that explores the limits and possibilities of information theory, computation, and quantum physics. It is constantly changing and most certainly evolving, as new threats and opportunities emerge in the digital age.

By：Sunny Labh Link：https://www.cantorsparadise.com/the-history-of-codes-and-cryptography-from-caesar-cipher-to-quantum-encryption-262992255320