Password Managers: How They Work and Are They Safe?

What is a password manager?

A password manager is a program that generates, stores and fills in your passwords ^[2]. It may be built into your web browser or phone, or it can be a separate app from a third party ^[1]. You unlock it with one primary password (often called the master password), so you only need to remember one strong password ^[2].

The main benefit is that you can use a unique password for every service, because you no longer have to remember them ^[1]. That matters because reused passwords spread damage. The NCSC explains that if one account is compromised, a hacker can try the same password on your other accounts ^[1].

Most managers also offer ^[1]:

• Password generation: creating a strong, unique password for each account.
• Autofill: entering the password for you, which also helps against phishing because it fills only on the correct website.
• Syncing: making your passwords available on all your devices.
• Breach warnings: alerting you when a saved password has been leaked.

Do security agencies recommend them?

Yes. CISA, the US cybersecurity agency, advises using a password manager to store all passwords and protecting the vault with a strong passphrase ^[3]. NIST's 2025 guidelines go further for websites: services must allow password managers and autofill, and should allow pasting passwords ^[4].

How does a password manager keep passwords secure?

Your saved passwords sit in an encrypted file called a vault. Bitwarden's published security white paper is one detailed example of how a cloud-based manager protects it ^[5]:

1. Your master password is stretched with a key-derivation function, PBKDF2-SHA256 with 600,000 iterations by default, to create an encryption key. Users can switch to Argon2id instead ^[5].
2. The vault is encrypted on your device with AES-256 before anything is uploaded ^[5].
3. The master password and the encryption keys derived from it are never sent to or stored on Bitwarden's servers; the server receives only a hash of the master password, used to check logins ^[5].
4. The servers store and sync the vault data only in encrypted form, and Bitwarden says its staff cannot see your passwords ^[5].

This design is often marketed as zero-knowledge encryption: the company should not be able to read your vault even if its servers are breached. Researchers note that vendors' claims imply protection even against a fully malicious server ^[6]. Key stretching makes each guess at the master password slow, which is why a long master password matters if an encrypted vault is ever stolen; researchers have pointed to weak master passwords and low iteration counts on older LastPass accounts ^[9].

What about browser and phone password managers?

The NCSC says it is safe to let your browser or operating system save passwords on your own devices, and that Chrome, Edge and Safari all offer this ^[1]. Apple's Passwords app, introduced with iOS 18, stores passwords, passkeys, Wi-Fi passwords and verification codes. It also warns about passwords that are easy to guess, reused, or found in known data leaks ^[10]. The NCSC notes that browser-stored passwords are only as secure as your devices and accounts, so keep automatic security updates on ^[1].

Are password managers safe?

Password managers concentrate your secrets in one place, so their security has been tested in public, both by attackers and researchers. Two cases are worth knowing.

What happened in the LastPass breach?

In August 2022, attackers broke into LastPass in two linked incidents. In the second, they exploited a flaw in media-server software on a senior engineer's personal computer and installed a keylogger to steal his master password ^[8]. That gave them the keys needed to download LastPass's backup database ^[8]. In December 2025 the UK Information Commissioner's Office (ICO) fined LastPass £1.2 million. It found the company had failed to implement sufficiently robust security measures ^[8]. Up to 1.6 million UK users were affected. Names, email addresses, phone numbers and stored website URLs were taken ^[8].

The ICO found no evidence that customers' passwords were decrypted ^[8]. Separately, in 2023, security researchers linked more than 150 victims and over $35 million in cryptocurrency thefts to seed phrases stored in LastPass. They suspected that weak master passwords on stolen vaults were being cracked offline ^[9]. The researchers said they probably could not conclusively tie the thefts to the breach, so this remains a suspicion, not a confirmed finding ^[9].

What did the 2026 ETH Zurich study find?

