Blockchain Basics

2. Cryptographic Foundations

Understand the security primitives:

• Hash Functions: SHA-256, Keccak-256, properties
• Digital Signatures: ECDSA, Ed25519, verification
• Merkle Trees: Proof construction, verification

3. Network Architecture

Explore distributed systems:

• P2P Networks: Gossip protocols, peer discovery
• Node Types: Full nodes, light clients, archives
• Block Propagation: Compact blocks, relay networks

4. Transaction Lifecycle

Follow data through the chain:

• Transaction Structure: Inputs, outputs, signatures
• Mempool: Fee markets, ordering, priority
• Confirmation: Finality, reorganization

Code Examples

Verify Merkle Proof

import hashlib

def verify_merkle_proof(leaf: bytes, proof: list, root: bytes) -> bool:
    """Verify a Merkle proof for inclusion"""
    current = leaf
    for sibling, is_left in proof:
        if is_left:
            current = hashlib.sha256(sibling + current).digest()
        else:
            current = hashlib.sha256(current + sibling).digest()
    return current == root

Calculate Block Hash

import hashlib
import struct

def calculate_block_hash(header: dict) -> bytes:
    """Calculate Bitcoin-style block hash"""
    data = struct.pack(
        '<I32s32sIII',
        header['version'],
        bytes.fromhex(header['prev_block']),
        bytes.fromhex(header['merkle_root']),
        header['timestamp'],
        header['bits'],
        header['nonce']
    )
    return hashlib.sha256(hashlib.sha256(data).digest()).digest()[::-1]

Common Pitfalls

Troubleshooting

"Why is my transaction not confirming?"

1. Check transaction fee vs current mempool
2. Verify nonce is sequential (no gaps)
3. Ensure sufficient balance for amount + gas

"How do I verify a signature?"

from eth_account import Account
from eth_account.messages import encode_defunct

message = encode_defunct(text="Hello")
address = Account.recover_message(message, signature=sig)

Learning Path

[Beginner] → Hash Functions → Digital Signatures → Transactions
    ↓
[Intermediate] → Merkle Trees → Consensus → Network Layer
    ↓
[Advanced] → BFT Protocols → Sharding → Cross-chain

Test Yourself

# Unit test template
def test_merkle_root():
    txs = [b"tx1", b"tx2", b"tx3", b"tx4"]
    root = build_merkle_root(txs)
    assert len(root) == 32
    assert verify_merkle_proof(txs[0], get_proof(0), root)

Cross-References

• Bonded Agent: 01-blockchain-fundamentals
• Related Skills: ethereum-development, smart-contract-security

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