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In real communications, you often don't reliably know each others' public keys. X.509 certificates provide a way to verify a public key (as the certificate is signed by another key, and that key can be in a certificate signed by a third key, and so on, until we reach a public key that the other person does trust). Certificates are unnecessary when both ...


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For public key encryption, there's an easy solution using a variant of Elgamal. (If you want to do authentication, you can use standard algorithms. If you specifically want signature schemes, say so.) Recall that the security of Elgamal is equivalent to DDH, which is talking about indistinguishability of certain subgroups, namely given a cyclic group $G$, a ...


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Yes, it is possible. Steve Gibson's SQRL does a similar thing: the user has a master private key, which is hashed together with a domain name to produce a site-specific public/private key pair. (The hash in this case is HMAC-SHA256, with the domain name used as the message.) Your post doesn't mention what kind of services this will be for. If SSH, then you ...


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Is this possible? Yes. Is there any existing solution which satisfies the above requirements? That depends on what you mean by "existing". Trapdoored key generation can be used for that. x is the chosen key generation algorithm, K$_{\text{priv}}$ and K'$_{\text{priv}}$ are both its trapdoor, and the derivation of K'$_{\text{pub}}$ simply ignores ...



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