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Zero-Knowledge password managers

How a password manager encrypts your vault from the master password, and what you do so that it really protects your accounts.

In 30 seconds

Where it happens
Every time a password is created, typed or saved, at work as at home.
What the attacker wants
The master password or the plaintext credentials extracted from memory10, because a successful attack gives access to all the stored passwords1.
The reflex
Choose a long, unique passphrase as the master password56, turn on multifactor authentication on the manager1 and never reuse that secret elsewhere4.
If it's already done
Find out whether a recovery option exists, who can trigger it, and whether you want it1.

What it is

A password manager keeps an employee's credentials in a vault. The vault opens with a single secret, the master password1. The dozens of passwords each person uses are hard to remember, and people reuse the same ones or choose common passwords, which attackers exploit1.

In the ideal case described by the NCSC, the key that decrypts the vault is generally derived from the master password, and it should not be accessible to the provider of the synchronisation service1. This property has a downside: if the decryption key is lost, it must not be possible to reset it in order to recover the contents of the vault1.

Straight answers

Can the provider read my passwords?

The NCSC (UK) guide describes the ideal case: the stored credentials are accessible only to the user, with their decryption key, generally derived from the master password. This key must not be accessible to others, the provider included1. A manager that offers recovery by the provider departs from this case: the NCSC warns that the recovery method can be exploited to gain access to the credentials, especially when the provider is responsible for it1.

What happens if I forget the master password?

You lose access to all your saved passwords and must reset the affected accounts one by one, which takes a lot of time1. Some managers offer a recovery that involves other authorised people: a colleague, an administrator or the provider1. The NCSC recommends deciding whether you want this option by weighing its risks against the cost of a lost vault1.

Why isn't the master password used as is as the key?

A key derivation function turns the password into an encryption key. In December 2010 NIST published recommendation SP 800-132, which describes the derivation of master keys from passwords or passphrases to protect stored data2. NIST states in 2023 that it plans to revise this document2.

Can a password manager be attacked?

Yes. The NCSC points out that, like any software, a manager can have vulnerabilities, and that it is a natural target since a successful attack gives access to all of a user's passwords1. The same guide concludes that the benefits outweigh the risks1.

1How it works1 min

The master password goes through a derivation function to produce the encryption key2. For storing passwords on the server side, OWASP recommends slow algorithms such as Argon2id, bcrypt or PBKDF2, and judges fast algorithms such as SHA-256 unsuitable, because they let the attacker test a very large number of combinations per second3. A slow algorithm that uses a lot of memory makes brute force harder, more costly and longer3.

The tuning is done through a work factor, that is, the number of iterations of the algorithm for each password3. OWASP gives several equivalent minimum configurations for Argon2id, one of which is 19 MiB of memory, 2 iterations and a parallelism degree of 1, and, for PBKDF2 with a FIPS-140 requirement, a factor of 600,000 or more with HMAC-SHA-2563. These figures describe server-side password storage. The sources in the file do not say which parameters each manager uses for its vault.

On the usage side, the manager also fills in forms. It must offer the credentials only for the site where they were saved, never the whole vault to a visited site1. The NCSC adds that a manager can spot fake sites better than a human can1.

2What you do2 min

Choose a long passphrase as your master password. CISA suggests a string of 4 to 7 unrelated words5. The NCSC advises three random words, for example "applenemobiro", and advises against birth dates, sports teams, and the names of relatives or pets, which social media often reveals6. Replacing an "o" with a zero adds little strength, because cybercriminals know the trick6. The CNIL gives as an example a password of at least 12 characters of 4 types, and notes that it can be shorter if the account has additional safeguards4.

Never reuse this master password. The CNIL asks for a password specific and unique to each sensitive account, in order to avoid cascading compromises4.

Turn on multifactor authentication on the manager. With it, the attacker must know the master password and hold the second factor1. The NCSC asks for it to be used on all managers with cloud synchronisation, and for privileged accounts such as administrator accounts1. OWASP cites a Microsoft analysis according to which multifactor authentication would have stopped 99.9% of account compromises7.

Decide whether you want a recovery method, by weighing its risks against the cost of a lost vault, and know who could trigger it1. If your company has a policy, follow it. The NCSC recommends that the organisation (system owners) define a clear policy on exporting the vault in plaintext, because once exported, the passwords are no longer protected1.

