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What do I need to look for in a crypto library to achieve this? There are multiple options for this (from most to least desirable): You want any public-key encryption scheme and any MAC algorithm and distribute as your public key, the encryption scheme's public key and the MAC key. Then you enforce that every message either has the MAC applied on the ...


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A paper was published in 2015 describing a scheme called Anonize to do just that. It appears to be constructed around a specially designed Non-Interactive Zero-Knowledge Proof of Knowledge (NIZKPoK) protocol used by clients. First, a registration is made, whereby a client sends a commitment to a seed of a pseudo-random function. Sent back to it by the ...


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A nonce on its own does not prevent replay attacks. It is just a number, it doesn't do anything, it can't give any guarantees. You could define a protocol with a nonce, that has no cryptographic functions at all - and it's fairly obvious, that is not secure in any sense. It all comes down to how you use the nonce in a protocol and what kind of security ...


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Given no knowledge of the MAC key and that M1 != M2, it is not possible to compute MAC(K, M2) from MAC(K, M1). More generally, it isn't possible to determine the MAC of any message you haven't already seen. (Again, without the key.) The definition of a nonce is a number which is only used once with a given key. Bob ensures that nonces are only used once ...


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The aspects regarding IV has already addressed @Maarten - reinstate Monica. There are some more issues. 1) If you store encrypted data in cookies once for all future requests, then it will not work, because many users clean cookies and local storage regularly. Some do that manually, some use add-ons that clean up cookies and local storage on browser exit or ...


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