Cryptography is a science that applies complex mathematics and logic to design strong encryption methods but also cryptography is an art. This art of hiding information from unauthorized eyes is with us from the beginning of the humanity and is related with the write invention.
The oldest known text containing one of the essential components of cryptography, a modification of the text, occurred around 2000 years BC, in the Egyptian town of Menet Khufu where the hieroglyphic inscriptions on the tomb of the nobleman Khnumhotep II were written with a number of unusual symbols to confuse or obscure the meaning of the inscriptions.
In 5 BC the Spartans, developed a cryptographic device to send and receive secret messages; this device, a cylinder called a Scytale, was in the possession of both the sender and the recipient of the message. To prepare the message, a narrow strip of parchment or leather, like a modern-day paper streamer, was wound around the Scytale and the message was written across it. Once unwound the tape displayed only a sequence of meaningless letters, it is transported to the receiver, and was re-wound onto a Scytale of exactly the same diameter. The code, produced by unwinding the tape, was a Transposition cypher, one where the letters remain the same but the order is changed. This is still the basis for many popular modern-day techniques.
Although the Greek writer Polyibus described a substitution technique, its first recorded use was by Julius Caesar. The messages were encoded by substituting the letter in the text by one that is three positions to the right. A became D, V became Y, etc. This is other major ingredient of these modern techniques that is the Additive/Substitution cypher.
Cryptography became more popular during the Middle Ages as encryption technologies became increasingly sophisticated based on the knowledge acquired during efforts to decrypt classical encryptions and the invention of new encryptions. The increased diplomatic activity during this time led to an increase in need to convey confidential information, which led to the frequent use of encryption.
The cipher used by Mary Queen of Scots to communicate with her collaborators, was known as a “nomenclator cipher”, and it included codes for replacing phrases in addition to replacing letters of the alphabet. These “codes” were listed in a “code book” or the “key” to the cipher, that was in the possession of both senders and recipients, and it made decrypting the cipher more difficult.
In an essay written in 1466, an Italian Leon Battista Alberti who is often called the ‘father of western cryptography’, described the construction of a cypher disk, founding the concept of Poly Alphabetic cyphers. They involve the use of two or more sets of encryption alphabets and have widely and frequently been used for decades. Although he had made the most important advance in cryptography in at least five hundred years, Blaise de Vigenère invented a strong final form of a polyalphabetic substitution cipher, such ciphers have been known as Vigenère ciphers or the Vigenere Square.
Vigenère introduce the concept of “key” that replace the simple substitution cyphers; the messages encrypted with a Vigenère cipher are completely different depending on the keys used, and even if a third party has acquired the conversion table, it is extremely difficult to decrypt a message without the key. The point here is that since there is no restriction on the number of characters or frequency that can be used as a key, an infinite number of keys can be conceived.
For example, if the key “OLYMPIC” is used to encrypt “GOLDMEDALIST”, the letters in the original text refer to the characters listed across the top of the table and the letters in the key refer to the characters on the left side of the table, thereby finding the encrypted message at their intersections.
For a considerable time afterwards this technique was believed to be unbreakable. There was however a weakness in this cypher waiting to be exploited because the cyphertext produced by this method was vulnerable to the yet undiscovered statistical attack.
During the 16th century a cipher that involved the use of a Polybius square was created in Japan. The method of preparing encrypted messages is described in the book on the art of warfare written by Sadayuki Usami, a strategist of Kenshin Uesugi, who was a warlord during the Sengoku (civil war) period in Japanese history. This Uesugi cipher involved the use of a table comprised of 48 Japanese syllabary phonetic characters inscribed on a grid of seven rows and seven columns, with each character represented by the numbers across the top of each row and column.
Probably in 1854, Charles Babbage, developed the method of statistical analysis by which he successfully decrypted messages encrypted by the Vigenere square. Unfortunately, due to his habit of not completing ‘the paperwork’, or possibly to protect the fact that because of his work Britain could decrypt Vigenere messages sent in the Crimea, this fact was not discovered until the twentieth century. The honour of developing the statistical attack technique and cracking Vigenere was to go to the Prussian Kasiski in 1863, this technique having since been termed the Kasiski Test.
This show us an idea how the war between the cryptographers and the cryptanalysts is old like the humanity itself.
Julian Bolivar-Galeno is an Information and Communications Technologies (ICT) Architect whose expertise is in telecommunications, security and embedded systems. He works in BolivarTech focused on decision making, leadership, management and execution of projects oriented to develop strong security algorithms, artificial intelligence (AI) research and its applicability to smart solutions at mobile and embedded technologies, always producing resilient and innovative applications.