A collision attack occurs when an attacker finds two distinct inputs that hash to the same output. This undermines the uniqueness property of a hash function, which is critical for tasks like verifying the integrity of data or digital signatures. Downgrade attacks involve forcing a system to abandon a higher security level in favor of a lower, less secure state. Birthday attacks exploit the mathematics behind the birthday problem in probability theory to find collisions in hash functions, but do not necessarily find two distinct inputs that produce the same hash output; they are just more likely to find a collision given a certain number of attempts. Collision attacks directly find the two distinct inputs.