Add support for SHA224

[Wilfred]

Would it be possible to add support for SHA224? This would allow us to depend entirely on ring in the Remacs project.

[moosingin3space]

Seconding this, I'd like to be able to completely get rid of Emacs' private implementation of hash functions and replace it with a better-quality crypto library like ring.

[briansmith]

Hi, I am happy to help you use ring. I'm a bit unsure what to do, because we intentionally don't support SHA-224 because nobody should be using SHA-224. We only support SHA-1 because of some the-internet-would-break-if-we-didn't things use it like Git and OCSP and TLS.

So, first, can you simply not implement SHA-224 in Remacs? Like, just pretend it doesn't exist? That seems ideal to me, not just as a ring contributor, but also as a crypto person in general.

[moosingin3space]

@Wilfred do you know what relies on SHA224?

[briansmith]

It seems like there's not a strong use case for adding this to ring. In the case of Remacs, you can simply use a pure Emacs Lisp implementation of SHA-224 because nothing performance- or security- critical should need to use it. That would already be required for MD5 anyway.