Howto建立StrongPasswords:A科學BackedGuide
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How to Create Strong Passwords — A Science-Backed Guide
1. Why password strength matters
- Password cracking rigs can test 10¹¹ to 10¹² guesses per second using GPUs.
- A 8-character password with only lowercase letters has 26⁸ ≈ 2×10¹¹ combinations — crackable in seconds.
- A 16-character passphrase with 4 random words has ~2⁴⁴ bits of entropy — computationally infeasible to brute force.
2. Length beats complexity
- NIST SP 800-63B (2017, still authoritative) recommends prioritizing length over complexity.
- Minimum 12 characters; 16+ recommended for high-value accounts.
- A 16-char lowercase password (75 bits) is stronger than an 8-char complex one (~52 bits).
3. Use passphrases, not passwords
- Diceware / EFF word-list passphrases: 4-6 random words separated by hyphens.
- Example: "correct-horse-battery-staple" — memorable and ~44 bits of entropy.
- Easier to type and remember than "Tr0ub4dour&3" while being cryptographically stronger.
4. Character diversity (when length is constrained)
- Mix uppercase, lowercase, digits, and symbols when sites cap length.
- Avoid predictable substitutions (a→@, o→0, i→1) — crackers know these.
- Place symbols/digits in the middle, not at the end.
5. Never reuse passwords
- Credential stuffing attacks use leaked password databases to breach other sites.
- Use a password manager (Bitwarden, 1Password, KeePassXC) to generate unique passwords per site.
- Check haveibeenpwned.com to see if your email appears in known breaches.
6. Enable two-factor authentication (2FA)
- TOTP apps (Aegis, Authy, Google Authenticator) are stronger than SMS codes.
- Hardware security keys (YubiKey, FIDO2) are strongest — phishing-resistant.
- 2FA turns a single-point-of-failure password into a two-factor defense.
7. Avoid these common mistakes
- Don't use personal info: names, birthdays, pet names, sports teams.
- Don't use keyboard walks: "qwerty", "asdfgh", "1qaz2wsx".
- Don't reuse the "base password + site name" pattern — it's predictable.
- Don't store passwords in plaintext files or browser autofill for high-value accounts.
8. Entropy — the math of strength
- Entropy = log₂(charsetSize^length) = length × log₂(charsetSize).
- Lowercase letters: 4.7 bits/char. Mixed case + digits + symbols: ~6.5 bits/char.
- Aim for ≥ 80 bits for general accounts, ≥ 128 bits for encryption keys.
References: NIST SP 800-63B · EFF Diceware Word List · Have I Been Pwned.
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