THE EVOLUTION OF CRYPTOGRAPHY THROUGHOUT HISTORY
There have been many examples of application of cryptography in history, and it changed throughout the years. According to Gustavus Simmons from Britannica Online, “there have been three well-defined phases in the history of cryptology.” The first was the period of manual cryptography, starting with the origins of the subject in antiquity and continuing through World War I. Throughout this phase cryptography was limited by the complexity of what a code clerk could reasonably do aided by simple mnemonic devices. As a result, ciphers were limited to at most a few pages in size, i.e., to only a few thousands of characters. General principles for both cryptography and cryptanalysis were known, but the security that could be achieved was always limited by what could be done manually. Most systems could be cryptanalyzed, therefore, given sufficient ciphertext and effort. One way to think of this phase is that any cryptography scheme devised during those two millennia could have equally well been used by the ancients if they had known of it.
The second phase, the mechanization of cryptography, began shortly after World War I and continues even today. The applicable technology involved either telephone and telegraph communications (employing punched paper tape, telephone switches, and relays) or calculating machines such as the Brunsvigas, Marchants, Facits, and Friedens (employing gears, sprockets, ratchets, pawls, and cams). This resulted in the rotor machines used by all participants in World War II. These machines could realize far more complex operations than were feasible manually and, more importantly, they could encrypt and decrypt faster and with less chance of error. The secure size of ciphers grew accordingly, so that tens or even hundreds of thousands of characters were feasible. The switch from electromechanical devices to electronic ones accelerated this trend. To illustrate the progress that was made in only eight decades, in 1999 the U.S. government designed and fabricated a single silicon chip implementation of the Data Encryption Standard (DES) with a demonstrated throughput of 6.7 billion bits (6.7 gigabits) per second. The Advanced Encryption Standard (AES) can be implemented in a single silicon chip to handle 1010 bits per second (10 gigabits per second) on an Internet backbone circuit. In a few seconds of operation, trillions of bits of cipher can be processed, compared with the tens of bits per second possible with the first mechanized cipher machines. By the end of the 20th century the volume of ciphertext that had to be dealt with on a single communications channel had increased nearly a billionfold, and it continues to increase at an ever-expanding rate.
The third phase, dating only to the last two decades of the 20th century, marked the most radical change of all—the dramatic extension of cryptology to the information age: digital signatures, authentication, shared or distributed capabilities to exercise cryptologic functions, and so on. It is tempting to equate this phase with the appearance of public-key cryptography, but that is too narrow a view. Cryptology’s third phase was the inevitable consequence of having to devise ways for electronic information to perform all of the functions that had historically been done with the aid of tangible documents.
The third phase, dating only to the last two decades of the 20th century, marked the most radical change of all—the dramatic extension of cryptology to the information age: digital signatures, authentication, shared or distributed capabilities to exercise cryptologic functions, and so on. It is tempting to equate this phase with the appearance of public-key cryptography, but that is too narrow a view. Cryptology’s third phase was the inevitable consequence of having to devise ways for electronic information to perform all of the functions that had historically been done with the aid of tangible documents.