Uruguayan Cryptographic Carpet

Juan José Cabezas
Instituto de Computación, Facultad de Ingeniería, Universidad de la República, Montevideo, Uruguay

Joachim von zur Gathen
B-IT, Universität Bonn, Germany

Jorge Tiscornia
Presidencia Uruguay, Montevideo, Uruguay

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Ingår i: Proceedings of the 1st International Conference on Historical Cryptology HistoCrypt 2018

Linköping Electronic Conference Proceedings 149:9, s. 21-27

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Publicerad: 2018-06-13

ISBN: 978-91-7685-252-1

ISSN: 1650-3686 (tryckt), 1650-3740 (online)


We present a unique item in the history of cryptography: a woollen carpet woven in a Uruguayan penitentiary in 1980 during the dictatorship in that country. The colors of a pair of horizontally adjacent knots encrypt a single letter. The carpet is in moderately good shape, with loss of colors and some damage by moths. We had obtained the original code and here report on the deciphering. The plaintext is a political message destined to comrades outside, with a description of the political situation and directives for actions. The cryptosystem is a simple substitution. Breaking such codes is trivial. The real task here is to translate the knots into a machine-readable representation of their colors, in the presence of unclear colors and damage to parts of the carpet. The encrypted carpet is an important document from the dark times of the Uruguayan dictatorship, manufactured by prisoners from the guerrilla movement Tupamaros. Two of the present authors (JJC and JT) were active members of this group. Their personal memories were essential for our successful reconstruction of the plaintext.


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