Question at position 5 Changing even one character in the input of a secure hash function will...Swap one segment onlyProduce a very different hash Keep the hash similarRaise an exceptionClear my selection单项选择题
A
Swap one segment only
B
Produce a very different hash
C
Keep the hash similar
D
Raise an exception

Question

Question at position 5 Changing even one character in the input of a secure hash function will...Swap one segment onlyProduce a very different hash Keep the hash similarRaise an exceptionClear my selection单项选择题

A

Swap one segment only

B

Produce a very different hash

C

Keep the hash similar

D

Raise an exception

BlackTom AI · Accepted Answer

A secure cryptographic hash function exhibits the avalanche effect: a tiny change in the input should produce a completely different output (hash). This underlies the correct choice "Produce a very different hash."

1) Relevant knowledge points and concepts
- Cryptographic hash functions map arbitrary-length input to fixed-length outputs deterministically.
- Key security properties: preimage resistance, second-preimage resistance, collision resistance, and diffusion/avalanche.
- Avalanche effect: flipping a single input bit should change each output bit with ~50% probability, so the outputs look uncorrelated.

2) Step-by-step reasoning
- Start with two inputs that differ by a single character (which changes several input bits).
- The hash algorithm processes input in blocks through nonlinear compression, mixing, bitwise ops, and permutations.
- Each round mixes input bits into internal state; due to nonlinearity, the single input change propagates and rapidly affects many internal bits.
- After full processing, the final output bits are essentially uncorrelated with the original output bits, producing a very different hash.

3) Intermediate calculation / quantitative illustration
- For a 256-bit hash (e.g., SHA-256) the avalanche expectation is ~50% of bits flipped. That means roughly 256 × 0.5 = 128 bits will differ between the two hashes. This is a simple numeric illustration of “very different.”

4) Why the correct answer is correct
- The avalanche property is deliberately designed so that small input differences yield large, unpredictable output differences. That makes “Produce a very different hash” the expected outcome when changing one character.

5) Why the other options are incorrect
- "Swap one segment only": Misleading — hash outputs are not segmented in a way that maps to one-to-one input segments; they do not swap only one segment.
- "Keep the hash similar": Contradicts the avalanche requirement; a secure hash should not produce similar hashes for similar inputs.
- "Raise an exception": Hash functions accept arbitrary-length input; they don’t raise exceptions simply because an input changed by one character.

6) Conclusion
The correct answer is "Produce a very different hash," which matches the provided answer.

Question at position 5 Changing even one character in the input of a secure hash function will...Swap one segment onlyProduce a very different hash Keep the hash similarRaise an exceptionClear my selection单项选择题

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