MATH 456 Final: MATH456 ROSENBERG-J SPRING2013 0101 FINAL SOL

• School: University of Maryland
• Department: Mathematics
• Course: MATH 456
• Professor: All

Document Summary

Suppose the plaintexts were x0, , xm. This now gives m n-bit strings to work with. If one can guess the contexts of at least part of one message (which for convenience we take to be x0), then we immediately get the corresponding parts of the other messages. Of course the method is not guaranteed to work since if the messages are all random strings of n bits, then there is still no way to guess anything. If the values of n are really chosen at random, then this is like the birthday problem, with 104 people and 106 possible birthdays. Since 104 is much bigger than 106 = 103, a coincidence is almost guaranteed. More precisely (including this is optional), the chance of a coincidence is. 1 p (no coincidence) = 1 yj=0. 1 e 108/(2 106) = 1 e 50 1. But choosing the value of n at random is crucial here.