Use 'sha256' instead of 'sha' when validating RSA signing supportability

[pavledjo]

In Openssl 3.0.1 in default configuration, jose_server.erl will determine that no RS* algorithms are supported for signing. The reason for this is usage of sha for DigestType when determining RSA signing supportability.

This breaks various flows even though 2 workarounds exist (both of which are not satisfactory enough in our case):

1. Set JOSE crypto_fallback env var to true
2. Allow explicitly RSA+SHA1 signatures in openssl config

I propose we change the DigestType to sha256, since sha1 signature creation will probably be disabled in the future on both RHEL 9 and RHEL 10, based on info from [1].

Currently, SHA1+RSA signature creation is not allowed in OpenSSL configuration on public cloud Alma Linux images. Where the config is hardened to disallow certain signature algorithms. On those machines, example output of JOSE.JWA.supports() is as follows:

...
{:jws,
   {:alg, [“ES256”, “ES384", “ES512”, “HS256", “HS384”, “HS512", “Poly1305”]}} 
....

If we use sha256 to create and validate RSA signing algorithms, the supported list becomes correct:

...
{:jws,
   {:alg,  [“ES256”, “ES384", “ES512”, “HS256", “HS384”, “HS512", “PS256”, “PS384", “PS512”, “Poly1305", “RS256”, “RS384", “RS512”]}} 
....

Setup:

Alma Linux 9.1
OpenSSL 3.0.1
Elixir 1.14.0-otp-25
Erlang 25.0.4
jose 1.11.2

[1] openssl/openssl#17662

[pavledjo]

Hello @potatosalad / @ericmj (sorry if I tagged the wrong people, if so do let me know who I can reach out to); do you have any feedback for the proposed approach? Thanks in advance!

[potatosalad]

Awesome, thank you @pavledjo !

[pavledjo]

Hi @potatosalad, are there are any obstacles to merging this?

[comanjoni]

Hi guys, is this going to be released any time soon? I'm interested into this fix too.

[potatosalad]

Thanks! Will get a new version tagged and released soon.

[pavledjo]

Sorry to bug you @potatosalad, will the release happen anytime soon? :)

[potatosalad]

Sorry to bug you @potatosalad, will the release happen anytime soon? :)

No worries, I apologize for the delayed release. jose 1.11.6 is now published with this fix included.