(1) Alice wants to send Bob a physical letter.

(2) Alice also wants Bob to be confident that she sent the letter and not an imposter.

(3) Alice is confident that a potential imposter will not be able to intercept any letter she sends.

(4) Alice has previously in-person provided Bob a RSA Public key.

Can Alice use a RSA Signature to confirm she sent the letter?

What is the best approach Alice can take, that makes such verification as easy as possible for Bob?


A QR code can hold a bit over 2kiB. That's plenty for a short letter and a signature. If more is needed, use more than one QR code, and number them for ease of use.


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