Merkle Root of Bitcoin Block

Bitcoin Tutorials - Herong's Tutorial Notes

∟Merkle Root of Bitcoin Block

This section describes the Merkle Root of a Bitcoin Block.

The Merkle Root of A Bitcoin block is the hash of all transaction hashes.

For example, block # 500 of the Bitcoin Test Network has the following Merkle Root and transaction hashes:

  ...
  "height": 500,
  "merkleroot": 
     "dd3f288510dd3b632940bd3fb1db162d3ff99b19ddb0c586cfa3ac9a76d42517",
  "tx": [
    "a647d0c4112b4727f3c856782ff6bbaf099be929b27214a8e0dfedee4383eb68", 
    "24b8a4c788b8c805b810438ddd99e569e184ff20f4394ac49a6d832e69f57242", 
    "c5ffd70c3bc4998465cef55ed6d5d831ab3a550406423eb611117ed8ee41c278", 
    "4692772a73ea834c836915089acf97f2c790380a2b8fd32f82729da72545d8c5", 
    "82d6d88081e3e0eb36730f7f3aedb17228142b9e00a6dbaab4b53b798d0742c1", 
    "fc407d7a3b819daa5cf1ecc2c2a4b103c3782104d1425d170993bd534779a0da", 
    "95ad3ffb2a9426d6f5f5b97a134d90153ae16c9375f74eb385f481cff2771d77"
  ],
  ...

Here is the algorithm of how to calculate the Merkle Root:

1. Get the SHA256 hash of each transactions: H1, H2, H3, ..., Hn = tx1, tx2, tx3, ..., txn.
2. Convert transaction hash values in little-endian hex notation, if they are displayed in big-endian hex notation as with most Bitcoin tools including Bitcoin Core and blockchain.com.
3. Group the hash list into groups of 2 sequentially. Clone the last hash, if the list has an odd number of hashes: (H1, H2), (H3, H4), ...
4. Generate a new hash for each group by running SHA256() function twice: H1 = SHA256(SHA256(H1+H2)), H2 = SHA256(SHA256(H3+H4)), ...
5. Repeat Step 3 and 4 on the new hash list, until the list has only 1 last hash: H1.
6. Return the last hash as the Merkle Root: merkleroot = H1
7. Convert the Merkle Root in big-endian hex notation, in order to compare it with other Bitcoin tools.