Which statements about hashing are correct? i. It is a one-way functionii. Used for password storageiii. Can be reversed with the correct keyiv. Ensures data integrity

Question

BlackTom AI · Accepted Answer

Hash functions are designed to be one-way, deterministic transforms that produce a fixed-size digest from arbitrary input, so they cannot be inverted to recover the original data. This core property immediately helps evaluate the statements.

1) Relevant knowledge points and concepts
- One-way / preimage resistance: given hash(x) it is computationally infeasible to find x.
- Determinism: same input yields same hash, enabling comparisons.
- Use in password storage: systems store password hashes (usually salted and iterated) rather than plaintext.
- Integrity checking: comparing hashes detects accidental or malicious changes to data.
- Reversibility is a property of encryption, not hashing; keyed constructions (HMAC) authenticate integrity but are not reversible to recover the input.

2) Step-by-step reasoning applied to each statement
- i. "It is a one-way function" — True. Hash functions are intended to be one-way (preimage resistance).
- ii. "Used for password storage" — True. Best practice is to store salted, slow hashes of passwords so the plaintext password is not stored.
- iii. "Can be reversed with the correct key" — False. Hashing is not reversible even with a “key.” Keyed hashes (e.g., HMAC) use a key for authentication but do not allow recovering the original input; reversing would be encryption, not hashing.
- iv. "Ensures data integrity" — True in practice: if two hashes differ, the data differs. Hashes provide a practical integrity check (subject to collision risk, which strong hashes make extremely unlikely).

3) Intermediate/illustrative example (no arithmetic): password "P@ssw0rd" -> hash H = SHA-256("P@ssw0rd" + salt). You cannot compute "P@ssw0rd" back from H; you can only verify by hashing a candidate and comparing.

4) Why the correct answer is correct
Because statements i, ii and iv accurately describe hashing, while iii confuses hashing with reversible encryption.

5) Why other options are incorrect
- B (ii and iii only): includes iii, which is wrong.
- C (All of the above): includes iii, so incorrect.
- D (i and ii only): omits iv, which is a valid property (hashes are used for integrity checks).

Conclusion: The correct choice is A (i, ii, and iv only), matching the provided answer.

Which statements about hashing are correct? i. It is a one-way functionii. Used for password storageiii. Can be reversed with the correct keyiv. Ensures data integrity单项选择题

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