Understanding Difficulty and Forks
In Proof of Work (PoW), miners compete to find a block hash that meets the difficulty target by adjusting a nonce. The difficulty determines how many leading zeros the hash must have. Forks occur when multiple miners solve a block simultaneously, creating competing chains.
Blockchain Simulation
| Field | Value |
|---|---|
| Block Number | 1001 |
| Hash Algorithm |
|
| Difficulty (Leading Zeros) |
|
| Block Hash |
Fork Competition
| Block Number | Miner 1 | Miner 2 | Miner 3 |
|---|
Simplified vs. Bitcoin Difficulty
This simulation uses a simple way to measure difficulty, but Bitcoin’s method is more complex. Here’s how they differ, explained for students:
Simplified Difficulty (This Simulation)
In this simulation, difficulty means how many zeros must appear at the start of a hash. For example, if difficulty is 4, the hash must start with “0000”. Miners try different nonces (numbers) until they find a hash with enough leading zeros.
Example: Suppose we hash “1002 + Merkle Root + Previous Block + Nonce” with MD5. We want 4 leading zeros (difficulty 4). After trying nonces, we find:
Hash: 0000a1b2c3d4e5f67890123456789abc
Result: Success! The hash starts with “0000”.
This is like guessing a code that starts with four zeros—easy to understand but not exactly how Bitcoin works.
Bitcoin’s Difficulty
Bitcoin uses a “target” number. The hash of a block header must be less than or equal to this target. A smaller target means higher difficulty, and small targets produce hashes with many leading zeros. Bitcoin adjusts the target every 2016 blocks (about 2 weeks) to keep blocks coming every 10 minutes.
Example: Imagine Bitcoin’s target is a small number, like 0000000000000000001f (in hex, a 256-bit number - so the actual full target is: 0000000000000000001f00000000000000000000000000000000000000000000). The miner hashes the block header (version, previous block, Merkle root, timestamp, bits, nonce) with double SHA256. After trying nonces, they find:
Hash: 0000000000000000000a1b2c3d4e5f...
Result: Success! The hash is less than the target (0000000000000000001f...).
This is like a game where you roll a huge dice (256 bits) and need a number smaller than a tiny target. The smaller the target, the more leading zeros the hash tends to have.
Key Differences
- Metric: Simulation uses leading zeros (e.g., 4 zeros). Bitcoin uses a numerical target (hash must be below it).
- Adjustment: Simulation’s difficulty is fixed or manual. Bitcoin adjusts difficulty automatically every 2016 blocks.
- Input: Simulation hashes a simple string (Block Number + Merkle Root + Previous Block + Nonce). Bitcoin hashes a full block header with more fields.
- Hash Function: Simulation uses single MD5 or SHA256. Bitcoin uses double SHA256 (SHA256(SHA256(header))).
The simulation makes difficulty easy to visualize with leading zeros, while Bitcoin’s target system is more precise and flexible for a real-world network.
Acknowledgments
Special thanks to Grok, for its invaluable assistance in creating this PoW topic for Deep Inside workshop series.