The mailing list for users of the eduroam Configuration Assistant Tool (CAT)

[Alan Cox - UKRI <Alan.Cox AT ukri.org>]

> I don't know a huge amount about the inner workings of the different 
> algorithms

I know even less, but a look at 
https://www.w3.org/TR/xmlenc-core/#sec-RSA-OAEP suggests that the same 
encryption is being used in the two cases.

"#rsa-oaep-mgf1p identifier defines the mask generation function as the fixed 
value of MGF1 with SHA1"

Whereas "#rsa-oaep identifier defines the mask generation function using the 
optional xenc11:MGF element", and in the diffs you give, that element gives 
the URI http://www.w3.org/2009/xmlenc11#mgf1sha1, which is MGF1 with SHA1.

So, the algorithm is the same, just identified differently.

Which is not to say that this isn't the cause of the problem.

Alan.

-----Original Message-----
From: cat-users-request AT lists.geant.org <cat-users-request AT lists.geant.org> 
On Behalf Of Matthew Slowe
Sent: 06 August 2020 10:47
To: cat-users AT lists.geant.org
Subject: Re: [[cat-users]] Unable to authenticate


> On 6 Aug 2020, at 10:08, Alan Cox - UKRI <Alan.Cox AT ukri.org> wrote:
>
> I've just experienced what seems to be the same error, though with a 
> Shibboleth 3.4.6 IdP - https://nerckwshibba.nerc.ac.uk/idp/shibboleth.

Our 3.4.6 IdP is also now seeing the same thing - as is the new v4 IdP.

Comparing the assertion for CAT with a "known good" assertion (against an SP 
which doesn't assert any algorithm requirements), I note these differences:

--- ref.xml2020-08-06 10:38:45.000000000 +0100
+++ cat.xml2020-08-06 10:38:56.000000000 +0100
@@ -4,8 +4,9 @@
     <xenc:EncryptionMethod xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"; 
Algorithm="http://www.w3.org/2001/04/xmlenc#aes128-cbc"/>
     <ds:KeyInfo xmlns:ds="http://www.w3.org/2000/09/xmldsig#";>
       <xenc:EncryptedKey xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"; 
Id="id" Recipient="sp-entityid">
-        <xenc:EncryptionMethod 
xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"; 
Algorithm="http://www.w3.org/2001/04/xmlenc#rsa-oaep-mgf1p";>
+        <xenc:EncryptionMethod
+ xmlns:xenc="http://www.w3.org/2001/04/xmlenc#";
+ Algorithm="http://www.w3.org/2009/xmlenc11#rsa-oaep";>
           <ds:DigestMethod xmlns:ds="http://www.w3.org/2000/09/xmldsig#"; 
Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
+          <xenc11:MGF xmlns:xenc11="http://www.w3.org/2009/xmlenc11#";
+ Algorithm="http://www.w3.org/2009/xmlenc11#mgf1sha1"/>
         </xenc:EncryptionMethod>
       </xenc:EncryptedKey>
     </ds:KeyInfo>


I don't know a huge amount about the inner workings of the different 
algorithms, but I do wonder if SimpleSAMLphp doesn't support "rsa-oaep" but 
does support "rsa-oaep-mgf1p" but, because the first one is listed first it's 
using that?

--
Matthew Slowe
Technical Specialist - Trust & Identity, Jisc

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