Securing and authenticating messages is easy thanks to computers. Lately I've been thinking about something like Vigenère cipher with a OTP, how secure it is, and how easy it is to implement without the aid of computers. However, one thing it doesn't provide is any authentication. Decrypting a Vigenère cipher with pen and paper is trivial, but hand calculating HMAC-SHA256 is not something I'd like to attempt. Are there any authentication schemes which are simple; easy to compute without the aid of a computer? Any chance any of those schemes actually provide decent security?

  • $\begingroup$ The answer here might be of some interest. $\endgroup$
    – Modal Nest
    Dec 17, 2020 at 16:24
  • $\begingroup$ Also this $\endgroup$
    – kelalaka
    Dec 17, 2020 at 16:26
  • 1
    $\begingroup$ Are there any parts in your question that are not answered in the first link provided, Chris_F? If so, please try and focus your answer on those parts. As it stands it very much looks like a dupe to me. $\endgroup$
    – Maarten Bodewes
    Dec 17, 2020 at 18:32


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