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LCG-ROLLOUT  September 2013

LCG-ROLLOUT September 2013

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Subject:

Re: Proxy renewal question

From:

Jan Just Keijser <[log in to unmask]>

Reply-To:

LHC Computer Grid - Rollout <[log in to unmask]>

Date:

Thu, 19 Sep 2013 18:03:15 +0200

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (105 lines)

Hi,

Maarten Litmaath wrote:
> Hallo Jan Just,
>
>>>> can the WMS renew a proxy from a credential with a passphrase on 
>>>> the MyProxy server?
>>>
>>> No, by design!
>>>
>> where is this specified?
>
> It has been like that from the very first of our grid projects;
> we might find this documented in EDG/EGEE design documents,
> but think about it: how would a pass phrase help in this case?
>
> You would have to inform all entities that need to renew or
> retrieve a proxy from the MyProxy server: how do you do that,
> in a secure way?
>
> Sure, the WMS could be told the pass phrase at job submission or
> proxy delegation time, but do you actually _want_ someone's WMS
> to know the password?!  What if the machine gets compromised?
>
> Long ago the grid projects came up with a different way:
> make the WMS a trusted _renewer_ of proxies.
> There are 3 authorization steps required for that to work:
>
> 1. The WMS must authenticate with its host cert.
> 2  Its host DN must be registered in the user-supplied MyProxy
>    server as a trusted renewer.
> 2. The WMS must present the proxy to be renewed while that proxy
>    is still _valid_.
>
> There are other acceptable ways for a MyProxy server to be used
> and some services (e.g. Nagios) do so, but the WMS can only do
> what we just described.
>


>> The system (upload a passphrase protected robot cert generated proxy 
>> to a MyProxy server)
>> has been in operation for 4 years or more and only recently this 
>> problem popped up. Is
>> this behaviour new?
>
> No, but there appears to have been some confusion; see below.
>
>>>> We have a user that uses a robot certificate which stores a 
>>>> credential on the MyProxy
>>>> server. This credential is protected with a passphrase.
>>>
>>> Why?!
>> the robot token is located in a protected server room on an isolated 
>> well-controlled
>> machine. A proxy is generated every 24 hours and uploaded using a 
>> well known password (and
>
> Aha, a well known password...  Understandable, but not needed when
> the MyProxy server is used better.
>
>> using "-d" ) to the MyProxy server.
>> The portal host on which the proxy is needed grabs  a proxy using 
>> this "well-known" password.
>> This has been working for nearly 4 years - could be we just got lucky 
>> during those 4
>> years, but where was it specified that you cannot do this?
>
> You can do _that_, but it is not what this discussion was about!
>
> The question was: can a _WMS_ renew a proxy protected with a pass phrase?
> Answer: no, by design.
>

I wasn't clear in my previous email: what I meant was:

can a WMS renew a proxy from a MyProxy server that was uploaded with a 
passphrase? I'm not saying the WMS would know the passphrase, but as the 
WMS is a trusted renewer it may not need the passphrase at all.

We've now changed the way the proxy is uploaded to the MyProxy server to 
use a username and password; the WMS seems to upload its own proxy to 
the MyProxy store, so hopefully the renewal process now works.


Steven Burke wrote:
> I don't understand what you mean by "well-known" - a) if it's well-known how does it add any security, and b) how you you expect the WMSes to know it? I also don't understand why you would do it every 24 hours - the whole point of myproxy is that it can hold long-lived proxies.

The *reason* for using a passphrase is that if  you do not specify a 
passphrase and you want to use DN-based retrieval (i.e. "-d") then you 
must have a valid proxy or cert/key pair on the "retriever" host. If the 
retriever host is down for a longer period of time then its proxy 
expires and you have to manually jumpstart the process by sending a new 
proxy via some other route to the retrieving host.

I agree that it's not necessary to do this every 24 hours, I used to do 
it every 48 hours but there was a VOMS-related issue at the time, which 
I avoided by doing it every 24 hours.

cheers,

JJK / Jan Just Keijser
Nikhef
Amsterdam

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