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Ubuntu Archive and CD/USB images complete migration to 4096 RSA signing keys


Enigma machine photo by Alessandro Nassiri [CC BY-SA 4.0], via Wikimedia Commons

Ubuntu Archive and CD/USB image use OpenPGP cryptography for verification and integrity protection. In 2012, a new archive signing key was created and we have started to dual-sign everything with both old and new keys.

In April 2017, Ubuntu 12.04 LTS (Precise Pangolin) will go end of life. Precise was the last release that was signed with just the old signing key. Thus when Zesty Zapus is released as Ubuntu 17.04, there will no longer be any supported Ubuntu release that require the 2004 signing keys for validation.

The Zesty Zapus release is now signed with just the 2012 signing key, which is 4096 RSA based key. The old 2004 signing keys, where were 1024 DSA based, have been removed from the default keyring and are no longer trusted by default in Zesty and up. The old keys are available in the removed keys keyring in the ubuntu-keyring package, for example in case one wants to verify things from old-releases.ubuntu.com.

Thus the signing key transition is coming to an end. Looking forward, I hope that by 18.04 LTS time-frame the SHA-3 algorithm will make its way into the OpenPGP spec and that we will possibly start a transition to 8096 RSA keys. But this is just wishful thinking as the current key strength, algorithm, and hashsums are deemed to be sufficient.
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