Built-in self-authentication

Briefly describe the built-in self-authentication (BISA) technique. Consider the following scenario: A rogue foundry wants to insert Trojan in BISA-protected design. The foundry wants to replace higher driving strength gates with the same functionality lower driving strength gates, for example, replace 8x buffer with 1x buffer, to make room for Trojan cell insertion. Give your opinion if such attacks can be initiated.