brew/docs/Checksum_Deprecation.md
Issy Long 31d7bcc583
Add a last_reviewed_date to docs metadata
- At the AGM we formed an ad-hoc documentation working group.
- One of our ideas was that we should have a last reviewed date for
  documentation, so that we can periodically implement a review
  mechanism (GitHub Actions posts to Slack for a regular documentation
  outdatedness check?) to track how old docs are and ensure they're
  still relevant.
- This is a first step towards that goal, by adding a `last_review_date`
  to the metadata of all docs with a date of earlier than Homebrew's
  inception because everything needs reviewing so that we start from a
  good base!
2025-02-03 11:56:07 +00:00

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Markdown

---
last_review_date: "1970-01-01"
---
# MD5 and SHA-1 Deprecation
In early 2015 Homebrew started the process of deprecating _SHA1_ for package
integrity verification. Since then formulae under the Homebrew organisation
have been migrated to use _SHA-256_ for verification; this includes both source
packages and our precompiled packages (bottles).
Homebrew has since stopped supporting _SHA1_ and _MD5_ entirely.
_MD5_ checksums were removed from core formulae in 2012 and as of April 2015
installing a formula verified by _MD5_ is actively blocked.
We removed _SHA1_ support in **November 2016**,
21 months after we started warning people to move away from it for verification.
This is enforced in the same way _MD5_ is, by blocking the installation of that
individual formula until the checksum is migrated.
This means custom taps, local custom formulae, etc. need to be migrated to use
_SHA-256_ before you can install them.