Brute Force Attack Strategies

TL;DR

Brute force attacks try every possible combination to guess a password or key. Attacking in order is predictable and easier to defend against (e.g., with rate limiting). Random attacks are harder to block, but take longer on average. This guide explains the differences and how they impact security.

Understanding Brute Force Attacks

A brute force attack systematically tries all possible combinations of characters until it finds the correct password or key. The effectiveness depends heavily on the length and complexity of the target, and the strategy used by the attacker.

1. Ordered (Dictionary) Attacks

This is the simplest form. Attackers use a list of common passwords, words from dictionaries, names, dates, or predictable variations. It’s fast if the password is weak.

• How it works: The attacker starts with ‘password’, then ‘123456’, then ‘qwerty’, and so on.
• Advantages for the attacker: Quick to test common passwords.
• Disadvantages for the attacker: Easily defeated by strong, unique passwords.
• Defenses:
  • Password complexity requirements (minimum length, mixed case, numbers, symbols).
  • Rate limiting – block attempts after a few failures.
  • Account lockout policies.
  • Monitoring for common password attempts in logs.

2. Random Brute Force Attacks

This method generates completely random character combinations. It’s slower but more difficult to detect and block.

• How it works: The attacker creates a string of random characters (e.g., ‘aB9z$2’).
• Advantages for the attacker: Less predictable, harder to identify patterns for blocking.
• Disadvantages for the attacker: Significantly slower than ordered attacks; requires more computing power.
• Defenses:
  • Rate limiting (more aggressive).
  • CAPTCHAs – verify human interaction.
  • Multi-factor authentication (MFA) – adds another layer of security beyond the password.
  • Web Application Firewalls (WAFs) to detect and block suspicious activity.

3. Hybrid Attacks

Attackers often combine both approaches. They might start with a dictionary attack, then switch to random combinations for passwords that aren’t found in the list.

4. Impact of Password Length and Complexity

The number of possible password combinations grows exponentially with length and complexity. A longer, more complex password takes far longer to crack, even with a random attack.

• Example: An 8-character password using lowercase letters only has 40,320,000 possibilities.
• Example: An 8-character password using lowercase and uppercase letters, numbers, and symbols has over 68 billion possibilities.

5. Tools Used in Brute Force Attacks

Attackers use various tools:

• Hydra: A parallelized login cracker that supports many protocols.

  hydra -l username -P /path/to/password_list target_ip service

• John the Ripper: A password cracking tool with various modes.
• Hashcat: A fast and advanced password recovery utility.

6. Protecting Against Brute Force Attacks

1. Strong Passwords: Enforce strong password policies (length, complexity, uniqueness).
2. Rate Limiting: Limit the number of login attempts per IP address or user account within a specific timeframe. For example, block after 5 failed attempts in 1 minute.
3. Account Lockout: Temporarily lock accounts after multiple failed login attempts.
4. Multi-Factor Authentication (MFA): Require users to provide a second form of verification (e.g., code from an authenticator app).
5. CAPTCHAs: Use CAPTCHAs to distinguish between humans and bots.
6. Web Application Firewalls (WAFs): Deploy WAFs to detect and block malicious traffic, including brute force attempts.
7. Regular Security Audits: Regularly review your security measures and logs for suspicious activity.