{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

applied cryptography - protocols, algorithms, and source code in c

The chance of her fooling him in two rounds is 25

Info icon This preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: et none of the questions or answers gives Victor any information about Peggy’s information—only about her knowledge of it. Basic Zero-Knowledge Protocol Jean-Jacques Quisquater and Louis Guillou explain zero-knowledge with a story about a cave [1281]. The cave, illustrated in Figure 5.1, has a secret. Someone who knows the magic words can open the secret door between C and D. To everyone else, both passages lead to dead ends. Peggy knows the secret of the cave. She wants to prove her knowledge to Victor, but she doesn’t want to reveal the magic words. Here’s how she convinces him: (1) Victor stands at point A. (2) Peggy walks all the way into the cave, either to point C or point D. (3) After Peggy has disappeared into the cave, Victor walks to point B. (4) Victor shouts to Peggy, asking her either to: (a) come out of the left passage or (b) come out of the right passage. (5) Peggy complies, using the magic words to open the secret door if she has to. (6) Peggy and Victor repeat steps (1) through (5) n times. Assume that Victor has a camcorder and records everything he sees. He records Peggy disappearing into the cave, he records when he shouts out where he wants Peggy to come out from, and he records Peggy coming out. He records all n trials. If he showed this recording to Carol, would she believe that Peggy knew the magic words to open the door? No. What if Peggy and Victor had agreed beforehand what Victor would call out, and Peggy would make sure that she went into that path. Then she could come out where Victor asked her every time, without knowing the magic words. Or maybe they couldn’t do that. Peggy would go into one of the passages and Victor would call out a random request. If Victor guessed right, great; if he didn’t, they would edit that trial out of the camcorder recording. Either way, Victor can get a recording showing exactly the same sequence of events as in a real proof where Peggy knew the magic words. Figure 5.1 The zero-knowledge cave. This shows two things. One, it is impossible for Victor to convince a third party of the proof’s validity. And two, it proves that...
View Full Document

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern