A PDF scan of the paper is now available, so you can judge for yourself: * https://web.archive.org/web/20180928121748/https://www.gchq.gov.uk/sites/default/fil

A PDF scan of the paper is now available, so you can judge for yourself: * https://web.archive.org/web/20180928121748/https://www.gchq.gov.uk/sites/default/files/document_files/Cliff%20Cocks%20paper%2019731120.pdf https://web.archive.org/web/20180928121748/https://www.gchq.... IANAM (mathematician), but the formulae look RSA-like, though given the compute at the time, it may have been (too) expensive to try implementing.