Strong Password Requirements: A secure password should contain a mix of uppercase and lowercase letters, numbers, and special symbols. This significantly increases the time needed for attackers to crack it using brute-force methods.

Password Length: Length is the most important factor in password security. A 12-character password is considered the minimum, but 16+ characters are recommended for critical accounts like banking or email. The computational effort increases exponentially with each additional character.

Entropy Calculation: Password strength is measured in bits of entropy. For a password using all 4 character types (94 possible characters), the formula is: $Entropy = \log_2(94^{length})$. For example, a 12-character password with all types has ~79 bits of entropy.