The Evolution of Cryptography

The term cryptography originates from the Greek words "kryptos" and "graphien," translating to hidden writing, which is a practice that has been evolving for thousands of years. Cryptography and cryptology are terms often used interchangeably, but they hold distinct meanings in the domain of secure communication. Cryptology is the broad study that encompasses both cryptography and cryptanalysis. Cryptography involves the creation of codes and ciphers to protect information, rendering it unreadable to anyone except those possessing the key to decode it. On the other hand, cryptanalysis is the art of breaking these codes and ciphers, deciphering the encrypted information without the key. Historically, cryptology has been a part of human communication and warfare since ancient civilizations like the Greeks and Romans, who employed various methods to keep their messages secret. Cryptography, as a subset of this field, has evolved from simple techniques like the Caesar cipher to the sophisticated algorithms used in digital security today.

The earliest known use of cryptography was discovered in an inscription from around 1900 BC in the tomb of the nobleman Khnumhotep II in Egypt. This inscription featured unusual hieroglyphic symbols, not to hide the message but to present it in a more dignified form. While the inscription wasn’t secret writing, it did transform the original text, making it the oldest known example of this kind. Similarly, clay tablets from Mesopotamia, dated around 1500 BC, were discovered to encrypt a craftsman's recipe for pottery glaze, highlighting the early commercial use of cryptographic techniques.

Fast forward to around 100 BC, Julius Caesar was known to use a form of encryption to convey secret messages to his army generals posted on the war front. This substitution cipher, known as the Caesar cipher, is perhaps the most mentioned historic cipher in academic literature. In a substitution cipher, each character of the plain text (the message that needs to be encrypted) is substituted by another character to form the cipher text (the encrypted message). The variant used by Caesar was a shift by three ciphers. Each character was shifted by three places, so the character 'A' was replaced by 'D,' 'B' was replaced by 'E,' and so on. The characters would wrap around at the end, so 'X' would be replaced by 'A.'

It is easy to see that such ciphers depend on the secrecy of the system and not on the encryption key. Once the system is known, these encrypted messages can easily be decrypted. In fact, substitution ciphers can be broken by using the frequency of letters in the language.

Medieval Cryptography

In medieval times, cryptographic techniques advanced significantly, particularly among the Arabs, who were the first to systematically document cryptanalytic methods. Al-Khalil (717–786) wrote the "Book of Cryptographic Messages," which included the first use of permutations and combinations to list all possible Arabic words with and without vowels. However, the most notable advancement came from Al-Kindi, an Arab mathematician who invented the frequency analysis technique around AD 800. This technique proved to be the most significant cryptanalytic breakthrough until World War II. Al-Kindi's book, "Risalah fi Istikhraj al-Mu'amma" (Manuscript for the Deciphering Cryptographic Messages), described various cryptanalytic techniques, including frequency analysis, which involved examining the frequency of letters and combinations in a language to break monoalphabetic substitution ciphers. This period also saw significant cryptographic experimentation in early medieval England, where substitution ciphers were used for enciphering notes, riddles, and colophons.

In his work "On Deciphering Cryptographic Messages," al-Kindi provided the first documented methods of cryptanalysis and frequency analysis.

During the 16th century, Vigenere designed a cipher that was supposedly the first cipher which used an encryption key. In one of his ciphers, the encryption key was repeated multiple times spanning the entire message, and then the cipher text was produced by adding the message character with the key character modulo 26. (Modulo, or mod, is a mathematical expression in which you calculate the remainder of a division when one number is divided by another.) As with the Caesar cipher, Vigenere's cipher can also easily be broken; however, Vigenere's cipher brought the very idea of introducing encryption keys into the picture, though it was poorly executed. Comparing this to Caesar cipher, the secrecy of the message depends on the secrecy of the encryption key, rather than the secrecy of the system.

Vigenere Cypher

At the start of the 19th century when everything became electric, Hebern designed an electro-mechanical contraption which was called the Hebern rotor machine. It uses a single rotor, in which the secret key is embedded in a rotating disc. The key encoded a substitution table and each key press from the keyboard resulted in the output of cipher text. This also rotated the disc by one notch and a different table would then be used for the next plain text character. This was again broken by using letter frequencies.

