How to Create Strong Passwords That Actually Protect You

How attackers actually guess passwords

Very few accounts are broken by someone typing guesses into a login page, because most services limit repeated attempts. The real danger is offline guessing. When a company suffers a data breach, attackers often obtain its database of stored password hashes. They can then test billions of guesses per second on their own hardware, with no lockout and no one watching.

Attackers do not start with random strings. They start with lists of passwords leaked in earlier breaches, common words, names, keyboard patterns like qwerty123, and predictable substitutions such as replacing a with @ or o with 0. They append years and exclamation points because people do. Any password a human invents by following a pattern is far weaker than its length suggests.

The other major threat is credential stuffing. If you reuse a password and one site leaks it, attackers will automatically try the same email and password on banks, shops and email providers. A perfect password used in ten places is only as safe as the weakest of those ten sites.

Entropy: measuring unpredictability

Security professionals describe password strength in bits of entropy. For a password generated truly at random, entropy equals the length multiplied by the base-2 logarithm of the number of possible characters. Each additional bit doubles the number of possibilities an attacker must search.

The character set matters, but less than people think. Lowercase letters alone give 26 options, about 4.7 bits per character. Adding uppercase and digits gives 62 options, about 5.95 bits per character. All 94 printable keyboard characters give about 6.55 bits per character. Going from lowercase only to every symbol on the keyboard adds less than two bits per character, while each extra character of length adds the full amount again.

Here is a worked example. An 8 character random password drawn from all 94 printable characters has 94 to the power of 8 possibilities, which is about 6.1 quadrillion, or roughly 52.4 bits. If a stolen hash can be tested at 10 billion guesses per second, which is realistic for a fast, poorly chosen hashing method on modern graphics hardware, trying every combination takes about 610,000 seconds, a little over 7 days. Now make it 16 random characters from the same set. That is about 104.9 bits, and at the same speed exhausting every combination would take on the order of 100 trillion years. Doubling the length did not double the work. It squared it.

One important caveat: entropy only applies to randomly generated passwords. A 16 character password made from your pet's name and birthday has nowhere near 104 bits, because an attacker's guessing list will reach it long before random searching would.

Length versus complexity, and the case for passphrases

Because length grows strength so quickly, modern guidance favors long passwords over complicated short ones. NIST's digital identity guidelines in SP 800-63B discourage forcing users to mix character types and discourage routine scheduled password changes, recommending instead that services allow long passwords, check new ones against lists of known breached passwords, and require a change only when there is evidence of compromise.

A passphrase is a sequence of randomly chosen words, such as four to six words picked from a large list. The classic method uses dice and a list of 7,776 words, one for every combination of five six-sided dice rolls. Each word adds about 12.9 bits. Six random words give 7,776 to the power of 6 possibilities, about 77.5 bits. At 10 billion guesses per second, exhausting that space would take roughly 700,000 years, and the phrase is far easier to type and remember than 12 random symbols.

The key word is random. A memorable line from a song or a sentence you made up is not random, and attackers include famous phrases and common word combinations in their guessing lists. Let dice or a cryptographically secure generator choose the words for you.

Password managers: the step that matters most

No one can memorize a unique 16 character random password for each of a hundred accounts. That is exactly why password reuse is so common, and why a password manager is the most effective improvement most people can make. A password manager stores your credentials in an encrypted vault, fills them in for you, and generates a new random password for every site.

With a manager, you need to memorize only one thing: a strong master passphrase, ideally five or six random words. Protect the vault itself with two-factor authentication. Most managers also warn you about reused or breached passwords, which turns an overwhelming cleanup job into a short list.

A few passwords should still live in your head as well as in the vault: the master passphrase, and possibly the password for your primary email account, since email is usually how every other account gets reset. Write recovery codes down and keep them somewhere physically safe.

Two-factor authentication

Two-factor authentication, often shortened to 2FA, requires something beyond your password before a login succeeds. That second factor might be a six-digit code from an authenticator app, a push approval on your phone, a hardware security key, or a passkey stored on your device.

Not all second factors are equal. Codes sent by text message are better than nothing but can be intercepted through SIM swapping, where an attacker convinces a carrier to move your number to their phone. Authenticator apps that generate time-based codes are stronger. Hardware security keys and passkeys are strongest against phishing, because they verify the real website's address cryptographically and will not respond to a lookalike site.

Turn on two-factor authentication first for email, banking, your password manager and any account that can reset other accounts.

What happens to your password: hashing basics

A well-built service never stores your actual password. It stores a hash, the output of a one-way function that turns any input into a fixed-length fingerprint. When you log in, the service hashes what you typed and compares the two fingerprints. Changing even a single character produces a completely different hash, and there is no practical way to run the function backward.

General-purpose hashes such as SHA-256 are designed to be fast, which is great for verifying file downloads but bad for passwords, because speed helps attackers guess. MD5 and SHA-1 are additionally considered broken for security purposes because collisions can be produced. Proper password storage uses deliberately slow, salted algorithms such as Argon2, bcrypt, scrypt or PBKDF2. A salt is a random value stored alongside each hash so that two users with the same password get different hashes and precomputed lookup tables become useless. You cannot control how a website stores your password, which is one more reason never to reuse one.

Using ToolWorld security tools

The ToolWorld Password Generator creates passwords in your browser using a cryptographically strong random source. You can set the length from 4 to 64 characters, choose uppercase, lowercase, numbers and symbols, switch on a pronounceable mode, and generate up to 20 at once. A strength meter rates each password, and when several are shown it displays the weakest in the list so it never overstates. A length of 16 or more with all character sets enabled is a strong default for anything stored in a password manager.

The Hash Generator computes MD5, SHA-1, SHA-256 and SHA-512 digests of text or files using the browser's WebCrypto API. It is ideal for checking that a downloaded file matches a published checksum and for seeing firsthand how a tiny change transforms a hash. It is not a substitute for a dedicated password hashing algorithm.

Developers who need machine credentials can use the API Key Generator, which produces cryptographically random keys with optional prefixes in Base64url, hexadecimal or Base62 encoding, in bulk, along with SHA-256 fingerprints. Storing only that fingerprint on the server, rather than the key itself, follows the same principle as password hashing. Pair these tools with a password manager and two-factor authentication, and you will have closed the gaps attackers rely on most.