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

Bob asked it doesnt matter as long as one of the bits

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Unformatted text preview: nd H(R1,R2,b´) and see which was equal to what he received from Alice. Bit Commitment Using Pseudo-Random-Sequence Generators This protocol is even easier [1137]: (1) Bob generates a random-bit string and sends it to Alice. RB (2) Alice generates a random seed for a pseudo-random-bit generator. Then, for every bit in Bob’s random-bit string, she sends Bob either: (a) the output of the generator if Bob’s bit is 0, or (b) the XOR of output of the generator and her bit, if Bob’s bit is 1. When it comes time for Alice to reveal her bit, the protocol continues: (3) Alice sends Bob her random seed. (4) Bob completes step (2) to confirm that Alice was acting fairly. If Bob’s random-bit string is long enough, and the pseudo-random-bit generator is unpredictable, then there is no practical way Alice can cheat. Blobs These strings that Alice sends to Bob to commit to a bit are sometimes called blobs. A blob is a sequence of bits, although there is no reason in the protocols why it has to be. As Gilles Brassard said, “They could be made out of fairy dust if this were useful” [236]. Blobs have these four properties: 1. Alice can commit to blobs. By committing to a blob, she is committing to a bit. 2. Alice can open any blob she has committed to. When she opens a blob, she can convince Bob of the value of the bit she committed to when she committed to the blob. Thus, she cannot choose to open any blob as either a zero or a one. 3. Bob cannot learn how Alice is able to open any unopened blob she has committed to. This is true even after Alice has opened other blobs. 4. Blobs do not carry any information other than the bit Alice committed to. The blobs themselves, as well as the process by which Alice commits to and opens them, are uncorrelated to anything else that Alice might wish to keep secret from Bob. Previous Table of Contents Next Products | Contact Us | About Us | Privacy | Ad Info | Home Use of this site is subject to certain Terms & Conditions, Copyright © 1996-2000 Earth...
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This note was uploaded on 10/18/2010 for the course MATH CS 301 taught by Professor Aliulger during the Fall '10 term at Koç University.

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