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CS Professional · Artificial Intelligence, Data Analytics and Cyber Security - Laws and Practice · Internet and Other Technologies

A firm stores a ledger of transactions in which each block holds a cryptographic hash of the previous block, and the record is replicated across many participants. Why is it hard to alter an old entry unnoticed?

Because each block contains the hash of the previous one, altering an old entry changes its hash and breaks every later link. As the ledger is replicated among many participants, the tampered copy would also fail to match the others, so tampering is easily detected.

  1. AChanging one block alters its hash and breaks the links in all later blocks, and the other copies would not matchCorrect
  2. BEvery block is stored in a separate paper register kept by a regulator
  3. CThe hash of each block is deleted after creation, so no checks are possible
  4. DOnly one participant holds the ledger and keeps a private password

Explanation

In a blockchain each block includes the previous block's hash, so editing an old block changes its hash and invalidates the chain that follows. Because the ledger is replicated among participants, the altered copy would also disagree with the others. The remaining options describe features that blockchains do not have.

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