Block Chain Technologies (AL-802 (A)) Unit 5 Notes

How unit 5 is examined

This unit covers Hyperledger Fabric (architecture, identities, membership, channels, validation, chaincode), Ethereum smart contracts and Ripple/Corda; Fabric architecture and transaction validation carry the marks.

Hyperledger Fabric- Architecture

<span style="display:inline-block;padding:.16em .6em;border:1.5px solid currentColor;border-radius:999px;font-size:.68em;font-weight:700;letter-spacing:.06em;text-transform:uppercase;opacity:.75">High weight</span>

Definition. <mark>Hyperledger Fabric is an open-source, permissioned, modular enterprise blockchain platform, hosted by the Linux Foundation, in which known participants run peers that execute chaincode and an ordering service that sequences transactions.</mark>

Diagram. <figure class="ds-fig" style="margin:1.4rem 0;overflow-x:auto"><svg xmlns="http://www.w3.org/2000/svg" id="dsfig-u5-01" viewBox="0 0 431 252" width="431" height="252" role="img" aria-label="Fabric flow. App = client application, Peer = endorsing/committing peer, Ord = ordering service, Led = ledger (blockchain + world state)"><style>#dsfig-u5-01 .e{stroke:#454C5A;stroke-width:1.4;fill:none}#dsfig-u5-01 .e.hi{stroke:#2340B8;stroke-width:2.6}#dsfig-u5-01 .n{fill:#FFFFFF;stroke:#16181D;stroke-width:1.4}#dsfig-u5-01 .n.hi{fill:#E3E9FC;stroke:#2340B8;stroke-width:2.2}#dsfig-u5-01 .n.rb-b{fill:#16181D;stroke:#16181D}#dsfig-u5-01 .n.rb-r{fill:#BD3227;stroke:#BD3227}#dsfig-u5-01 text{font-family:"JetBrains Mono",ui-monospace,Menlo,Consolas,monospace;font-size:13px}#dsfig-u5-01 .t{fill:#16181D;font-weight:500}#dsfig-u5-01 .t.inv{fill:#FFFFFF;font-weight:700}#dsfig-u5-01 .kd{stroke:#16181D;stroke-width:1.2}#dsfig-u5-01 .dot{fill:#16181D}#dsfig-u5-01 .ann{fill:#2340B8;font-size:11px;font-weight:700}#dsfig-u5-01 .lbl{fill:#6F7787;font-family:system-ui,-apple-system,sans-serif;font-size:12px;font-weight:700}#dsfig-u5-01 .ptr{fill:#2340B8;font-size:12px;font-weight:700}#dsfig-u5-01 .ah{fill:#454C5A}#dsfig-u5-01 .ah.hi{fill:#2340B8}#dsfig-u5-01 .wl rect{fill:#FFFFFF;stroke:#DCE0E7}#dsfig-u5-01 .wl .t{font-size:12px;font-weight:700}#dsfig-u5-01 .wl.hi rect{fill:#2340B8;stroke:#2340B8}#dsfig-u5-01 .wl.hi .t{fill:#FFFFFF}html.dark #dsfig-u5-01 .e{stroke:#B1B7C3}html.dark #dsfig-u5-01 .e.hi{stroke:#8FA3FF}html.dark #dsfig-u5-01 .n{fill:#161920;stroke:#E6E8ED}html.dark #dsfig-u5-01 .n.hi{fill:#1E2748;stroke:#8FA3FF}html.dark #dsfig-u5-01 .n.rb-b{fill:#E6E8ED;stroke:#E6E8ED}html.dark #dsfig-u5-01 .n.rb-r{fill:#FF7E71;stroke:#FF7E71}html.dark #dsfig-u5-01 .t{fill:#E6E8ED}html.dark #dsfig-u5-01 .t.inv{fill:#0F1115}html.dark #dsfig-u5-01 .kd{stroke:#E6E8ED}html.dark #dsfig-u5-01 .dot{fill:#E6E8ED}html.dark #dsfig-u5-01 .ann{fill:#8FA3FF}html.dark #dsfig-u5-01 .lbl{fill:#858D9C}html.dark #dsfig-u5-01 .ptr{fill:#8FA3FF}html.dark #dsfig-u5-01 .ah{fill:#B1B7C3}html.dark #dsfig-u5-01 .ah.hi{fill:#8FA3FF}html.dark #dsfig-u5-01 .wl rect{fill:#161920;stroke:#2A2E37}html.dark #dsfig-u5-01 .wl.hi rect{fill:#8FA3FF;stroke:#8FA3FF}html.dark #dsfig-u5-01 .wl.hi .t{fill:#0F1115}</style><defs><marker id="ah5" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path class="ah" d="M0,1 L9,5 L0,9 z"/></marker><marker id="ahh5" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path class="ah hi" d="M0,1 L9,5 L0,9 z"/></marker></defs><path class="e" d="M58.8,123.3 Q140.3,111.6 192.2,59.8" marker-end="url(#ah5)"/><path class="e" d="M186.3,43.7 Q111.7,54.4 54.9,111.2" marker-end="url(#ah5)"/><path class="e" d="M57,134.5 L193.2,202.6" marker-end="url(#ah5)"/><path class="e" d="M212,193 L212,68" marker-end="url(#ah5)"/><path class="e" d="M238,40 L365,40"/><g class="wl"><rect x="102.2" y="92.6" width="61.5" height="18" rx="9"/><text class="t" x="132.9" y="101.6" dy=".35em" text-anchor="middle">propose</text></g><g class="wl"><rect x="85.4" y="56.9" width="61.5" height="18" rx="9"/><text class="t" x="116.1" y="65.9" dy=".35em" text-anchor="middle">endorse</text></g><g class="wl"><rect x="98.9" y="160" width="54.3" height="18" rx="9"/><text class="t" x="126" y="169" dy=".35em" text-anchor="middle">submit</text></g><g class="wl"><rect x="188.5" y="117" width="47.1" height="18" rx="9"/><text class="t" x="212" y="126" dy=".35em" text-anchor="middle">block</text></g><g class="wl"><rect x="270.9" y="31" width="54.3" height="18" rx="9"/><text class="t" x="298" y="40" dy=".35em" text-anchor="middle">commit</text></g><circle class="n" cx="40" cy="126" r="18"/><text class="t" x="40" y="126" dy=".35em" text-anchor="middle">App</text><rect class="n" x="187" y="25" width="50" height="30" rx="15"/><text class="t" x="212" y="40" dy=".35em" text-anchor="middle">Peer</text><circle class="n" cx="212" cy="212" r="18"/><text class="t" x="212" y="212" dy=".35em" text-anchor="middle">Ord</text><circle class="n" cx="384" cy="40" r="18"/><text class="t" x="384" y="40" dy=".35em" text-anchor="middle">Led</text></svg><figcaption style="font-size:.82em;opacity:.72;margin-top:.45rem">Fabric flow. App = client application, Peer = endorsing/committing peer, Ord = ordering service, Led = ledger (blockchain + world state)</figcaption></figure>