Let the manager generate the passwords for your other accounts: it makes it easier to use unique, long and random passwords1. NIST notes that pasting into input fields makes managers easier to use8. This version of NIST SP 800-63 has been replaced by SP 800-63-4 since 1 August 20258.

3Pitfalls1 min
  • A weak master password. The attacker can try to guess it by brute force10. For the master password policy, MITRE refers to NIST recommendations10.
  • Phishing. MITRE advises training users to recognise phishing attempts that steal session cookies or credentials10.
  • The vault open in memory. Once the database is unlocked, the credentials can be copied in memory, and attackers extract the master password or the plaintext credentials from it10. MITRE advises locking the manager again after a short delay10.
  • Outdated software. MITRE recommends regularly updating browsers, managers and related software10, and the NCSC recommends checking that the vendor fixes its flaws quickly1.
  • Extensions and the browser. The manager often relies on a browser extension to fill in forms1. MITRE lists the data of browser extensions and managers among the targets of some malware10. On a shared computer, Cybermalveillance.gouv.fr advises against saving passwords in the browser9.
  • Stolen vault databases. MITRE cites actors and malware that have targeted these databases: Threat Group-3390 obtained a KeePass database on a compromised machine, and Indrik Spider exported passwords from managers10.
  • Losing the secret without recovery. If the key is lost and no recovery exists, the vault stays unreadable1.
  • Plaintext notes. Sticky notes, text files, messaging or phones are not designed to store passwords4.

Fact sheet

Identifier
CP-201
Wing
3. Protocols and defence
Brain skill
Controlling Access (control_access)
Brain reflex
cr-013
Diagram
G3 · System & Protocol Anatomy
Languages
en, fr
Sources
10 sources checked on 3 November 2026
Sources10 sources
  1. NCSC (UK), “Password manager buyers guide”. https://www.ncsc.gov.uk/collection/passwords/password-manager-buyers-guide (accessed 3 November 2026)
  2. NIST, “SP 800-132, Recommendation for Password-Based Key Derivation: Part 1: Storage Applications | CSRC”. https://csrc.nist.gov/pubs/sp/800/132/final (accessed 3 November 2026)
  3. OWASP, “Password Storage - OWASP Cheat Sheet Series”. https://cheatsheetseries.owasp.org/cheatsheets/Password_Storage_Cheat_Sheet.html (accessed 3 November 2026)
  4. CNIL, “Les conseils de la CNIL pour un bon mot de passe”, 26 January 2017. https://www.cnil.fr/fr/les-conseils-de-la-cnil-pour-un-bon-mot-de-passe (accessed 3 November 2026)
  5. CISA, “Use Strong Passwords | CISA”. https://www.cisa.gov/secure-our-world/use-strong-passwords (accessed 3 November 2026)
  6. NCSC (UK), “Three random words”, 21 December 2021. https://www.ncsc.gov.uk/collection/top-tips-for-staying-secure-online/three-random-words (accessed 3 November 2026)
  7. OWASP, “Authentication - OWASP Cheat Sheet Series”. https://cheatsheetseries.owasp.org/cheatsheets/Authentication_Cheat_Sheet.html (accessed 3 November 2026)
  8. NIST, “NIST Special Publication 800-63B”. https://pages.nist.gov/800-63-3/sp800-63b.html (accessed 3 November 2026)
  9. Cybermalveillance.gouv.fr, “Pourquoi et comment bien gérer ses mots de passe ? - Assistance aux victimes de cybermalveillance”, 23 November 2019. https://www.cybermalveillance.gouv.fr/tous-nos-contenus/bonnes-pratiques/mots-de-passe (accessed 3 November 2026)
  10. MITRE ATT&CK, “Credentials from Password Stores: Password Managers, Sub-technique T1555.005 - Enterprise | MITRE ATT&CK®”. https://attack.mitre.org/techniques/T1555/005/ (accessed 3 November 2026)

Cite this article

Brain, “Zero-Knowledge password managers”, Cyberpedia, 2026. https://startbrain.io/cyberpedia/en/articles/zero-knowledge-password-manager/

BibTeX 
@misc{brain_cp201_en_2026,
  author = {Brain},
  title = {Zero-Knowledge password managers},
  year = {2026},
  howpublished = {Cyberpedia},
  url = {https://startbrain.io/cyberpedia/en/articles/zero-knowledge-password-manager/},
  note = {CC BY 4.0}
}
CC BY 4.0 licence