Blockchain Technology Deep Dive: Understanding the Underlying Logic of Cryptocurrency

Quick Overview: This article provides an accessible introduction to blockchain technology principles, offering a complete knowledge framework for understanding cryptocurrency's underlying technology. Estimated reading time: 16 minutes.

What is Blockchain?

Blockchain is a distributed ledger technology that uses cryptographic methods to link data blocks into a chain, achieving a decentralized trust mechanism. It is the underlying technology of Bitcoin and the infrastructure of Web3.

Core Characteristics of Blockchain

History of Blockchain

How Blockchain Works

Block Structure

Block = Block Header + Transaction List

Block Header:
├── Previous Block Hash
├── Timestamp
├── Merkle Root (transaction summary)
├── Nonce (Proof of Work)
├── Difficulty Target
└── Version

Transaction List:
├── Transaction 1 (input, output, signature)
├── Transaction 2
├── ...
└── Transaction N

Block Size:
├── Bitcoin: about 1-2 MB
├── Ethereum: dynamically adjusted
└── Each block contains hundreds to thousands of transactions

Chain Structure

Blockchain Connection:

Block 1 [Hash: 0000a...]
    ↓
Block 2 [Hash: 0000b...] ← Contains Block 1's hash
    ↓
Block 3 [Hash: 0000c...] ← Contains Block 2's hash
    ↓
Block 4 [Hash: 0000d...] ← Contains Block 3's hash

Security Features:
├── Modify Block 2's data → Block 2's hash changes
├── Block 3's previous hash doesn't match → chain breaks
├── Need to recalculate all subsequent blocks
└── Almost impossible in a distributed network

Cryptography Fundamentals

Hash Functions

Hash functions are the digital fingerprint technology of blockchain.

#### Hash Function Characteristics

Input: Any data ("Hello World")
    ↓
Hash Function (SHA-256)
    ↓
Output: Fixed-length hash value
(a591a6d40bf420404a011733cfb7b190d62c65bf0bcda32b57b277d9ad9f146e)

Key Characteristics:
├── Deterministic: Same input → Same output
├── Sensitivity: Small change → Completely different output
├── Irreversible: Cannot reverse from output to input
├── Collision-resistant: Extremely difficult to find two inputs with same output
└── Fast computation: Can be quickly verified

#### SHA-256 Example

import hashlib

# Original data
data = "Hello, Blockchain!"

# Calculate SHA-256 hash
hash_object = hashlib.sha256(data.encode())
hash_hex = hash_object.hexdigest()

print(f"Input: {data}")
print(f"SHA-256: {hash_hex}")
# Output: 7f83b1657ff1fc53b92dc18148a1d65dfc2d4b1fa3d677284addd200126d9069

# Small change
data2 = "Hello, Blockchain?"  # Exclamation to question mark
hash2 = hashlib.sha256(data2.encode()).hexdigest()

print(f"New hash: {hash2}")
# Completely different output: a3f5c8e1d2b4... (completely different)

Asymmetric Encryption

Key Pair:
├── Public Key: Shared publicly, used for verification
├── Private Key: Kept secret, used for signing
└── Relationship: Private key can derive public key, but not vice versa

Applications:
├── Digital Signature: Private key signs, public key verifies
├── Encrypted Communication: Public key encrypts, private key decrypts
└── Identity Proof: Prove ownership of private key without revealing it

Digital Signatures

Transaction Signing Process:

1. Create Transaction:
   "Alice sends 1 BTC to Bob"

2. Calculate Transaction Hash:
   hash = SHA256(transaction data)

3. Private Key Signature:
   signature = sign(hash, Alice's private key)

4. Broadcast Transaction:
   Transaction data + Signature + Alice's public key

5. Verification:
   verify(signature, hash, Alice's public key) = True/False

Security:
├── Only private key holder can produce valid signature
├── Anyone can verify with public key
├── Signatures cannot be forged
└── Signature is bound to specific transaction

Consensus Mechanisms

Consensus mechanisms are the rules for reaching agreement in blockchain, solving the "Byzantine Generals Problem" in distributed systems.