Researchers from ETH Zurich and Università della Svizzera italiana (USI) tested whether four cloud managers' "zero-knowledge" claims hold if the company's server is fully malicious, for example after a breach ^[6]. They presented 12 distinct attacks against Bitwarden, 7 against LastPass, 6 against Dashlane and 6 against 1Password ^[6]. Most allow passwords to be recovered, and the worst range up to full compromise of all vaults in an organisation ^[6].

The context matters. The attacks assume the attacker already controls the vendor's servers ^[7]. Many then need ordinary user actions such as logging in or syncing; others need actions like sharing or key rotation ^[7]. The researchers disclosed the findings to the vendors, and remediation is under way ^[6]. Dashlane said it removed the legacy cryptography behind its most serious issue, and LastPass disputed parts of the severity assessment ^[7]. The researchers said they could not rule out that advanced attackers already know these weaknesses ^[7].

So should you still use one?

The official advice remains yes. The NCSC ^[1] and CISA ^[3] both recommend password managers, because the alternative for most people is reusing weak passwords. The lessons from these cases are to choose a strong master password, turn on two-step verification, and keep the software updated ^[1][3].

How do password managers compare with other ways of storing passwords?

Each approach trades convenience against different risks. The NCSC accepts writing passwords in a notebook for some people, for example those who need help from family to manage accounts, because an attacker would need physical access ^[1]. It warns, though, that some banks forbid writing passwords down, that anyone with access can copy them, and that you lose autofill's protection against phishing sites ^[1]. CISA advises against saving passwords in a file on your computer ^[2].

How do you choose and set up a password manager?

The NCSC says the best password manager is the one that meets your needs and that you find easiest to use ^[1]. Things to weigh include whether it works across all your devices and operating systems, whether you can control the passwords it generates, whether you will pay or use a free version, and extras such as password sharing or breach alerts ^[1]. A third-party manager's main advantage over a browser's is syncing across a mix of browsers and devices ^[1].

1. Create a strong master password. CISA recommends passwords of at least 16 characters, either random or a passphrase of 4 to 7 unrelated words ^[2], and says the vault password should be long, unique and random ^[3].
2. Turn on two-step verification for the manager. The NCSC says this keeps criminals out even if they learn your primary password ^[1].
3. Set up recovery. If you forget the primary password, many managers offer password hints or emergency access through trusted contacts ^[1]. Set these up before you need them.
4. Replace weak passwords. Review existing passwords and change any that are not long, unique and random to ones generated by the manager ^[3].
5. Avoid shared computers. Never save passwords in the browser of a shared or public computer ^[1].
6. Add passkeys where offered. The NCSC now recommends passkeys as the first choice of login, with strong passwords and two-step verification where passkeys are not available ^[11]. Many managers store passkeys too; the NCSC calls these tools credential managers ^[12].

What password rules do official guidelines now recommend?

NIST's SP 800-63B-4, finalised in 2025, changed long-standing password rules for websites and services in ways that suit password managers ^[4]:

• Passwords used as the only factor must be at least 15 characters; passwords used with another factor must be at least 8 ^[4].
• Services should allow passwords of at least 64 characters ^[4].
• Services must not impose composition rules, such as requiring a mix of character types ^[4].
• Services must not force periodic password changes, but must force a change if there is evidence of compromise ^[4].
• New passwords must be checked against a blocklist of common, expected or compromised passwords ^[4].
• Services must allow password managers and autofill, and should allow pasting ^[4].

These rules apply to services, not to you directly. They make it easier for a manager to generate and fill long random passwords.

What is next for password managers?

Password managers are turning into general credential managers. Apple's Passwords app already holds passkeys and verification codes alongside passwords ^[10]. The NCSC expects people to keep using passwords where passkeys are not yet offered, managed by a password manager, while passkeys spread ^[11][12].

The 2026 research also put pressure on vendors' security claims. The researchers recommend onboarding new users with the latest cryptography by default and letting existing customers choose whether to migrate ^[7]. The full version of the paper, last revised in August 2026, includes additional results on 1Password ^[6].

This is general security information, not a product recommendation. Check a manager's published security documentation and update history before trusting it with your accounts.