# BSV Blocks and SHA-256
#### What is a BSV Block?
A **BSV block** is a **time-stamped package** containing all transactions accumulated between two **proof-of-work solutions**.
* Like TXIDs, **Block IDs** are generated by applying **double SHA-256 (HASH-256)** to the serialized block header.
* The system adjusts difficulty to ensure a new block is discovered roughly **every 10 minutes**.
Each block contains:
* **All validated transactions** collected by the winning node.
* Any **data payloads** attached to those transactions.
* A **block header**, which includes:
* **Version field** (4 bytes, little endian)
* **Previous block hash** (32 bytes, little endian)
* **Merkle Root Hash** (32 bytes, little endian)
* **Time field** (4 bytes, big endian, Unix epoch)
* **nBits** (4 bytes, little endian, defines current difficulty target)
* **Nonce** (4 bytes, little endian, value miners adjust to find proof-of-work solution)
***
#### Example Block (Deserialized JSON)
```
{
"tx": [
"63fde109a6f22a611fe80847eb43f34b1cef0ec095273c3cbf12b0164295796b",
"d94f1db2079b1a3f4c4936e0f47434e09ab7eef7a1d35d2fc6af5dd9e87b4f84"
],
"hash": "0be14bde7beb17c481b5bc78496ef129c25e16401d78419e789f9629db6057e4",
"confirmations": 155,
"size": 406,
"height": 284,
"version": 536870912,
"versionHex": "20000000",
"merkleroot": "f15b44eebcf7a3c3009cc6acd3bd1dd74f256448936c88ad72f39b55981ddffd",
"num_tx": 2,
"time": 1647415283,
"mediantime": 1647412906,
"nonce": 0,
"bits": "207fffff",
"difficulty": "4.656542373906925e-10",
"chainwork": "000000000000000000000000000000000000000000000000000000000000023a",
"previousblockhash": "74f52bbca1a9a4f7f13f85cdcd24c7f49650cd1d463421373eb3bcb683868712",
"nextblockhash": "7e976012ba0a1cd9eeba8fb57ba41c982b914cffcd17fe46b84c0a0333db79eb",
"coinbaseTx": {
"txid": "63fde109a6f22a611fe80847eb43f34b1cef0ec095273c3cbf12b0164295796b",
"hash": "63fde109a6f22a611fe80847eb43f34b1cef0ec095273c3cbf12b0164295796b",
"version": 2,
"size": 100,
"locktime": 0,
"vin": [
{
"coinbase": "021c010101",
"sequence": 4294967295
}
],
"vout": [
{
"value": 25.00000113,
"n": 0,
"scriptPubKey": {
"asm": "03642fd43b260aab1f0241535c9fabec5445bdc42591a5be9d555a6e33c96a09d8 OP_CHECKSIG",
"hex": "2103642fd43b260aab1f0241535c9fabec5445bdc42591a5be9d555a6e33c96a09d8ac",
"reqSigs": 1,
"type": "pubkey",
"addresses": [
"mjvmz3xW4nTbjtKsmbfhsXB9gtm9GBddJg"
]
}
}
],
"blockhash": "0be14bde7beb17c481b5bc78496ef129c25e16401d78419e789f9629db6057e4",
"confirmations": 155,
"time": 1647415283,
"blocktime": 1647415283,
"blockheight": 284,
"hex": "02000000010000000000000000000000000000000000000000000000000000000000000000ffffffff05021c010101ffffffff0171f9029500000000232103642fd43b260aab1f0241535c9fabec5445bdc42591a5be9d555a6e33c96a09d8ac00000000"
},
"totalFees": "-24.99999887",
"miner": "\u0002\u001c\u0001\u0001\u0001",
"txCount": 2
```
The below table breaks down the block header for the above block:
👉 **Key takeaway:** The **block header** ties the block to its predecessor, ensures data integrity via the **Merkle Root**, and encodes the difficulty/nonce for proof-of-work.
#### UTXO Sets and Mempools
* All **unspent outputs (UTXOs)** are tracked in a node’s **UTXO set**.
* **New transactions** are validated and held temporarily in the node’s **mempool**.
* A **Merkle Tree** is constructed from these transactions, with the root placed into the **block header**.
* Once a UTXO is consumed as an input, it is **removed** (often pruned) from the UTXO set.
***
#### How is a BSV Block Created?
1. **Transactions are broadcast** to the network.
2. Nodes validate transactions against **consensus rules** and **local policies**.
3. Valid transactions are added to the **Merkle Tree**.
4. Nodes create **block header templates** and send them to miners.
5. Miners iterate through **nonce values**, hashing headers with SHA-256 twice, searching for a valid **proof-of-work solution**.
6. When a valid solution is found:
* A **new block ID** is finalized.
* The block is **broadcast** to the network.
* Other nodes **accept the block** by building on top of it.
7. After **99 additional blocks** confirm it, the block’s **coinbase reward** becomes **spendable**.
***
✅ **Summary:** BSV blocks are **containers of transactions**, secured with **double SHA-256**, and validated through **proof-of-work**. Each block links back to the previous one, forming a tamper-proof, time-stamped chain of records.
---
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