The Enigma machine was invented by German engineer Arthur Scherbius at the end of World War I, and was heavily used by the German forces during the Second World War. The Enigma machine used three or four or even more rotors. The rotors rotate at different rates as you type on the keyboard and output appropriate letters of cipher text. In this case the key was the initial setting of the rotors.

The Enigma machine's cipher was eventually broken by Poland and the technology was later transferred to the British cryptographers who designed a means for obtaining the daily key. During World War I, another notable cryptographic event was the interception and decryption of the Zimmermann Telegram by British intelligence, which played a crucial role in bringing the United States into the war.

Up to the Second World War, most of the work on cryptography was for military purposes, usually used to hide secret military information. However, cryptography attracted commercial attention post-war, with businesses trying to secure their data from competitors.

In the early 1970's, IBM realized that their customers were demanding some form of encryption, so they formed a "crypto group" spearheaded by Horst-Feistel. They designed a cipher called Lucifer to enhance electronic banking. In 1973, the National Bureau of Standards (now called NIST) in the US put out a request for proposals for a block cipher which would later become a national standard. They had obviously realized that they were buying a lot of commercial products without any good crypto support. Lucifer was eventually accepted and was called DES or the Data Encryption Standard. In 1997, and in the following years, DES was broken by an exhaustive search attack. The main problem with DES was the small size of the encryption key. As computing power increased it became easy to brute force all different combinations of the key to obtain a possible plain text message.

In 1997, NIST again put out a request for proposal for a new block cipher. It received 50 submissions. In 2000, it accepted Rijndael, and christened it as AES or the Advanced Encryption Standard. Today AES is a widely accepted standard used for symmetric encryption.

In recent times, advancements in quantum computers have led us to think about Post Quantum Cryptography. In 2016 NIST declared a “call for proposals” seeking public help in designing quantum resistant algorithms which could help us “withstand the assault of a future quantum computer”. In 2020 NIST announced four finalists for the same.

To conclude, history teaches us:

The secrecy of your message should always depend on the secrecy of the key, and not on the secrecy of the encryption system. (This is known as Kerckhoffs's principle.)

Related to the above, always use ciphers which have been publicly reviewed and have been established as a standard. Using "secret crypto" is bad, because just like the Caesar cipher, once the system is known, all messages can be decrypted. For example, if your key is compromised, an attacker could access your messages; however, if the attacker can compromise the crypto system itself, they can obtain the plain text of every message (not just for a single person) encrypted by that system.

Blockchain and Modern Cryptography

The modern era of cryptography is defined by the advent of blockchain technology. Cryptography is the fundamental backbone of blockchain, ensuring the security and integrity of transactions. Blockchain relies on advanced cryptographic algorithms to secure data, create digital signatures, and ensure the immutability of records. This technology has revolutionized various industries, enabling the rise of cryptocurrencies like Bitcoin and Ethereum.

Blockchain technology is not exactly a new concept. Almost forty years ago, cryptographer David Chaum proposed a blockchain-like protocol in his 1982 dissertation entitled "Computer Systems Established, Maintained, and Trusted by Mutually Suspicious Groups." This pioneering work laid the foundation for the development of blockchain as we know it today. In 1991, Stuart Haber and W. Scott Stornetta further developed the concept of a cryptographically secured chain of blocks, which addressed issues related to document timestamps and the prevention of backdating.

These early works formed the bedrock of modern blockchain technology, which was later refined and popularized by Satoshi Nakamoto in the 2008 Bitcoin white paper. Nakamoto's work introduced a decentralized ledger system that combined cryptographic techniques with consensus mechanisms to create a secure, transparent, and immutable digital currency.

The evolution of cryptography has been marked by significant milestones, from the simple substitution ciphers of ancient times to the complex algorithms of modern blockchain technology. Each era has brought new challenges and innovations, reflecting the ever-changing landscape of information security. Understanding this history is crucial for appreciating the advancements in cryptographic practices and their impact on contemporary technologies like blockchain. As we move forward, the principles of cryptography will continue to shape the future of secure communication and data protection.

Sources:

DigiCert. "The History of Cryptography." DigiCert Blog, [Link].
"A Brief History of Cryptography." Red Hat Blog, [Link].
"The History of the Blockchain and Bitcoin." Freeman Law, [Link].

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