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List:       avispa-users
Subject:    Re: [Avispa-users] problem exchange specification
From:       "Laurent Vigneron" <Laurent.Vigneron () loria ! fr>
Date:       2008-07-31 10:05:12
Message-ID: 20080731120512.63652nhjnc9b1nx4 () horde ! loria ! fr
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Hello Antonio,

> A => B: Data,{SNE,TNE,RandNum,B,h(Data)}.inv(ka),{SNE,ka}_inv(kb)
> The second part tries to represent a kind of certificate
> B => A: {SNE,TNE,RandNum,h(Data)}.inv(kb)

I have some questions about your protocol:
- in the first message, are you sure that the last part is encrypted  
by inv(kb)? this means that A knows the private key of B; usually, we  
write that A encrypts some message with the public key of B, then be  
can decrypt it with its private key (and in your case get ka for  
decrypting the first cypher).
- does B know ka from the beginning, or will he learn it after  
receiving the first message?

> In my protocol, the entity B stores the set {sne,tne,randnum} when he
> receives a message, if B receives more than once this message, he does
> not generates a response message. How can I put this in HSPL?
I do not know how you can model this: when will you know that no copy  
of this message will reach B? do you want to set a time limit?

> I'm getting this attack. It could be related to my previous question.
> In the attack, in the last part it appears {sne.ka}_inv(ka) instead of
> {sne.ka}_inv(kb), why?
About your HLPSL specification, the hash function has been declared as  
a local variable in each role, but it does not have a value: you  
should put it as parameter, and also add it in the intruder knowledge.
And that authentication attack is found because the value of State in  
role alice stays to 2; you should set it to another value when the  
second transition is applied.

Best regards,
Laurent.
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