Which of the following statements correctly describe properties or applications of hash functions?

Question

BlackTom AI · Accepted Answer

Collision resistance means it is hard to find two different inputs that produce the same hash output (a collision). Hash functions used in cryptography are designed to make finding such pairs computationally infeasible.

1. Relevant knowledge points and concepts
- Hash function: a deterministic function that maps arbitrary-length input to fixed-size output (digest).
- Determinism: same input -> same output every time.
- One-way (preimage resistance): given a hash, it should be computationally infeasible to recover the original input.
- Collision resistance: it should be computationally infeasible to find any two distinct inputs that hash to the same digest.
- Salt: a random value combined with a password before hashing to ensure identical passwords hashed with different salts yield different digests.

2. Step-by-step reasoning
Step 1: Evaluate "Collision resistance means it is hard to find two different inputs with the same hash." By definition of collision resistance in cryptographic hashing, this statement is correct: it describes exactly what collision resistance means.  
Step 2: Evaluate "Adding salt prevents identical passwords from producing the same hash." Salt is concatenated or otherwise combined with a password before hashing; if two users use the same password but different salts, the resulting hashes differ. Therefore this statement is correct (note: salt does not make a password secure by itself but prevents identical hashes across different salt values).  
Step 3: Evaluate "Hash functions are reversible, allowing recovery of the original input." This contradicts the one-way property; cryptographic hashes are not reversible, so this statement is false.  
Step 4: Evaluate "Hash functions always produce different outputs for the same input." Determinism implies the opposite: the same input always yields the same output for a given hash algorithm and parameters, so this statement is false.

3. Intermediate logical steps
- Deterministic property => identical input -> identical output (contradicts the fourth option).  
- One-way property => cannot recover input from hash (contradicts the third option).  
- Salt application => hash(password, salt1) ≠ hash(password, salt2) when salts differ, so identical passwords across different salts do not produce the same hash.

4. Why the correct answers are correct
The first option restates the formal definition of collision resistance. The second option correctly describes the practical role of salts in password hashing: to ensure identical passwords do not yield identical stored hashes across different salts.

5. Why other options are incorrect
- Reversible: false because cryptographic hashes are designed to be one-way.  
- Always different outputs for same input: false because hash functions are deterministic; same input gives same digest.

6. Conclusion
The correct choices are "Collision resistance means it is hard to find two different inputs with the same hash" and "Adding salt prevents identical passwords from producing the same hash," which matches the provided answers.

Which of the following statements correctly describe properties or applications of hash functions?多项选择题

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