timestamp based protocol

In a session-key distribution protocol, Bob should check that:
1) "tB - tA" is in the acceptance window range.
2) tA is different from all other received timestamps.

I don't understand point 2!

What could do an enemy without point 2??

(I ask that because I am a student and my book is not very clear at this
point..)

Thanks..


.

Relevant Pages

  • Re: Contact
    ... Warum muss ich jetzt an "enemy mine" denken? ... _Credo quia absurdum est._ ... Prev by Date: ...
    (de.rec.sf.misc)
  • Re: Torture and Murder of prisoners
    ... Given the ideology of those who want the pictures released, I'd say it's to incite the enemy. ... (ACLU, Amnesty International, Human Rights Watch, etc.) ... Prev by Date: ...
    (sci.military.naval)
  • Re: OT: Begging for Standards after BushCo Chaos
    ... Teaching them "lessons" neither impresses nor frightens the enemy. ... Prev by Date: ...
    (rec.gambling.poker)
  • Re: NEW LAO LIBERATION ALLIANCE
    ... These groups can't overthrow the communist party cuz they have no plan ... and they are too stupid to know who is their enemy. ... Prev by Date: ...
    (soc.culture.hmong)