https://github.com/buzzcosm/udemy-course-blockchain-technology-in-java-1
Udemy course - Blockchain & Cryptocurrency in Java
https://github.com/buzzcosm/udemy-course-blockchain-technology-in-java-1
blockchain blockchain-demos blockchain-technology cryprocurrency cryptography java udemy-course-project
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Udemy course - Blockchain & Cryptocurrency in Java
- Host: GitHub
- URL: https://github.com/buzzcosm/udemy-course-blockchain-technology-in-java-1
- Owner: buzzcosm
- Created: 2025-05-04T17:56:45.000Z (about 1 month ago)
- Default Branch: main
- Last Pushed: 2025-05-04T20:59:56.000Z (about 1 month ago)
- Last Synced: 2025-05-04T21:32:57.756Z (about 1 month ago)
- Topics: blockchain, blockchain-demos, blockchain-technology, cryprocurrency, cryptography, java, udemy-course-project
- Language: Java
- Homepage:
- Size: 10.7 KB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# Udemy course - Blockchain
[learn blockchain technology in java](https://www.udemy.com/course/learn-blockchain-technology-in-java)
## Blockchain Theory and Implementation
Important Classes:
- [Block](./src/main/java/com/buzzcosm/blockchain/demo/Block.java)
- [Blockchain](./src/main/java/com/buzzcosm/blockchain/demo/Blockchain.java)
- [Miner](./src/main/java/com/buzzcosm/blockchain/demo/Miner.java)
### Proof of work (PoW) - Algorithm
```java
// This is a proof of work (PoW)
while (!isGoldenHash(block)) {
block.incrementNonce();
block.generateHash();
}
```
**Important terms:**
- **nonce**: number of tries to find a valid hash
- **difficulty**: number of leading zeros in hash
- **hash**: unique identifier of block
- **genesis block**: first block in blockchain
## Cryptocurrency
**Important terms:**
- **mempool**: transactions that have not been included in a block yet
- mempool **stores the transactions** until a given miner verifies them and puts them into a block
- similar to producer - consumer method
- **miner**: person who mines blocks
- **transaction**: transfer of funds between two parties
- **pre-verified** *transactions*: transactions that have already been verified and added to a block
- **transaction fee**: fee that is paid to the miner for including a transaction in a block
- **Merkle-Trees** Solution: https://en.wikipedia.org/wiki/Merkle_tree
- Merkle-Root
- Public & Private Key Cryptography
- Public Key Cryptography: https://en.wikipedia.org/wiki/Public-key_cryptography
- Private Key Cryptography: https://en.wikipedia.org/wiki/Private-key_cryptography
- Bitcoin: https://en.wikipedia.org/wiki/Bitcoin
- bitcoin protocol: https://en.bitcoin.it/wiki/Protocol_specification
- ECDSA (Elliptic Curve Digital Signature Algorithm): https://en.wikipedia.org/wiki/Elliptic_Curve_Digital_Signature_Algorithm
- Elliptic Curve Cryptography: https://en.wikipedia.org/wiki/Elliptic_Curve_Cryptography
- UTXOs (Unspent Transaction Output): https://en.wikipedia.org/wiki/Unspent_transaction_output
- Crypto Wallets: https://en.wikipedia.org/wiki/Crypto_wallet
- RIPEMD: https://en.wikipedia.org/wiki/RIPEMD
- 51% Attack: https://bitcoinwiki.org/wiki/51-attack
- competing chains problems
- double spending problems
- orphaned blocks & block verification
- Mining & Inflation
- Transaction Fees
- Blockchain Forks
- Soft Fork
- Hard Fork
> MINER'S REWARD = X BTC + TRANSACTION FEES
> TRANSACTION INPUT AMOUNT = TRANSACTION OUTPUT AMOUNT + MINER'S REWARD
### 51% Attack
- [YouTube: Was ist eine 51% Attacke? Einfach erklärt für Anfänger](https://www.youtube.com/watch?v=Dk3TrnU8kJU)
A 51% attack in blockchain refers to an attack where an attacker gains control of more than 50% of the network's hash rate, allowing them to manipulate the blockchain. This control enables them to alter transactions, double-spend funds, and potentially disrupt the entire network.
#### How a 51% attack works
1. Acquire control:
The attacker gathers enough computational power (hash rate) to surpass the network's majority.
2. Manipulate transactions:
They can then alter the order of transactions, prevent some from being confirmed, or even reverse valid transactions.
3. Double-spending:
The attacker can create a separate, fraudulent blockchain branch, which they can then broadcast to the network to invalidate the original transactions.
4. Disruption and loss of trust:
Successful 51% attacks can lead to double-spending, network instability, and a loss of trust in the cryptocurrency or blockchain.
Examples:
**Double-spending:**
An attacker could spend the same cryptocurrency twice, once in a real transaction and once on a fraudulent chain they create.
**Transaction manipulation:**
They could delay or prevent the confirmation of legitimate transactions, disrupting commerce.
**Block withholding:**
Attackers could mine blocks but withhold them from the network, leading to delays in block propagation and transaction confirmations.
#### Key takeaways
- A 51% attack poses a significant threat to Proof-of-Work (PoW) blockchain networks.
- The more hash rate a blockchain possesses, the harder it is to successfully launch a 51% attack.
- Successfully overcoming a 51% attack can be costly for the blockchain network and its users, leading to loss of trust and potential economic damage.