Changes to default password hashing algorithm and umask settings

Sept. 22, 2023 - David Runge

With shadow >= 4.14.0, Arch Linux's default password hashing algorithm changed from SHA512 to yescrypt.

Furthermore, the umask settings are now configured in /etc/login.defs instead of /etc/profile.

This should not require any manual intervention.

Reasons for Yescrypt

The password-based key derivation function (KDF) and password hashing scheme yescrypt has been chosen due to its adoption (readily available in libxcrypt, which is used by pam) and its stronger resilience towards password cracking attempts over SHA512.

Although the winner of the Password Hashing Competition has been argon2, this algorithm is not yet available in libxcrypt (attempt one, attempt two).

Configuring yescrypt

The YESCRYPT_COST_FACTOR setting in /etc/login.defs is currently without effect, until pam implements reading its value. If a YESCRYPT_COST_FACTOR higher (or lower) than the default (5) is needed, it can be set using the rounds option of the pam_unix module (i.e. in /etc/pam.d/system-auth).

General list of changes

  • yescrypt is used as default password hashing algorithm, instead of SHA512
  • pam honors the chosen ENCRYPT_METHOD in /etc/login.defs and does not override the chosen method anymore
  • changes in the filesystem (>= 2023.09.18) and pambase (>= 20230918) packages ensure, that umask is set centrally in /etc/login.defs instead of /etc/profile