What password requirement will have the highest impact in preventing brute force attacks?

Increasing the minimum password length will have the highest impact in preventing brute force attacks because longer passwords exponentially increase the possible combinations that an attacker would need to try in order to successfully guess a password. Brute force attacks rely on the attacker systematically trying every possible combination until they find the correct password.

When the minimum password length is increased, the number of potential combinations grows significantly. For example, if a password is only 6 characters long using a set of 26 lowercase letters, there are only about 308 million possible combinations. However, if the password length is increased to 12 characters, the number of combinations skyrockets to over 95 trillion if numbers and symbols are included as character sets. This huge increase in complexity makes it much more challenging and time-consuming for attackers to succeed.

While other factors, such as complexity requirements, character variety, and password history, can enhance password security, they do not contribute as significantly to mitigating brute force attacks as increasing the password length does. Complexity and variety help make passwords harder to guess by individuals or tools, but they do not change the core challenge posed by brute force attacks in the same way that increasing length does.