Tom, a cybersecurity specialist at TechGuard Solutions, is responsible for enhancing the authentication and integrity of communications within the company's network. To achieve this, he adopts a security model where each user manages a set of public keys. In this setup, when a user wishes to encrypt a message, they employ the public key of the intended recipient. This ensures that only the designated recipient, armed with their private key, can decrypt the message. What is the particular security model implemented by Tom to bolster the security of corporate communications?