Solution.md added

Solution.md

@@ -0,0 +1,103 @@
+# Block Construction Program Documentation
+
+## Design Approach
+
+The block construction program simulates the process of constructing a valid block in a blockchain system. It involves several key steps and concepts:
+
+### 1. Transaction Validation
+
+Transactions are validated to ensure they meet specified criteria:
+
+- **Structure Check**: Validate the presence of required fields (`vin`, `vout`) in each transaction.
+- **Size Limitation**: Ensure transactions do not exceed a predefined maximum size (`MAX_BLOCK_SIZE_BYTES`) to prevent oversized blocks.
+- **Script Validation**: Perform specific validations based on `scriptpubkey_type` to enforce transaction rules (e.g., `p2pkh`, `p2wsh`).
+
+### 2. Transaction Selection
+
+Selected transactions are included in the block based on their weight:
+
+- **Weight Calculation**: Compute the weight of each transaction considering base size and witness data (if present).
+- **Weight Sorting**: Sort transactions by weight and select a subset that collectively do not exceed a specified `max_total_weight`.
+
+### 3. Merkle Root Calculation
+
+The Merkle root hash summarizes included transactions for integrity:
+
+- **Transaction Serialization**: Serialize transaction IDs of selected transactions.
+- **Merkle Tree Construction**: Build a Merkle tree using a pairwise hashing function (`hash2`) to compute the Merkle root hash.
+
+### 4. Block Mining
+
+Simulates the mining process to find a valid block hash meeting the `difficulty_target`:
+
+- **Nonce Iteration**: Adjust the `nonce` in the block header iteratively to find a hash satisfying the difficulty target.
+- **Block Header Assembly**: Construct the block header with version, previous block hash, Merkle root, timestamp, bits, and nonce.
+- **Hash Computation**: Compute the double SHA-256 hash of the block header and validate against the difficulty target.
+
+## Implementation Details
+
+### Transaction Validation
+
+The `validate_transaction` function checks transactions for validity:
+
+- Ensures necessary fields (`vin`, `vout`) are present.
+- Validates transaction size and enforces script-specific rules (`p2pkh`, `p2wsh`).
+
+### Transaction Selection
+
+The `trim_transactions` function filters and selects transactions by weight:
+
+- Calculates and sorts transactions by weight.
+- Selects a subset of transactions to meet the `max_total_weight` constraint.
+
+### Merkle Root Calculation
+
+The `merkle_root` function computes the Merkle root hash of included transactions:
+
+- Serializes transaction IDs and constructs a Merkle tree using a recursive pairwise hashing technique (`hash2`).
+- Returns the root of the Merkle tree for transaction integrity.
+
+### Block Mining
+
+The `mine_block` function simulates block mining to find a valid block hash:
+
+- Iteratively adjusts the `nonce` in the block header to meet the `difficulty_target`.
+- Constructs the block header and computes the block hash using double SHA-256 hashing.
+
+## Results and Performance
+
+The block construction program successfully constructs a valid block based on selected transactions:
+
+- Efficiently filters and selects transactions to optimize block size and weight.
+- Computes the Merkle root hash to ensure transaction integrity.
+- Simulates the block mining process to find a valid block hash within the defined difficulty target.
+
+### Performance Analysis
+
+- **Validation Efficiency**: Transaction validation and selection are optimized for handling a large number of transactions.
+- **Merkle Root Computation**: The Merkle root calculation is performed efficiently using recursive hashing.
+- **Block Mining Optimization**: The block mining process iteratively adjusts the `nonce` to find a valid block hash meeting the difficulty target.
+
+## Conclusion
+
+In conclusion, the block construction program demonstrates core blockchain concepts:
+
+- Transaction validation and selection based on weight and size.
+- Merkle tree construction for summarizing and securing transactions.
+- Block mining to secure the blockchain and maintain consensus.
+
+## Future Improvements
+
+Potential areas for future enhancement and research include:
+
+- Mining algorithm optimization for faster block discovery.
+- Enhanced validation rules and script execution for improved transaction security.
+- Integration with a larger blockchain network to test scalability and interoperability.
+
+## References
+
+- Bitcoin Whitepaper: Satoshi Nakamoto (2008)
+- Python Standard Library Documentation: hashlib, json
+- ECDSA Documentation: Cryptographic Operations
+- Learn me bitcoin: [https://learnmeabitcoin.com/](https://learnmeabitcoin.com/)
+- Ken Shirriff's blog: [Ken Shirriff's blog](https://www.righto.com/2014/02/bitcoins-hard-way-using-raw-bitcoin.html)