Question at position 14 Which cryptographic method is used to secure the integrity of blocks in a blockchain? (Choose the best answer.) Digital signaturesSymmetric encryptionHashingPublic-key encryption单项选择题
A
Digital signatures
B
Symmetric encryption
C
Hashing
D
Public-key encryption

Question

Question at position 14 Which cryptographic method is used to secure the integrity of blocks in a blockchain? (Choose the best answer.) Digital signaturesSymmetric encryptionHashingPublic-key encryption单项选择题

A

Digital signatures

B

Symmetric encryption

C

Hashing

D

Public-key encryption

BlackTom AI · Accepted Answer

Hash functions produce a fixed-size digest uniquely (for practical purposes) tied to input data, so they are the core mechanism that secures block integrity in a blockchain.

1. Relevant knowledge points and concepts
- Hashing: deterministic function mapping arbitrary data to a fixed-size hash; properties include pre-image resistance, second pre-image resistance, and collision resistance (practical tamper-evidence).
- Blockchain structure: each block stores a payload, a block header, and the hash of the previous block (and often a Merkle root of transactions). This creates a chain of dependent hashes.
- Other cryptographic primitives: digital signatures (authenticity/authorization), symmetric/public-key encryption (confidentiality), which serve different purposes.

2. Step-by-step reasoning process
- A block Bn contains data Dn and the previous block’s header hash H(Bn-1).
- Compute H(Bn) = Hash(headerBn || Dn). The network validates that H(Bn) was computed correctly and that H(Bn) matches the stored value.
- If an attacker modifies Dn-1, then H(Bn-1) changes. Because Bn stores the old H(Bn-1), the chain validation fails.
- Therefore, tampering with any past block requires recomputing all subsequent block hashes (and meeting proof-of-work or consensus constraints), making tampering detectable and expensive.

3. Intermediate steps (illustrative)
- Suppose Hash("Block1 data") = h1 = 0xAA.
- Block2 stores prevHash = h1 and its data; Hash("prev=0xAA||Block2 data") = h2 = 0xBB.
- Change Block1 data → new h1' = 0xCC. Block2 still has prevHash=0xAA but recomputed prev is 0xCC → mismatch. Chain invalid.

4. Why hashing is correct
- Hash properties make any modification to a block change its hash, instantly breaking links to subsequent blocks. The blockchain’s integrity depends on this tamper-evident chaining of hashes.

5. Why other options are incorrect
- Digital signatures: ensure origin/authenticity of transactions or blocks (who created them), not the fundamental linking/tamper-evidence mechanism between blocks.
- Symmetric encryption: provides confidentiality when encrypting data but does not provide tamper-evident chaining.
- Public-key encryption: also mainly for confidentiality or key exchange; public-key cryptography underlies digital signatures but is not what links blocks for integrity.

6. Conclusion
Hashing is the correct answer and matches the provided answer: Hashing.

Question at position 14 Which cryptographic method is used to secure the integrity of blocks in a blockchain? (Choose the best answer.) Digital signaturesSymmetric encryptionHashingPublic-key encryption单项选择题

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