Which statement describes preimage resistance?

Which statement describes preimage resistance?

• A. It is computationally infeasible to determine the original input from the hash code.
• B. It is easy to invert the hash to recover the input.
• C. It guarantees unique hashes for all inputs.
• D. It requires a secret key to generate the hash.

Answer: (A)

Preimage resistance means that, given a hash value h, it should be computationally infeasible to find any input x such that H(x) = h. The statement that matches this exactly is that it is computationally infeasible to determine the original input from the hash code. This property ensures that you can verify data integrity via the hash without being able to reverse-engineer the original data. It’s not about getting a unique hash for every input (that relates to collisions) and not about using a secret key (that would be a keyed hash or MAC).

Preimage resistance means that, given a hash value h, it should be computationally infeasible to find any input x such that H(x) = h. The statement that matches this exactly is that it is computationally infeasible to determine the original input from the hash code. This property ensures that you can verify data integrity via the hash without being able to reverse-engineer the original data. It’s not about getting a unique hash for every input (that relates to collisions) and not about using a secret key (that would be a keyed hash or MAC).