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This question related to attack on the LMAP++ the result of extracting ID from the messages. In Passive Attack on RFID LMAP++ Authentication Protocolm, page 188

ID = C ⊕ IDS ⊕ A ⊕ B

While in this paper Security Analysis of LMAP++, an RFID Authentication Protocol

ID = C ⊕ IDS ⊕ A ⊕ B ⊕ IDs ⊕ IDs ⊕ IDs

where(IDs = PID)

Which one is correct?

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    $\begingroup$ 1. It'd help if you identified exactly where in the paper the second equation appears, as it doesn't appear in the form you have listed here. 2. It'd be nice to provide full citations for the papers (title, author, where published) so that if the links stop working readers can still tell what you are referring to. 3. Your link to the first paper looks like a pirated copy of a Springer LNCS volume, i.e., copyright infringement. Speaking purely for myself, that seems sketchy. Do you want to support that kind of thing? (Related: meta.stackexchange.com/q/49427/160917.) $\endgroup$
    – D.W. ♦
    Nov 21, 2015 at 7:00
  • $\begingroup$ I can not tell if this is a computer science question, or a security engineering question that happens to use formal notation. (Are you aware of Information Security?) $\endgroup$
    – Raphael
    Nov 21, 2015 at 11:09
  • $\begingroup$ @Raphael This is definitely a computer science question. The paper was published in LNCS after all. Information Security might entertain this question but there's a good chance they'd consider it too theoretical and would bounce it here or to Cryptography. $\endgroup$
    – Gilles 'SO- stop being evil'
    Nov 21, 2015 at 12:27
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    $\begingroup$ Please explain your notations. What are ID, C, IDS, etc? What is ⊕ in this context? $\endgroup$
    – Gilles 'SO- stop being evil'
    Nov 21, 2015 at 12:28

1 Answer 1

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You didn't copy the second equation correctly from the second paper. The equation in the second paper is

eqn2

In your notation, this is

ID =  A ⊕ B ⊕ C ⊕ IDs ⊕ IDs ⊕ IDs

Note: the paper has 3 occurrences of IDs, not 4 occurrences; your post has 4 occurrences. This makes all the difference in the world.

Of course, IDs ⊕ IDs ⊕ IDs = IDs (follows since X ⊕ X = 0 holds for all X). Therefore, the second equation is equivalent to

ID =  A ⊕ B ⊕ C ⊕ IDs

which is equivalent to the first equation.

Thus, if you accurately copy down the equation from the equation from the second paper, you'll find that it is equivalent to the equation from the first paper.

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