[OpenID] Nonces generated by the server?

[Johannes Ernst]

It makes it easier to implement IdP-initiated SSO, i.e. a shorter  
redirect dance.


On Mar 31, 2009, at 14:28, Martin Atkins wrote:

>
> I was idly reading the OpenID spec today and was reminded that the  
> OpenID spec has the server generate a response nonce, rather than it  
> being generated by the consumer.
>
> This seems strange to me, because in order to prevent replay it  
> requires the consumer to remember all nonces that it has seen  
> recently. If the consumer generated the nonce, then it would only  
> need to retain state of nonces that it has issued, which is  
> conceptually simpler.
>
> I note that over in OAuth land they have the consumer generate the  
> nonce rather than the server.
>
> Is there a specific security reason why the server generates the  
> nonce in OpenID, or was this just an arbitrary decision?
>
> I'm also somewhat curious about how many OpenID consumers actually  
> do nonce checking. Net::OpenID::Consumer for Perl actually ignores  
> the nonce altogether and implements its own timestamp checking due  
> to legacy code for OpenID 1.1, and seems to be vulnerable to replay  
> for up to 30 seconds after a positive assertion. Are *any* RPs  
> actually checking nonces to prevent replay during the timestamp  
> window?
>
>
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