Rabbi Menachem Rappaport, the Forgotten Inventor of “The Unbreakable Cipher” or the “Vigenère Cipher”

This lecture results from interdisciplinary research, conducted by Dr. Amit Kleinmann, Program of Cyber, Politics and Government Studies, Faculty of Social Sciences, Tel Aviv University, and Dr. Mor Altshuler, a scholar of Jewish Thought. The research is focused on Rabbi Avraham Menachem Ashkenazi Porto (Italy, 1520? -1596), one of the forefathers of the priestly family Rappa-Port; a Talmudist, physician, Occultist, and Renaissance polymath. A disciple of Rabbi Elia Levita, Rappa-Port supervised the printing of Rabbi Joseph Karo`s codex Shulchan Aruch in Venice in 1564-1565.

The lecture will concentrate on Rappa-Port`s contribution to modern cryptography by formulating the first polyalphabetic cipher, in which every letter in the plaintext can be substituted for any other letter of the alphabet, with an encryption key that determined the substitution order. Rappa-Port was never credited for his invention: his cipher was copied and published in Italian by cryptographer Giovan Battista Belaso in 1553. Two years later, Porto printed his cipher anonymously in Hebrew with the title Ẓofnat Pa`neaḥ along with his signed epistles to a Jewish dignitary, in which he explained the cipher`s uses. Eventually, his algorithm became famous by the generic name "Vigenère cipher" (1586) and was entitled "the unbreakable cipher," resisting attempts to break it for 300 years.

The lecture will open with the intellectual profile of Rappa-Port as "A Jew of the Renaissance," including his proficiency in the demonological theory of Johannes Trithemius (1462-1516), a German Benedictine abbot and a Christian Kabbalist, whose Polygraphia (1518) was the undeveloped source of Rappa-Port`s cipher. Then, attention will be given to poly-alphabetism in the ancient Book of Creation, which inspired Trithemius and Rappa-Port. Finally, the historical circumstances will be presented, especially the burning of the Talmud in Italy in 1553 and the shutdown of Hebrew printing houses, which prevented Rappa-Port from publishing his cipher in 1553.