The Biafran-war ciphers

Summary

Between 1967 and 1970, the breakaway Republic of Biafra fought a civil war against the Nigerian federal government. Biafra’s telex link to the outside world ran by radio through Lisbon. In 1969 Frode Weierud, then an engineering student and radio amateur in Oslo, intercepted and printed some of the Lisbon-to-Biafra traffic. Sweden’s signals intelligence agency (FRA) was also listening, but the ciphers had never been described in print. With George Lasry and Frode Weierud, I deciphered all the messages written in five-letter groups (24 messages in 41 parts from 1969, and three earlier ones from 1968) and read what Biafra’s overseas representatives were reporting. Four messages in five-figure groups remain unsolved.

Approach

The messages were enciphered with variants of columnar transposition. After transcribing the printouts, we found the first solutions by computer hill-climbing, reconstructed the rest of the system by hand, recovered the keywords and the indicator method (a base key plus a key for each message), and then worked out the codewords and names in the decrypts. The Cryptologia paper below gives the details.

Publications and media

Bean, R., Lasry, G. and Weierud, F. (2022). Eavesdropping on the Biafra–Lisbon link: breaking historical ciphers from the Biafran war. Cryptologia 46(1):1–66 (published online 2020). doi:10.1080/01611194.2020.1762261. Local copy: The_Biafran_Ciphers.pdf.

Bean, R., Lasry, G. and Weierud, F. (2020). We decrypted messages from the Biafran war that have remained secret for 50 years. The Conversation.

Conference talk: NSA 2022 Cryptologic History Symposium, Online

See also the full publications list and the presentations archive.