In public$-$key cryptography, owners keep their private$-$keys private and never exchange them. But, owners can share public keys anywhere they like. How can you be sure that the public key that one entity is using to communicate with the other entity is$,$ in fact, that entity's public key? What if the public key, in fact, belongs to a malicious third party performing a man$-$ in$-$the$-$middle attack? What is countermeasure to avoid this scenario?

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Security Certificate

Authentication token

Firewall

None of the above