The birthday attack is a cryptographic attack based on the birthday paradox, or the probability of a group of people having the same birthday. The use of the theory of the birthday paradox improves the probability of creating a hash collision. Watch this video to understand the mathematics behind the birthday paradox. Do not be concerned with learning the mathematics. Instead, pay attention to how the probability increases as the number of people in the room increase, and how the brute attack effort decreases with the birthday paradox.