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1

I want to know if the following would also be equally secure Yes, both schemes are equally secure. Also for what you are trying to achieve you really shouldn't puzzle things together yourself but rather use pre-made modes like AES-GCM, AES-EAX or ChaCha20-Poly1305. In fact, we can prove the above claimed security equivalence. Because Encrypt-then-MACis ...


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We don't know. Although it seems unlikely to the extreme that there is some kind of mathematical equation that gets easier to solve when the second key relies on the first key, we probably cannot prove it. So that's it for the theoretical problems. One practical problem is that when the key for confidentiality is obtained by the adversary (e.g. through a ...


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If they have a pre-shared key $K$ and want to authenticate public keys, the simplest way would be for Alice to compute $T = HMAC(K, PubKeyAlice)$ and send $(PubKeyAlice,T)$ to Bob. This authenticates the public key of Alice. There is no need to encrypt it, since it is a public value anyway.


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Your goal, if I have understood correctly, is to create an unforgeable bearer token which you will send to a user, and which the user can later present to you in order to gain access to a resource, say a file. An adversary should be unable to guess any tokens they weren't given outright, even if they are given many many tokens. You appear to be constrained ...


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