blockchain.mit.edu Courses

Live Blockchain Demo

4. Blockchain

A blockchain links blocks together: each block includes the previous block's hash. Change the data in block 2 and blocks 2–5 all break — that's what makes a blockchain tamper-evident. The further back a change is, the more work it takes to re-mine the chain after it.

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0000000000000000000000000000000000000000000000000000000000000000 000015783b764259d382017d91a36d206d0600e2cbb3567748f46a33fe9297cf
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000015783b764259d382017d91a36d206d0600e2cbb3567748f46a33fe9297cf 000012fa9b916eb9078f8d98a7864e697ae83ed54f5146bd84452cdafd043c19
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000012fa9b916eb9078f8d98a7864e697ae83ed54f5146bd84452cdafd043c19 0000b9015ce2a08b61216ba5a0778545bf4ddd7ceb7bbd85dd8062b29a9140bf
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0000b9015ce2a08b61216ba5a0778545bf4ddd7ceb7bbd85dd8062b29a9140bf 0000ae8bbc96cf89c68be6e10a865cc47c6c48a9ebec3c6cad729646cefaef83
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0000ae8bbc96cf89c68be6e10a865cc47c6c48a9ebec3c6cad729646cefaef83 0000e4b9052fd8aae92a8afda42e2ea0f17972ea67cead67352e74dd6f7d217c

Next: 5. Distributed Blockchain →

This interactive demo was created by Anders Brownworth and is rebuilt here as a self-hosted, dependency-free version. SHA-256 runs entirely in your browser; blocks turn red when their hash no longer starts with 0000 and green again once re-mined.