Could not resolve key encryption credential

[Willem D'Haeseleer]

Hello,

I am trying to configure a SAML SP with the http://www.testshib.org/ IDP
using the onelogin python-saml toolkit
located here:  https://github.com/onelogin/python-saml

When I try to login I get redirected back to my SP but the the IDP fails to
encrypt the assertion.
It gives the following error:

17:55:15.117 - ERROR
[edu.internet2.middleware.shibboleth.idp.profile.saml2.AbstractSAML2ProfileHandler:927]
- Could not resolve a key encryption credential for peer entity:
http://local.origami42.com:8000/metadata/
17:55:15.117 - ERROR
[edu.internet2.middleware.shibboleth.idp.profile.saml2.AbstractSAML2ProfileHandler:289]
- Unable to construct encrypter
org.opensaml.xml.security.SecurityException: Could not resolve key
encryption credential

I included the full error in the idp-process.log file, as well as my
SP metadata file.
I searched trough the archives and found some similar questions, but I
couldn't really make sense of them.

Why can't the IDP encrypt the assertion ?
Am I using an incorrect certificate / public key, should I update the
medata somehow ?

( Sorry for the duplicate email, forgot the subject in the previous one... )
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