What happens during a collision in cryptography?

In cryptography, a collision occurs when two distinct inputs produce the same output or digest in a hashing function. This is significant because one of the fundamental properties of a secure hashing algorithm is that it should be infeasible to find two different inputs that result in the same hash. Such collisions can undermine the integrity and authenticity of data. If an attacker can create a different message that has the same hash as a legitimate one, they could substitute the original message with the forged one without detection.

While the other options describe different scenarios, they do not capture the essence of what a collision means in cryptographic terms. Sending data without encryption does not relate to hash functions and their properties. Similarly, the idea that a message is permanently lost does not pertain to the concept of a collision; rather, it describes issues with data transmission or storage. Thus, the identification of two messages producing the same digest accurately characterizes a collision in cryptography.