The BEST method to mitigate the risk of a dictionary attack on a system is to

A hardware token provides multi-factor authentication and reduces the impact of a compromised password, but it does not directly mitigate the dictionary attack against the password itself.

Complex passphrases combine length, randomness, and character variety, which exponentially increases the number of possible combinations an attacker must try, rendering dictionary-based wordlists ineffective. Unlike simple passwords, passphrases that are long and non-dictionary-based cannot be cracked by iterating through known word lists. This directly neutralizes the mechanism of a dictionary attack at its core.

Password history prevents reuse of old passwords but does nothing to stop an attacker from attempting dictionary-based guesses against a current, potentially weak password.

Encrypting the ACL protects access control entries from unauthorized viewing or tampering but has no effect on preventing brute-force or dictionary-based password guessing attempts.