A security engineer looks to change the Extensible Authentication Protocol (EAP) authentication method. If the current solution uses the Protected Access credential, which EAP implementation does the engineer look to replace?

The correct answer is found by understanding the relationship between the Protected Access Credential (PAC) and the EAP methods. The PAC is specifically associated with EAP-FAST, which utilizes a PAC to facilitate secure communications over the network. In the context of EAP implementations, EAP-FAST is particularly distinguished by its reliance on PACs for establishing protected tunnels, making it the targeted protocol when a change is sought from a solution currently using Protected Access Credentials.

Each of the other EAP methods listed operates under different mechanisms or authentication strategies. For instance, PEAP creates a secure tunnel and then uses another EAP method inside it, but it does not inherently utilize PACs. EAP-TTLS also allows for tunneling, but like PEAP, it does not rely on PACs. EAP-TLS, on the other hand, utilizes certificates for authentication rather than PACs, thereby making it unsuitable for replacement whenever the current solution is reliant on the Protected Access Credential system.

This foundational understanding of how PACs are utilized specifically within EAP-FAST highlights why the focus is correctly on this implementation for reassessment or replacement within the context given.