Master Password (algorithm)
|Original author(s)||Maarten Billemont|
|Initial release||June 15, 2012|
2.3 / April 19, 2015
|Operating system||Microsoft Windows and Unix-like, including OS X, iOS and Android|
|License||GNU General Public License|
Master Password is an algorithm designed by Maarten Billemont for creating unique passwords in a reproducible manner. It differs from traditional password managers in that the passwords are not stored on disk or in the cloud, but are recreated every time by using information entered by the user; most importantly, their full name, a master password, and a unique name for the service the password is intended for.
By not storing the passwords anywhere, this approach tries to make it harder for attackers to steal or intercept them. It also removes the need for synchronization between devices, and backups of potential password databases. It also removes the risk of a data breach. They are sometimes called sync-less password managers.
The algorithm involves the following parameters:
- name: The user's full name, used as a salt. The user's full name is chosen as it provides a sufficiently high level of entropy, while being unlikely to be forgotten.
- master_password: The secret used for generating the master key.
- site_name: A unique name for the service the password is intended for. Usually, the bare domain name is a good choice.
- counter: An integer that can be incremented when the service requests a new password. By default, it is 0.
- password_type: The password type defines the length and the constitution of the resulting password, see below.
Master key generation
The master key is a global 64-byte secret key generated from the user's secret master password and salted by their full name. The salt is used to avoid attacks based on rainbow tables. The scrypt algorithm, an intentionally slow key derivation function, is used for generating the master key to make a brute-force attack infeasible.
salt = "com.lyndir.masterpassword" + length(name) + name master_key = scrypt(master_password, salt, 32768, 8, 2, 64)
Template seed generation
The template seed is a site-specific secret in binary form, generated from the master key, the site name and the counter using the HMAC-SHA256 algorithm. It is later converted to a character string using the password templates. The template seed makes every password unique to the website and to the user.
seed = hmac_sha256(master_key, "com.lyndir.masterpassword" + length(site_name) + site_name + counter)
The binary template seed is then converted to one of six available password types. The default type is the Maximum Security Password, others can be selected if the service's password policy does not allow passwords of that format:
- Maximum Security Password (20 ASCII printable characters)
- Long Password (14 ASCII printable characters)
- Medium Password (8 ASCII printable characters)
- Short Password (4 ASCII printable characters)
- Basic Password (8 alphanumeric characters)
- PIN (4 digits)
- An app for iOS. The iOS implementation was first released in 2012.
- An app for Mac OS X
- An app for Android
- A Graphical desktop application written in Java
- A command-line application written in C
- A browser plugin for Firefox and Chromium-based browsers
- Billemont, Maarten. "The Master Password Algorithm". Archived from the original on December 9, 2017. Retrieved 8 May 2015.
- "License file of the MasterPassword repository". Retrieved 15 May 2015. CS1 maint: discouraged parameter (link)
- Billemont, Maarten. "Release 1.0.0". Retrieved 15 May 2015. CS1 maint: discouraged parameter (link)
- Masterpassword's Firefox add-on
- Masterpassword's Chrome plugin
- Billemont, Maarten. "Master Password Homepage". Retrieved 15 May 2015. CS1 maint: discouraged parameter (link)