How Password Generators Work & Why You Need One in 2025

What Makes a Password "Strong"?

A strong password is one that cannot be guessed or cracked within a reasonable timeframe using automated attacks. Password strength is primarily a function of two factors: length and character set size. Together, these determine the number of possible combinations an attacker must try.

The formula is simple: possible combinations = character_set_size ^ password_length. For example:

• A 6-character lowercase password: 26^6 = 308,915,776 combinations — crackable in under a second
• A 12-character mixed-case + numbers + symbols password: 94^12 = 475,920,314,814,253,376,475,136 combinations — takes centuries to crack by brute force

The NIST Special Publication 800-63B (2024 updated guidelines) recommends passwords of at least 8 characters, but security experts widely recommend 16+ characters for accounts that cannot use multi-factor authentication.

What Is a Cryptographically Secure Password Generator?

Not all random number generators are equal. JavaScript's Math.random(), for example, produces numbers that appear random but are generated by a deterministic algorithm (a pseudorandom number generator, or PRNG). Given enough outputs, a determined attacker can predict future values — making passwords generated this way theoretically predictable.

A Cryptographically Secure Pseudorandom Number Generator (CSPRNG) uses entropy from your device's hardware (keyboard timing, mouse movements, hardware noise) to generate numbers that are truly unpredictable even if the attacker knows the algorithm. Browsers expose this via window.crypto.getRandomValues().

DocsConverter's Password Generator uses crypto.getRandomValues() exclusively. This is the same API used by banking applications and VPN software for key generation — and it runs entirely in your browser.

How Password Generation Works Step by Step

1. Build the character pool — Based on your settings (uppercase, lowercase, numbers, symbols), a string of valid characters is assembled. For example: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!@#$%^&*()"
2. Request random bytes — crypto.getRandomValues() fills a typed array with cryptographically random bytes from the OS entropy pool.
3. Map bytes to characters — Each random byte is mapped to an index in the character pool using modulo arithmetic. To avoid modulo bias (which would make some characters slightly more likely), the implementation discards values that would create bias.
4. Assemble the password — The selected characters are joined into the final password string.
5. Validate requirements — If you've specified that the password must contain at least one symbol, the generator verifies this is the case and regenerates if not.

Password Entropy: The True Measure of Strength

Security professionals measure password strength in bits of entropy. Entropy = log2(character_set_size^length) = length × log2(character_set_size).

Password Type	Length	Entropy	Time to Crack (offline)
Lowercase only	8	37.6 bits	Seconds
Mixed case + numbers	12	71.5 bits	Days–weeks
All characters (94)	16	105 bits	Centuries
All characters (94)	24	157 bits	Heat death of universe

Security experts generally recommend targeting at least 80 bits of entropy for standard accounts and 128+ bits for high-value accounts (banking, email, primary password manager).

NIST 2024 Password Guidelines: What Changed?

NIST's 2024 update to SP 800-63B made several important changes from the previous version that are now considered best practice:

• No more mandatory periodic password rotation — Forced password changes every 90 days were found to actually decrease security (users make predictable, minimal changes like "Password1!" → "Password2!"). Change passwords only when there's evidence of compromise.
• No more complexity rules — Requiring uppercase, lowercase, numbers, AND symbols was found to create predictable patterns (P@ssw0rd). Instead, focus on length.
• Allow all printable ASCII characters — Including spaces. Passphrases (long phrases) are encouraged.
• Check passwords against breach databases — Passwords should be checked against known-compromised password lists and rejected if found.
• Minimum 8 characters, recommended 15+ — Longer is always better.

Password Manager Integration: The Complete System

A password generator is only useful as part of a complete password management system. The workflow is:

1. Use a password manager (Bitwarden, 1Password, Dashlane) as your primary vault
2. For every new account, generate a unique, strong password using either the manager's built-in generator or DocsConverter's tool
3. Never reuse passwords between accounts — a single breached site should not compromise all your accounts
4. Enable multi-factor authentication (MFA) on every account that supports it
5. Use a unique, very strong master password for your password manager — this is the one password you need to remember

Common Password Mistakes

• Reusing passwords — The most dangerous mistake. When one site is breached, all accounts with that password are compromised.
• Password patterns — Replacing letters with numbers/symbols predictably ("@" for "a", "0" for "o", "!" at the end). Crackers use these rules.
• Dictionary words — Even with character substitutions, dictionary-based passwords are weak against rule-based cracking.
• Personal information — Birthdays, names, pet names, and addresses are guessable by anyone who knows you and are tried first in targeted attacks.
• Short passwords — Any password under 12 characters with a limited character set is vulnerable to modern GPU-accelerated brute-force attacks.

Frequently Asked Questions

Is it safe to generate passwords in a browser?
Yes, if the tool uses crypto.getRandomValues() and processes everything locally. DocsConverter's generator never sends your password to any server — it's generated and displayed entirely in your browser.

Should I use passphrases instead of random passwords?
Passphrases (e.g., "correct-horse-battery-staple") are excellent if you need to memorize a password. For passwords stored in a manager, random character passwords provide more entropy per character.

How long should my password be?
A minimum of 16 characters for standard accounts, 24+ for high-value accounts. With a password manager, there's no reason not to use 32-character passwords everywhere.

What if I need to type my password on a device?
If you frequently need to type a password (e.g., on a TV, game console, or shared computer), consider a passphrase — long but composed of memorable words — rather than a random character string.