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659 decrypt the corresponding messages. |
659 decrypt the corresponding messages. |
660 |
660 |
661 Now the big question is, why on earth does this splitting |
661 Now the big question is, why on earth does this splitting |
662 of messages in half and additional message exchange help |
662 of messages in half and additional message exchange help |
663 with defending against person-in-the-middle attacks? Well, |
663 with defending against person-in-the-middle attacks? Well, |
664 let's try to be such an attacker. As before we intercept |
664 let's try to be an attacker. As before we intercept |
665 the messages where public keys are exchanged and inject |
665 the messages where public keys are exchanged and inject |
666 our own. |
666 our own. |
667 |
667 |
668 \begin{center} |
668 \begin{center} |
669 \begin{tabular}{ll@{\hspace{2mm}}l} |
669 \begin{tabular}{ll@{\hspace{2mm}}l} |
770 together). So the only option is to send $M_2$. |
770 together). So the only option is to send $M_2$. |
771 |
771 |
772 With this the protocol has ended. $E$ was able to decrypt all |
772 With this the protocol has ended. $E$ was able to decrypt all |
773 messages, but what messages did $A$ and $B$ receive and from |
773 messages, but what messages did $A$ and $B$ receive and from |
774 whom? Do you notice that $A$ and $B$ will find out that |
774 whom? Do you notice that $A$ and $B$ will find out that |
775 something strange has happened and probably not talk on this |
775 something strange is going on and probably not talk on this |
776 channel anymore? I leave you to think about it. |
776 channel anymore? I leave you to think about it. |
777 |
777 |
778 Recall from the beginning that a person-in-the middle |
778 Recall from the beginning that a person-in-the middle |
779 attack can easily be mounted at the key fob and car |
779 attack can easily be mounted at the key fob and car |
780 protocol unless we are careful. If you look at actual |
780 protocol unless we are careful. If you look at actual |