[security] OpenID Security Best Practices Doc

[Andrew Arnott]

Hi Allen,

Yes, the RP nonces are vulnerable to PREplay attacks. But not REplay
attacks. That's what the nonce is there to protect in the first place,
after all.

On Monday, June 8, 2009, Allen Tom <atom at yahoo-inc.com> wrote:
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> Hi Andrew,
>
> Are the RP's nonces vulnerable to MITM attacks? For instance, if the
> attacker was able to sniff the nonce in the RP's return_to, then
> presumably, the attacker would be able to replay it?
>
> I guess tying the nonce to the browser's IP address would be sufficent,
> although if there's a MITM, the attacker presumably controls the IP
> address as well.
>
> Allen
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> Andrew Arnott wrote:
> Yes, DotNetOpenAuth
> RPs attach their own nonces to their return_to's when communicating
> with 1.0 OPs.  It would be a simple matter to expand the scenarios
> it activates this behavior for if necessary.
>
>
>   --
> Andrew Arnott
> "I [may] not agree with what you have to say, but I'll defend to the
> death your right to say it." - S. G. Tallentyre
>
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>   On Mon, Jun 8, 2009 at 4:47 PM, John Bradley
>   <jbradley at mac.com> wrote:
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>     The other approach that has been used to secure 1.1
> RP's is to place a signed nonce in the nonce in the return_to URI.
> The RP verifies its own sig.
>
>
>     I believe this is an option in DotNetOpenAuth for openID as
> well.
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>     This removes the need for the RP to synchronize data across
> servers.  This assumes properly configured load balancers though.
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>     That is one other approach.
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>     John B.
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>     On 8-Jun-09, at 7:35 PM, Allen Tom wrote:
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>        Hi Johannes,
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> My personal opinion is that if HTTPS is used for the entire protocol
> flow, including the RP's return_to URL, then the RP should be able to
> verify that the timetamp in the nonce is current, to within a few
> minutes, as opposed to having to verify that the entire nonce is truly
> unique.
>
> Allen
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> Johannes Ernst wrote:
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> On Jun 8, 2009, at 15:50, Allen Tom wrote:
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>           6)  Pull the replay warning into its
> own bullet, and mention the use of a timestamp to bound the time nonces
> must be stored for.
>
> [atom] Also a good point. On a related note, many large globally
> distributed RPs may have a hard time implementing nonces as per the
> OpenID spec, as it's technically tricky to globally replicate data,
> especially if it needs to be replicated very quickly. In practice, RPs
> may only find it practical to verify that the timestamp is "current" as
> opposed to actually verifying that the nonce is can only be used once.
>
>
> In this case, do these mythical "globally distributed RPs" have a
> better approach for avoiding replay attacks or do they simply swallow
> that risk because no better approach is known.
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> Just wondering ...
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> Johannes Ernst
> NetMesh Inc.
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>          http://netmesh.info/jernst
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-- 
--
Andrew Arnott
"I [may] not agree with what you have to say, but I'll defend to the
death your right to say it." - S. G. Tallentyre