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SESK: Stuff Everyone Should Know · sesk.info/secplus-blockchain-previous-hash

What cryptographically links each block in a blockchain to the one before it?

The previous block's hash, stored in each new block.

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  1. The previous block header's hash ✔
  2. The miner's password
  3. A shared symmetric session key

Why: Each block header includes a hash of the previous block. Change an old block and its hash changes, which breaks every link after it, so tampering is easy to spot.

Huh, didn't know that: NIST IR 8202 says blockchains are tamper evident and tamper resistant, but not strictly immutable.

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Why was the blockchain so well organized? Every block knew exactly who came before it.
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References

Answer: The previous block header's hash. Each block header includes a hash of the previous block. Change an old block and its hash changes, which breaks every link after it, so tampering is easy to spot.

  1. NIST IR 8202, Blockchain Technology Overview nvlpubs.nist.gov/nistpubs/ir/2018/NIST.IR.8202.pdf
    Every block header (except for the very first block of the blockchain) contains a cryptographic link to the previous block’s header.
    Checked 2026-10-10.
  2. NIST IR 8202, Blockchain Technology Overview nvlpubs.nist.gov/nistpubs/ir/2018/NIST.IR.8202.pdf
    They are tamper evident and tamper resistant
    Checked 2026-10-10.

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