Block chain

- Block chain is a database
- Bespoke data structure

"Not crpyto"

General Purpose block chain:

Why?
- Data in block is immutable
- Don't edit or remove, you append
- traceability (Auditing / logging)
- Verifiability (Data must be fully valid)
- reproducibility
- decentralisation
- Trust-less (Removes need for trust)
- transparency

How?
- What type?
    - public - will be hacked
    - shared - shared ledger
    - private
- Cryptography
    - pub/rivate keys
    - sign information
    - verifablity
    - Elliptic Curves
    - openssl ecparam -list_curves
    - Addressing
        - can shorten public keys massively
    - Hash algorithm
        - Integrity
        - 2x sha256 (sha256(sha256($data)))
        - 4B version, 32B hash of  last Block, 32B  hash of data block, 4B timestamp, 4B difficulty, 4B nonce
        - Merkle tree - binary hash tree
        - Merkle path - list of hashes through the tree
        - Genesis block - First block in the chain
            - Special as it's first
            - Prevents exploitation by being hardcoded

- consensus
    - Confidence
    - chain forking needs resolution
        - bitcoin users longest chain wins
        - proof of work / proof of stake
        - difficulty is no of zeros  that need to be at the start of the hash
        - others (proof of burn, proof of time, proof of ....)


- Smart contracts
    - Programs that are included in the chain
    - e.g. A loan paid by the chain

- Lighting network (drawback off blockhain is it focuses on integrity not perf)
    - Off chain transactions with on-chain settlement

- Not all blockchains are chains
    - IOTA Tangle

- Challenges
    - Fault tolerance
        - You lose control of public/shared blockchains
        - Now way to enforce software updates
        - Conflict resolution
    - Integration with current systems
    - Security
        - Cryptography is first and last line of defence

- Not perfect for:
    - scalability
    - performance
    - throughput

- Incentives
    - Mining in currencies
        - Power for money
- Privacy
    - Protect data

- Hard forks
- 51% attacks

- Right solution for the right kind of problem

- Event sourcing on steroids

QUESTIONS
- Any php recommendations?
    - No.
- security?
    - Store data not values somewhere else
    - Encrypt
- Why private blocks?
    - Can give public list of hashes for verification
    - keep data private