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The scenario: Alice wants to exchange information with Bob on an encrypted channel proxying through Pete (Pete can't read the info sent between Alice and Bob), but doesn't want Bob to know who she is, she could use unilateral authentication with a KEM. Bob creates and signs an ephemeral public key, and sends it to Alice via Pete. Alice creates a symmetric key with a RNG, and encrypts it with Bob's ephemeral public key, without signing anything.

The question: When Bob receives and decrypts the symmetric key, should he then send a signed hash of it to Alice via Pete to make sure that Alice knows that the key has been unchanged when it arrived to Bob, ie should it be a hash like Sha2/Sha3, or something like Argon2/Scrypt, or something different all together?

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  • $\begingroup$ Did you Libsodium Sealed box? $\endgroup$ – kelalaka Dec 23 '19 at 13:42

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