They decrypt Francoist telegrams encrypted with the PILAR key

They decrypt Francoist telegrams encrypted with the PILAR key

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The Cryptography Laboratory of the University of Malaga has decoded 14 telegrams sent in 1940 from the General Directorate of Security in Madrid to the Civil Government of Malaga, identifying an unknown 'cipher' called PILLAR.

Among other issues, the texts warned about a distribution of leaflets of Alianza Democrática Española, one of the first groups opposed to Francoism after the Civil War.

The vast majority of Spanish historical archives keep encrypted documents among their funds that have not been decrypted to date. This is the case of the Provincial Historical Archive of Malaga and of more than a dozen telegrams dated in the 1940s, used in communications between the General Directorate of Security, in Madrid, and the Civil Government of Malaga.

Now, a work coordinated by Dr. Alberto Peinado, deputy director of the E.T.S. of Telecommunication Engineering of the University of Malaga (UMA), has deciphered 14 of these telegrams, identifying a codification so far not registered in the catalog of systems used in Spain.

Despite the poor state of conservation with which they were incorporated into the Archive, it is clearly observed in some of them that they were encrypted using the same encryptor, identified as PILAR Key”, Explains Dr. Alberto Peinado, researcher of the Biomedical Signal Processing, Intelligent Systems and Communications Security (BIOSIP) group, and coordinator of the Cryptography Laboratory of the UMA.

This coding, of which there was no evidence in the current records of this type of systems, belongs to the so-called ‘moving tape’, a method proposed by the Government of Spain at the end of the 19th century for the entire Administration and which was in use for around 50 years.

In this technique, you assign two-digit numbers to each letter of the alphabet, two tapes were generally used, one fixed and the other mobile, on a table that contained all these numbers. The fixed belt had only the mission of serving as a reference to indicate the position in which the moving belt was placed.

Homophone assignment

For its part, moving belt, was the one that determined the assignment of these numbers (homophones) to each of the letters of the alphabet, so that once placed in their final position, the homophones applied in the encryption of a character are those listed in the column of the table in which the same letter has been placed.

The ciphertext It is distributed in fourteen documents that constitute a total of eight messages in telegram format. Specifically, they correspond to emails sent on behalf of the General Director of Security, José Finat y Escrivá de Romaní, and deal with various content, such as a notice about the possible distribution and posting on facades of flyers from the Spanish Democratic Alliance, the instructions to carry out the corresponding surveillance in the streets and post offices with the aim of arresting those responsible, or the prohibition of foreigners from bringing any type of press into Spain.

Along with the decryption of the messages, the main objective of the work has been the reconstruction of the homophone table and the fixed and moving tapes. “In this case, the team developed a method that allowed us to simultaneously reconstruct the moving tape and the homophone table, as well as a partial reconstruction of the fixed tape from various encrypted telegrams”Says Peinado.

In fact, the study of the documents has allowed the experts to generate 12 different homophone tables, together with their corresponding moving tapes; which in the future will allow the decryption of any message encoded with the PILAR key.

Document of the month in the exhibition of the Provincial Historical Archive of Malaga.

During the month of June, the Provincial Historical Archive of Malaga exposes the 14 telegrams together with the reconstruction of the encryption system. In the presentation of the ‘Document of the month’, held this morning at the exhibition site, Alberto Peinado has valued as positive the experience in terms of conservation of the historical documentary heritage, but also for obtaining the PILAR key.

"From now on, if similar telegrams are rescued, their decryption will be much easier," says the researcher, who also announces future collaboration with the Archive in cryptography work. Likewise, the Cultural delegate of the Junta de Andalucía, Monsalud Bautista has highlighted the "excellent research work" carried out by the Laboratory led by Dr. Peinado, as well as the importance of the Historical Archives as curators of the documentary heritage .

This work has been financed by the Andalucía Tech International Campus of Excellence and the Ministry of Economy, Industry and Competitiveness, the State Research Agency and the European Regional Development Fund through the COPCIS project.

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Video: Public Key Cryptography - Computerphile