Friday, 26 August 2011

Sign Here

I would not want to describe the paperwork that goes with University life as something out of
Terry Gilliam's Brazil or Yes Minister.

It would be ill-advised: I haven't completed this month's NGS/B/11347/2(a) (permission to use ironic over-exaggeration within a blog) and submitted it to the appropriate authorities.

Depending on how deeply your institution loves its paperwork, there will be forms to be complete when claiming travel costs, or buying a new HPC system, or obtaining a replacement biro. Inevitably, somebody else needs to sign these forms to show that there has been due diligence and that the trip to Didcot, million pound compute cluster or cheap plastic pen are fully justified.

Somebody else isn't just anybody. When you present your form to the powers-that-be, the powers-that-be will carefully compare the signature with their collection of scribbles from the great-and-the-good.

Only when you have the right name in the right place on the right form will you will receive a new pen and a firm lecture about being more careful in future.

As we have said on a number of occasions, grid security is built on chains of trust. It also relies on the right signature being used in the right place. In our case, these are digital signatures represented by X.509 certificates rather than the spiders-web-on-acid scrawl of a senior University manager.

A certificate in your local list of trusted certificates - typically in /etc/grid-security/certificates - can be accompanied by a file defining its signing-policy. You can see some examples of signing policy files in the UK eScience Certification Authority pages on the website.

The signing policy is particularly influential at the very far end of the chain of trust: the root certificates. The private key associated with root certificates are kept in a Very Safe Place and are taken out only to sign the certificates of Certification Authorities (CAs).

CAs sign the certificates for the rest of us. The UK has two CA's - the main eScience CA and a SARoNGS CA.

Over the last weeks, thanks to the efforts of the dragon-slayers at the Software Sustainability Institute, we finally found out why certificates from our 'SARoNGS' CA were being rejected by the NGS's Workload Management Service.

There was nothing wrong with the certificates themselves.

The SSI developers quickly identify problems with the SARoNGS Certificate Revocation List (CRL) - a list of known-bad certificates that CA's should distribute.

SARoNGS certificates are designed to be short-lived - they expire before anyone gets a chance to do something bad with them - and the revocation list is empty. But all revocation lists - even empty ones - have expiry dates and ours had, unfortunately, gone stale.

Updating the CRL was comparatively easy but it did not solve the problem. The root cause of turned out to be the root certificate's signing policy.

The problem is that there are two signing policies - depending on whether you consider SARoNGS certificates acceptable.

SARoNGS certificates can be obtained using only a UK academic username and password whereas a full eScience certificates requires photo ID and a visit to your local Registration Authority.

The International Grid Trust Federation (IGTF) is responsible for ensuring that certificates are being created and managed in a trust-worthy way. It has strict rules on what constitutes sufficient proof of a users identity and - not to put too fine a point on it - an academic username and password are simply not good enough.

So the signing policy within the IGTF's bundle of UK eScience certificate information does not currently match the version we distribute. The IGFT version will not permit the eScience root to sign for the SARoNGS CA.

The root cause was a misplaced update that installed the IGTF version of the eScience root signing-policy - rather than the NGS's own.

We should have had the 'IGTF+' certificates - a modified version of the IGTF's certificate collection maintained by the NGS blogs' very own Jens Jensen, and incorporating the NGS's signing policy and some additional certificates.

The IGTF+ certificates are available in a number of formats from Jens's avowedly Web-1.0 certificate repository webpage.

[With thanks to James Perry, Steve Crouch and Rob Baxter of the Software Sustainability Institute]

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