Information, Computer and Network Security Terms Glossary and Dictionary

Birthday Paradox

Birthday paradox states that the probability that two or more people in a group of 23 share the same birthday is greater than 1/2. For 60 or more people, the probability is greater than 99%. This is called a paradox because that contradicts common intuition, though mathematically true. Calculating this probability (and related ones) is the birthday problem. The mathematics behind it has been used to devise a well-known cryptographical attack named the birthday attack.

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Birthday Paradox