Generating visible RSA public keys for PKI

In this paper, we propose the general procedures for generating a visible RSA public key for overcoming the drawback of people (without cryptographic background) not understanding what is meant by “public key”. Instead of generating a randomlike public key, a visible public key system allows the user to use a predefined image (e.g., picture, photo, signet, or handwriting signature) as his/her visible public key such that other users can decode the image as the receiver’s/signer’s public key directly for encrypting a message or verifying a signature. Of course, our procedures can also be applied to a predefined sound and/or video to generate an audible or audio-visual public key. Two algorithms for generating visible RSA public keys based on generating RSA moduli with a predetermined portion are proposed. One is suitable for the environment where all users use a common exponent, and the other is for different exponents. The constructions are almost as efficient as the generation of RSA moduli with a predetermined portion. The quality of the resulting visible public keys is almost the same as the original image, without compromising security. Experimental results show that the size and quality of visible public keys can be accepted by human eyes for practical applications.