Fedora 35 Looking To Use Yescrypt For Hashing User Passwords

Written by Michael Larabel in Fedora on 9 June 2021 at 07:00 AM EDT. 14 Comments
Adding to the list of planned improvements for Fedora 35 is switching to make use of Yescrypt for hashing of user passwords.

Fedora developers are looking at using Yescrypt as the default hashing mode for new user passwords within /etc/shadow. While SHA256/SHA512 haven't yet been broken as common used today for Linux account password hashing, Yescrypt would beef up the security.

As explained on the Openwall project site for Yescrypt, "yescrypt is a password-based key derivation function (KDF) and password hashing scheme. It builds upon Colin Percival's scrypt... Like it or not, password authentication remains relevant (including as one of several authentication factors), password hash database leaks happen, the leaks are not always detected and fully dealt with right away, and even once they are many users' same or similar passwords reused elsewhere remain exposed. To mitigate these risks (as well as those present in other scenarios where password-based key derivation or password hashing is relevant), computationally expensive (bcrypt, PBKDF2, etc.) and more recently also memory-hard (scrypt, Argon2, etc.) password hashing schemes have been introduced. Unfortunately, at high target throughput and/or low target latency their memory usage is unreasonably low, up to the point where they're not obviously better than the much older bcrypt (considering attackers with pre-existing hardware). This is a primary drawback that yescrypt addresses. Most notable for large-scale deployments is yescrypt's optional initialization and reuse of a large lookup table, typically occupying at least tens of gigabytes of RAM and essentially forming a site-specific ROM. This limits attackers' use of pre-existing hardware such as botnet nodes. yescrypt's other changes from scrypt additionally slow down GPUs and to a lesser extent FPGAs and ASICs even when its memory usage is low and even when there's no ROM, and provide extra knobs and built-in features."

Thus a change proposal has been filed that would make use of Yescrypt for new user password hashing on the distribution. Besides Fedora, ALT Linux, Debian Testing, and Kali Linux are among other distributions already making use of Yescrypt.

So far the feedback around this change to use Yescrypt has been fairly positive and another step forward for improving security.
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