The Ancient Roots of Cryptography
Primitive cryptographic techniques are known to have existed in ancient times, and most early civilizations appear to have used cryptography to some degree. Symbol replacement, the most basic form of cryptography, appears in both ancient Egyptian and Mesopotamian writings. The earliest known example of this type of cryptography was found in the tomb of an Egyptian noble named Khnumhotep II, who lived approximately 3,900 years ago.
The purpose of symbol replacement in the Knhumhotep inscription was not to conceal information but to enhance its linguistic appeal. The earliest known example of cryptography being used to protect sensitive information occurred around 3,500 years ago when a Mesopotamian scribe employed cryptography to conceal a formula for pottery glaze, which was used on clay tablets.
By later periods of antiquity, cryptography was widely used to protect important military information, a purpose that it still serves to this day. In the Greek city-state of Sparta, messages were encrypted by being written on parchment laid over a cylinder of a particular size, making the message undecipherable until it was wrapped around a similar cylinder by the recipient. Likewise, spies in ancient India are known to have used coded messages as early as the 2nd century BC.
Perhaps the most advanced cryptography in the ancient world was achieved by the Romans. A prominent example of Roman cryptography, known as the Caesar cipher, involved shifting the letters of an encrypted message by a certain number of places down the Latin alphabet. Knowing this system and the number of places to shift the letters, a recipient could successfully decode the otherwise illegible message.
Developments in the Middle Ages and Renaissance
Throughout the Middle Ages, cryptography became increasingly important, but substitution ciphers, of which the Caesar cipher is one example, remained the standard. Cryptanalysis, the science by which codes and ciphers are cracked, began to catch up to the still relatively primitive science of cryptography. Al-Kindi, a noted Arab mathematician, developed a technique known as frequency analysis around 800 AD that rendered substitution ciphers vulnerable to decryption. For the first time, people attempting to decipher encrypted messages gained access to a systematic method for doing so, making it necessary for cryptography to advance even further in order to remain useful.
In 1465, Leone Alberti developed the polyalphabetic cipher, which is considered the solution against Al-Kindi's frequency analysis technique. In a polyalphabetic cipher, a message is encoded using two distinct alphabets. One is the alphabet in which the original message is written, while the second is an entirely different alphabet in which the message appears after being encoded. Combined with traditional substitution ciphers, polyalphabetic ciphers greatly increased the security of encoded information. Unless a reader knew the alphabet in which the message had originally been written, the frequency analysis technique was of no use.
New methods of encoding information were also developed in the Renaissance period, including a popular early method of binary encoding invented by the noted polymath Sir Francis Bacon in 1623.
Advances in More Recent Centuries
The science of cryptography continued to advance progressively throughout the centuries. A major breakthrough in cryptography was described, though perhaps never built, by Thomas Jefferson in the 1790s. His invention, known as the cipher wheel, consisted of 36 rings of letters on moving wheels that could be used to achieve complex encoding. This concept was so advanced that it would serve as the basis for American military cryptography until as late as the Second World War.
World War II would also see the perfect example of analog cryptography, known as the Enigma machine. Like the wheel cipher, this device, employed by the Axis powers, used rotating wheels to encode a message, making it virtually impossible to read without another Enigma. Early computer technology was eventually used to help break the Enigma cipher, and the successful decryption of Enigma messages is still considered to be a critical component of the eventual Allied victory.
Cryptography in the Computer Age
With the rise of computers, cryptography became vastly more advanced than it was in the analog era. 128-bit mathematical encryption, far stronger than any ancient or medieval cipher, is now the standard for many sensitive devices and computer systems. Beginning in 1990, an entirely new form of cryptography, dubbed quantum cryptography, was under development by computer scientists hoping to once again elevate the level of protection offered by modern encryption.