16-01-2014, 12:10 PM
Birthday attack
Birthday attack.doc (Size: 43.5 KB / Downloads: 23)
A birthday attack is a type of cryptographic attack that exploits the mathematics behind the birthday problem in probability theory. This attack can be used to abuse communication between two or more parties. The attack depends on the higher likelihood of collisions found between random attack attempts and a fixed degree of permutations (pigeonholes), as described in the birthday problem/paradox.
Understanding the problem
As an example, consider the scenario in which a teacher with a class of 30 students asks for everybody's birthday, to determine whether any two students have the same birthday (corresponding to a hash collision as described below; for simplicity, ignore February 29). Intuitively, this chance may seem small. If the teacher picked a specific day (say September 16), then the chance that at least one student was born on that specific day is , about 7.9%. However, the probability that at least one student has the same birthday as any other student is around 70% (using the formula for n = 30).