Proof of Work (PoW)

#### Principle

Mining Process:
├── Miners collect pending transactions
├── Form candidate block
├── Find Nonce such that block hash < target value
├── First to find broadcasts to the network
├── Broadcast new block, other nodes verify
└── Verification passed, block joins the chain

Difficulty Adjustment:
├── Adjusted every 2016 blocks (Bitcoin about 2 weeks)
├── Goal: Maintain average of one block every 10 minutes
├── Increased hash power → Increased difficulty
└── Decreased hash power → Decreased difficulty

#### Security Analysis

51% Attack:
├── Attacker controls more than 50% of hash power
├── Can:
│   ├── Prevent transaction confirmations
│   ├── Reverse own transactions (double-spend)
│   └── Affect block generation speed
├── Cannot:
│   ├── Modify others' transactions
│   ├── Create Bitcoin out of thin air
│   └── Completely stop the network
└── Economically irrational: Attack cost > benefit

Reality:
├── Bitcoin's global hash power is extremely large
├── Attack cost in billions of dollars
├── Successful attack would destroy Bitcoin's value
└── Rational miners won't attack

Proof of Stake (PoS)

#### Principle

Validator Selection:
├── Selected based on coin holdings and time held
├── More coins held, longer time, higher probability of selection
├── Selected validator responsible for generating and validating blocks
└── Malicious actors are slashed (forfeiting staked coins)

Pros:
├── Energy efficient (no massive computation needed)
├── Fast (second-level confirmation)
├── Decentralized (lower hardware barrier)
└── Economic security (high cost of malicious activity)

Cons:
├── Rich get richer (need to hold coins)
├── No historical cost (can attack long-term)
├── Higher complexity
└── Relatively new, not long-term tested

Other Consensus Mechanisms

The Meaning of Decentralization

Why Decentralize?

Centralization Problems:
├── Single point of failure (banking system crashes)
├── Censorship risk (accounts frozen)
├── Privacy leaks (data stolen)
├── Inflation risk (currency over-issuance)
└── Intermediary costs (fees, time)

Decentralization Solutions:
├── Distributed redundancy (no single point of failure)
├── Censorship-resistant (cannot stop transactions)
├── Self-custody (keep your own assets)
├── Fixed rules (cannot over-issue)
└── Peer-to-peer (reduce intermediary costs)

The Cost of Decentralization

FAQ - Frequently Asked Questions

Q1: Are blockchain and Bitcoin the same thing?

A: No:

• Blockchain is the technology
• Bitcoin is an application
• Bitcoin uses blockchain technology
• Blockchain has other applications

Q2: Can blockchain only be used for cryptocurrency?

A: No, it can also be used for:

• Supply chain tracking (food, pharmaceuticals)
• Identity verification (academic credentials, licenses)
• Voting systems (transparent, fraud-resistant)
• Medical records (privacy, sharing)
• Smart contracts (automatic execution)

Q3: Why is blockchain immutable?

A: Reasons:

1. Cryptographic connection: Modifying data changes the hash
2. Distributed storage: Thousands of nodes hold copies
3. Consensus mechanism: Requires majority agreement to modify
4. Economic cost: Attack cost is extremely high

Q4: What do miners do?

A: Miner responsibilities:

• Package transactions into blocks
• Compete for accounting rights (PoW) or validate blocks (PoS)
• Maintain network security
• Receive block rewards

Q5: Why is blockchain slow?

A: Reasons:

• Decentralization requires consensus: Multiple nodes confirm
• Security and speed trade-off: Slower = Safer
• Bitcoin: about 7 transactions/second
• Ethereum: about 15 transactions/second
• Solutions: Layer 2, sharding

Q6: What are smart contracts?

A: Automatically executing code:

• Deployed on blockchain
• Automatically execute when conditions are met
• No intermediaries needed
• Ethereum pioneered and popularized

Q7: Future development of blockchain?

A: Trends:

• Cross-chain interoperability: Different blockchains communicate
• Layer 2 scaling: Increased throughput
• Enterprise applications: Supply chain, finance
• Regulatory compliance: Integration with traditional finance
• Privacy protection: Zero-knowledge proof and other technologies

Q8: How to learn blockchain technology?

A: Learning path:

1. Understand basic concepts (this article)
2. Learn cryptography fundamentals
3. Read Bitcoin whitepaper
4. Practice with actual cryptocurrency operations
5. Learn smart contract development (Solidity)
6. Participate in open-source projects

Related Articles

Same Series Extended Reading

• Bitcoin Beginner's Guide - The first blockchain application
• Ethereum and Smart Contracts - Programmable blockchain
• Cryptocurrency Wallet Guide - Secure storage details

Cross-Series Recommendations

• DeFi Beginner's Guide - Decentralized finance applications
• Smart Contract Security - Protect your assets
• Cryptocurrency Mining - Participate in blockchain consensus

Conclusion: The Machine of Trust

The core value of blockchain lies in establishing trust without trusting third parties. This is achieved through:

• Cryptography for security
• Consensus mechanisms for consistency
• Decentralization for censorship resistance

Understanding blockchain means understanding the new trust mechanism of the digital age.

Further Reading:

• Bitcoin Whitepaper
• "Blockchain Revolution"
• "Mastering Bitcoin"

Author: Sentinel Team

Last Updated: 2026-03-04

Disclaimer: This article is for educational purposes only and does not constitute investment advice.

Want to learn more about blockchain applications? Sentinel Bot provides transparent, secure trading services based on blockchain technology.

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