Blockchain and Public Ledger
Distributed ledger technology that uses cryptographic hashing to create tamper-evident chains of records. Each block contains a hash of the previous block, creating integrity through cryptographic linking.
Understanding Blockchain and Public Ledger
Blockchain is a distributed ledger that maintains an immutable record of transactions using cryptographic hashing. Each block contains data, a timestamp, and—critically—a hash of the previous block, creating a chain where altering any block invalidates all subsequent blocks.
Key security properties: • Immutability — Past records cannot be changed without detection • Transparency — All participants can verify the ledger • Decentralization — No single point of control or failure • Integrity — Cryptographic hashes ensure data hasn't been altered
While blockchain is famous for cryptocurrency, its security applications include supply chain tracking, digital voting, identity management, and audit trails.
Why This Matters for the Exam
SY0-701 tests blockchain as a cryptographic concept—how hashing creates integrity, not cryptocurrency investment. Questions focus on the security properties blockchain provides and appropriate use cases.
Understanding blockchain helps with questions about distributed systems, integrity verification, and decentralized trust. The cryptographic principles (hashing, linking) are testable concepts.
Blockchain also demonstrates practical application of hashing for integrity—a concept that appears throughout security.
Deep Dive
How Blockchain Works
Block Structure:
- •Data (transactions, records)
- •Timestamp
- •Hash of this block
- •Hash of previous block
- •Nonce (for proof of work)
Chain Formation:
- •```
- •Block 1 → Block 2 → Block 3
- •[Hash: abc] → [Prev: abc, Hash: def] → [Prev: def, Hash: ghi]
- •```
Tamper Detection:
- •Change data in Block 2
- •Block 2's hash changes
- •Block 3's "previous hash" no longer matches
- •Chain broken → Tampering detected
Public Ledger Concept
A public ledger is a transparent record viewable by all participants.
Characteristics:
- •Open to inspection
- •No central authority controls it
- •Participants validate entries
- •Distributed copies prevent single point of failure
Public vs. Private Blockchain:
| Type | Access | Validation | Use Case |
|---|---|---|---|
| Public | Anyone can join | Open consensus | Cryptocurrency, public records |
| Private | Restricted access | Selected validators | Enterprise, supply chain |
| Consortium | Multiple organizations | Shared governance | Industry collaboration |
Cryptographic Components
Hashing
- •Each block contains hash of its contents
- •Any data change produces different hash
- •Links blocks in tamper-evident chain
Digital Signatures
- •Transactions signed by participants
- •Proves authorization and authenticity
- •Non-repudiation for actions
Asymmetric Cryptography
- •Public/private keys for identity
- •Addresses derived from public keys
- •Private keys authorize transactions
Consensus Mechanisms
How decentralized networks agree on valid blocks:
Proof of Work (PoW)
- •Miners solve computational puzzles
- •First to solve adds the block
- •Energy-intensive but proven
- •Used by Bitcoin
Proof of Stake (PoS)
- •Validators stake cryptocurrency
- •Selected to add blocks based on stake
- •More energy-efficient
- •Used by Ethereum (now)
Practical Byzantine Fault Tolerance (PBFT)
- •Voting among known validators
- •Faster than PoW/PoS
- •Used in private blockchains
Security Applications of Blockchain
Supply Chain Integrity
- •Track products from origin to consumer
- •Immutable record of handling
- •Detect tampering or counterfeiting
Identity Management
- •Self-sovereign identity
- •Verifiable credentials
- •Decentralized authentication
Audit Trails
- •Immutable log of events
- •Regulatory compliance
- •Forensic investigation
Digital Voting
- •Transparent vote recording
- •Verifiable results
- •Tamper-resistant tallies
Blockchain Limitations
• Scalability — Transaction throughput limited • Energy — PoW is energy-intensive • Immutability trade-off — Can't fix errors • Privacy challenges — Public chains expose data • Complexity — Not always the right solution
How CompTIA Tests This
Example Analysis
Scenario: An organization needs to maintain an audit log of sensitive financial transactions. The log must be tamper-evident—any modifications should be detectable—and multiple parties need to verify the records independently.
Solution: Blockchain-based Audit Trail
Why Blockchain: • Tamper-evident: Hash chains detect any modification • Distributed: Multiple parties have copies • Verifiable: Each party can independently verify integrity • Non-repudiation: Digital signatures on transactions
Implementation: • Private/consortium blockchain among auditors • Each transaction signed and recorded • Hash linking ensures integrity • Distributed copies prevent single point of manipulation
Why NOT traditional database: • Central DB admin could modify records • Single copy can be altered without detection • No cryptographic integrity guarantees
Key insight: Blockchain's value here isn't cryptocurrency—it's the cryptographic integrity and distributed verification that traditional systems lack.
Key Terms to Know
Common Mistakes to Avoid
Exam Tips
Memory Trick
"ITDI" - Blockchain Security Properties
- •Immutability — Can't change past records
- •Transparency — Everyone can see/verify
- •Decentralization — No single point of control
- •Integrity — Hashes ensure data unchanged
Chain Linking Memory: Each block holds the PREVIOUS block's hash Change one block → All following blocks invalid Like a chain of paper clips—remove one, chain breaks
Hash Chain Visual: Block 1 [Hash: A] → Block 2 [Prev: A, Hash: B] → Block 3 [Prev: B, Hash: C] Modify Block 1 → Hash changes from A to X → Block 2's "Prev: A" no longer matches → DETECTED!
- •Public vs. Private:
- •Public = Open party (anyone comes)
- •Private = Private party (invitation only)
Test Your Knowledge
Q1.How does blockchain detect tampering of data in previous blocks?
Q2.What is a key characteristic of a public ledger in blockchain?
Q3.Which security property does blockchain's hash-chain structure primarily provide?
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