Cryptographic Systems Used in the Romanian Countries between the 15th – 19th Centuries
By Cristina Flaut and Daniel Flaut
Asian Journal of Social Sciences & Humanities, Vol. 4:1 (2015)
Abstract: Situated in the southeast of Europe, Romanian Countries had an intense diplomatic activity, even if this was not recorded accordingly in documents of the day. This activity, as well as others made use of cryptography and cryptographic systems. Considering the scarcity of books devoted to this topic, the present paper is a survey regarding some of the encryption systems used in the Romanian Countries in the 15th-19th centuries, and will include a comparative approach between these and other encryption systems used in Europe at the same time.
Introduction: Classical ciphers can often be broken using some statistical information about the plain text, which means the frequency analysis of a letter in a text. After the discovery of frequency analysis allegedly by the Arab mathematician Al-Kindi in the 9th century, most of these ciphers became breakable until the development of the polyalphabetic ciphers. It is most likely that these ciphers were introduced by Leon Battista Alberti around 1467 and they used different ciphers for various parts of a message.
The execution of Mary Queen of Scots showed the vulnerability of the mono-alphabetic substitution cipher and the cryptographers had to find a new, stronger cipher that could trick the cryptanalysts. Leon Battista Alberti (1404-1472), Johannes Trithemius (1462-1516) (Brand, 1981) and Giovanni Battista Porta (1535- 1615) brought important contributions and the new found cipher became known as the Vigenère cipher after the name of the French diplomat Blaise de Vigenère (1523-1596), who gave it the final form. The latter published his work in Traicté des chiffres, ou secretes manieres d’escrire in 1586. That year, the cipher of Mary Queen of Scots had been broken. If Mary’s secretary had read the Vigenere’s treatise, he would have known about this new cipher. Although the Vigenere cipher was strong, it was rejected by the cipher secretaries since it was very hard to use at the time. During the following two centuries, this cipher was to remain largely neglected.
In the 17th century, the mono-alphabetic ciphers were used in several domains, but in diplomatic and military problems these ciphers were weak. The cryptanalysts of the time, who avoided the polyalphabetic ciphers due to their complexity, needed more secure ciphers and easier to use. One of the accepted ones was the homophonic substitution cipher in which each letter was replaced by a variety of substitutes whose number was proportional to the frequency of the letter. The homophonic substitution cipher is a monoalphabetic cipher.