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a simple authentication protocol would be to send a long random string challenge, and get the client to sign it Well, yes. This is the most common way to do authentication challenges. However, the protocol you describe has a major flaw: all it guarantees is that the client has seen and accepted the random challenge. This guarantees that the client was alive ...


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In many secure protocols (e.g. modern versions of SSH, TLS, etc), the two sides first proceed with ephemeral key exchange to come to a shared secret in order to setup a secure connection, then authentication takes place. Because the two sides already have a shared secret when it's time for the client to authenticate, the client can use its long-term private ...


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What issues is there with this approach? There are both theoretical and practical concerns with this kind of solution. First, it is generally not seen as a good idea these days to just sign whatever the somebody else handed you, especially if you also use the signing key in other contexts. This is to prevent an attacker from sending you a "challenge&...


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Let's break apart the property description: An active attacker So an attacker who can both read and create packets on the network who pretends to be the initiator In the NK1 handshake, the initiator is anonymous, so it's not really pretending to be the initiator, it is an anonymous initiator like any other NK1 initiator and records a single protocol run ...


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As I understand, GCM will also be broken by quantum computing The idea that GCM would be broken is, at best, questionable; it is broken only in the scenario where you allow the attacker to make entangled queries, and is returned entangled answers. That is, for this to be an applicable attack, the implementation under attack must also be a Quantum ...


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You are describing linkable ring signatures. Here's a paper from ICCSA that goes into the model and proposes some schemes.


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