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Category > Computer Science Posted 23 Sep 2017 My Price 6.00

public-key certificate formats,

In addition to providing a standard for public-key certificate formats, X.509 specifies an authentication protocol. The original version of X.509 contains a security flaw. The essence of the protocol is as follows.

A→ B: A {tA, rA, IDB}

B→ A: B {tB, rB, IDA, rA}

A→ B: A {rB}

Where ta and tb are timestamps, raand rb are nonces and the notation X {Y} indicates that the message Y is transmitted, encrypted, and signed by X. The text of X.509 states that checking timestamps tAand tBis optional for three-way authentication. But consider the following example: Suppose A and B have used the preceding protocol on some previous occasion, and that opponent C has intercepted the preceding three messages. In addition, suppose that timestamps are not used and are all set to 0. Finally, suppose C wishes to impersonate A to B. C initially sends the first captured message to B:

C→ B: A {0, rA, IDB}

B responds, thinking it is talking to A but is actually talking to C:

B → C: B {0, r’B, IDA, rA}

C meanwhile causes A to initiate authentication with C by some means. As a result, A sends C the following:

A→  C: A {0, rA’ , IDC}

C responds to A using the same nonce provided to C by B:

C→ A: C {0, r’B, IDA, r’A}

A responds with

A→ C: A {r’B}

This is exactly what C needs to convince B that it is talking to A, so C now repeats the incoming message back out to B.

C → B: A {r’B}

So B will believe it is talking to A whereas it is actually talking to C. Suggest a simple solution to this problem that does not involve the use of timestamps.

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Maurice Tutor
(5)
Status NEW Posted 23 Sep 2017 09:09 AM My Price 6.00

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