Which security measure reduces the likelihood of unauthorized users gaining access?

Strong authentication is a crucial security measure that significantly reduces the likelihood of unauthorized users gaining access to systems and sensitive data. This approach requires users to provide multiple forms of verification before granting access, typically combining something they know (like a password), something they have (like a security token or smartphone), and sometimes even something they are (like biometric data).

By implementing strong authentication mechanisms, organizations create a robust barrier against unauthorized access attempts. Even if an attacker has obtained a user's password, without the additional verification methods, they would still be unable to gain access.

The other measures serve important roles in security but do not directly address user authentication in the same way. For instance, while encryption protects data confidentiality, it does not prevent unauthorized users from attempting to access a system. Firewalls are primarily focused on controlling incoming and outgoing network traffic based on predetermined security rules, which may not specifically authenticate users. Access control lists help in managing permissions but rely on the underlying authentication mechanisms to determine who can access resources in the first place.