Password Strength Analysis Guide: Evaluate and Generate Secure Passwords
Three Dimensions of Password Strength
A password's security is determined by three core dimensions:
1. Length
Length is the most important factor. Each additional character multiplies brute-force attempts by the charset size.
| Length | Digits-Only Combinations | Crack Time (1B/sec) |
|---|---|---|
| 4 | 10,000 | Instant |
| 6 | 1,000,000 | 0.001 sec |
| 8 | 100,000,000 | 0.1 sec |
| 12 | 1 trillion | 17 min |
| 16 | 10 quadrillion | 50 years |
| 20 | 100 quintillion | 30,000 years |
2. Charset Size
A larger charset means more combinations per character:
| Charset | Available Characters | Example |
|---|---|---|
| Digits only | 10 | 0-9 |
| Lowercase | 26 | a-z |
| Upper + lower | 52 | a-z, A-Z |
| Upper + lower + digits | 62 | a-z, A-Z, 0-9 |
| Full charset | 95 | a-z, A-Z, 0-9, !@#$%... |
3. Entropy
Entropy measures password randomness mathematically:
Entropy (bits) = log₂(charset_size ^ length) = length × log₂(charset_size)
| Password | Charset | Length | Entropy | Rating |
|---|---|---|---|---|
123456 |
Digits | 6 | 19.9 bit | Very weak |
abc123 |
Lower+digits | 6 | 31.0 bit | Weak |
Abc123 |
Mixed+digits | 6 | 35.7 bit | Weak |
Kx9#mP2v |
Full | 8 | 52.6 bit | Medium |
Kx9#mP2vLq5! |
Full | 12 | 78.9 bit | Strong |
Kx9#mP2vLq5!nR8@ |
Full | 16 | 105.2 bit | Very strong |
Industry standard: entropy ≥ 80 bit is strong, ≥ 100 bit is very strong.
Common Attack Methods
Brute Force
Try every possible combination. Defense:
- Increase length and charset
- Use account lockout and rate limiting
Dictionary Attack
Try common passwords from dictionaries (e.g., rockyou.txt with 14M entries). Defense:
- Avoid common passwords (
123456,password,qwerty) - Avoid dictionary words (
sunshine,iloveyou)
Rainbow Table Attack
Pre-compute hash tables to reverse-lookup passwords. Defense:
- Server-side salted hashing (Salt + Hash)
- Use slow hash algorithms like Bcrypt
Credential Stuffing
Use leaked credentials from one site to try logging into others. Defense:
- Unique password per site
- Use a password manager
Using the Password Strength Tool
Step 1: Open the Tool
Open Password Strength, type the password to test.
Step 2: Review Results
The tool shows in real time:
- Strength rating: Very weak / Weak / Medium / Strong / Very strong
- Entropy: In bits
- Charset analysis: Which character types are used
- Estimated crack time: Based on different attack speeds
- Improvement suggestions: How to strengthen the password
Step 3: Improve
If the rating is too low:
- Increase length (most effective)
- Add missing character types
- Avoid sequential and repeating patterns
Using the Password Generator
Creating strong passwords manually is hard. Use Password Generator instead:
Step 1: Configure
- Length: 16-24 characters recommended
- Charset: Enable upper, lower, digits, symbols
- Exclude ambiguous chars: Like
0/O,1/l/I
Step 2: Generate
Click "Generate" — produce multiple passwords to choose from.
Step 3: Verify
Paste the generated password into Password Strength to confirm it reaches "Strong" or "Very strong" level.
Password Security Best Practices
1. Use a Password Manager
- Generate unique random passwords for each site
- Remember only one master password
- Recommended: Bitwarden, 1Password, KeePass
2. Enable Two-Factor Authentication (2FA)
Even if the password is leaked, 2FA blocks unauthorized access. Prefer TOTP over SMS verification.
3. Check for Breaches Regularly
Use services like Have I Been Pwned to check if your email appears in data breaches.
4. Server-Side: Use Bcrypt
If you're a developer, always hash passwords with Bcrypt (salted) before storage. Never store plaintext passwords.
Common Misconceptions
"Complex rules = strong password"
Many sites require upper+lower+digit+symbol, but P@ssw0rd meets all rules yet is trivially cracked by dictionary attacks. Length matters more than complexity rules.
"Replacing letters with symbols is secure"
p@$$w0rd substitution patterns are already covered by attack tools. Don't rely on simple character substitution.
"Never changing my password is fine"
If your password has been leaked, not changing it means you stay exposed. Check for breaches regularly and change immediately if compromised.
"Strength checkers leak my password"
ToolsKu's Password Strength runs entirely in your browser. Your password is never sent to any server.
Related Tools
- Password Strength — Evaluate password security
- Password Generator — Generate random strong passwords
- Bcrypt Hash — Salted hashing for password storage
Summary
The core of password security is sufficient entropy, determined by length and charset size. Use Password Strength to evaluate existing passwords, Password Generator to create strong ones, and combine with a password manager and 2FA for complete account security. Remember: length first, unique per site, local processing, server-side salting.