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?
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The answer here might be of some interest. – Modal Nest Dec 17 '20 at 16:24
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Also this – kelalaka Dec 17 '20 at 16:26
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1Are 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. – Maarten Bodewes Dec 17 '20 at 18:32