IdP v4.0.1 issues with CBC relying-party overrides and SPs with cipher-suite metadata

Robert Bradley robert.bradley at
Thu Nov 12 17:25:48 UTC 2020

On 12/11/2020 14:57, Cantor, Scott wrote:
> The security configuration you're talking about doesn't disallow GCM,
> it simply sets the default to CBC when there is no guidance. The
> metadata says GCM is favored, so the IdP uses it. Actually
> disallowing GCM would require building security configuration beans
> to explicitly enumerate only CBC algorithms or disallow GCM in that
> particular configuration.

That would definitely explain what I was seeing.  I can look into 
building such a bean later, but it'll be easier to fix the metadata at 

> Unless this is a federation supplying the metadata for the SP (in
> which case I'd contact the federation), a much simpler fix is to
> follow best practice and never trust remote metadata in the first
> place, so it can be fixed as required.

These particular SPs are federation-sourced rather than remote metadata, 
so I was expecting a bit of a delay for changes to propagate through. 
Our traditional position has always been to require third-party SPs to 
supply metadata via eduGAIN or the UK AMF, although today's SaaS 
providers have made that trickier to enforce...  For those, we have had 
to resort to local metadata copies for just that reason.

Dr Robert Bradley
Identity and Access Management Team, IT Services, University of Oxford
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