Hashing is ________.

• A. reversible
• B. repeatable
• C. Both A and B
• D. Neither A nor B

Answer: (B)

Hashing relies on a deterministic function: the same input will always produce the same hash output when you use the same algorithm. That repeatable, or deterministic, nature is what makes hashes useful for data integrity checks—hash the data again, and if nothing changed, you’ll get the identical value. However, hashes are not reversible; you can’t reliably recover the original input from the hash alone. In cryptographic hashing, in fact, reversing the process is what we try to prevent. Because of that one-way characteristic, the option describing reversibility is incorrect, and the statement that best fits hashing is that it is repeatable.