Key points.

Fabric is permissioned: every participant has a known identity issued by a Membership Service Provider, unlike Bitcoin or Ethereum where anyone can join anonymously.
Peers hold the ledger and run chaincode; endorsing peers simulate transactions and sign the result, and committing peers validate and write blocks.
The ordering service (orderers) sequences transactions into blocks and delivers them to peers, without executing them.
Chaincode is the smart contract, run in a Docker container, and it can be written in Go, Java or JavaScript instead of a single fixed language.
Channels give private sub-ledgers, so only the organisations on a channel see its transactions.
Fabric uses an execute-order-validate model, whereas public chains use order-execute, which lets it run non-deterministic-safe, parallel endorsement and higher throughput.
The design is modular: consensus (Raft), membership and endorsement policy can be plugged in.
There is no mining and no mandatory cryptocurrency, so transaction fees and energy cost are low.

Feature	Hyperledger Fabric	Bitcoin / Ethereum
Access	Permissioned, known identities	Public, anonymous
Consensus	Pluggable ordering (Raft)	PoW / PoS
Privacy	Channels, private data	All data public
Smart contract	Chaincode (Go, Java, JS)	Solidity on EVM
Currency	Optional	Native coin needed (BTC, ETH)
Throughput	High	Low

Answer frame. Open with the definition; draw the flow diagram; develop points 1-5 (peers, orderers, chaincode, channels, MSP); give the comparison table; close with "Fabric suits enterprise consortia needing privacy and speed". For "short notes" write 5 lines only.

Asked: [14 marks] (May 2022) Short notes: i) Hyperledger Fabric ii) Ripple and Corda iii) Cross border payments (Ripple/Corda and cross-border are under Ripple and Corda) Asked: [7 marks] (May 2024) What is Hyperledger Fabric and how does it differ from other blockchain platforms?

Identities and Policies

Definition. An identity is an X.509 digital certificate issued by a Certificate Authority that proves who a peer, orderer, admin or client is; a policy is a rule stating which identities must sign or may act.

Key points.

Every actor in Fabric holds a certificate with a private key, and each transaction is signed with it.
Endorsement policies state which organisations must endorse a transaction, for example "Org1 AND Org2".
Channel and access policies decide who may read, write or administer a channel.

Membership and Access Control

Definition. The Membership Service Provider (MSP) turns identities into organisation membership and roles, and access control lists (ACLs) use them to permit or deny actions.

Key points.

An MSP lists the root CA certificates of an organisation and defines its members, admins and peers.
Roles such as admin, peer, client and orderer decide what an identity may do.
ACLs attach policies to resources such as chaincode invocation or block events.
Because only enrolled members are admitted, the network is permissioned.

Channels

Definition. A channel is a private communication sub-network with its own separate ledger shared only by its member organisations.

Key points.

Each channel has its own ledger, members and chaincode, so data is isolated from other channels.
A peer can join several channels and keeps a separate ledger for each.
Channels give confidentiality in a consortium, for example two banks trading privately while a third sees nothing.
Private data collections give finer privacy inside a channel.

Transaction Validation

Definition. <mark>Transaction validation is the process of checking that a transaction is correctly signed, authorised and not a double spend before it is committed to the ledger.</mark>

Steps (Fabric).

Step 1: Client sends a proposal to endorsing peers, which simulate it and return signed read-write sets.
Step 2: Client submits the endorsed transaction to the ordering service.
Step 3: Orderers sequence transactions into a block and deliver it to all peers.
Step 4: Each peer checks the endorsement policy is satisfied and signatures are valid.
Step 5: Each peer checks read-set versions (MVCC) to detect conflicts or double spends.
Step 6: Valid transactions update the world state; invalid ones are marked and kept in the block.

Know Your Customer (KYC). KYC is the mandatory identity and address verification of a customer by a bank before service. On a blockchain, a customer is verified once, the verified record is shared through the ledger with permitted banks, and this removes repeated checks, cost and fraud.

Crypto currency. A crypto currency is digital money secured by cryptography, created and transferred on a decentralised blockchain without a central bank, for example Bitcoin. Ownership is proved by digital signatures and a consensus mechanism prevents double spending.

Creation of coin. New coins are created when a miner solves the proof-of-work puzzle and adds a block; the block reward is a special coinbase transaction. In Bitcoin the reward began at 50 BTC and halves every 210,000 blocks, which caps supply at 21 million.

Key points.

Validation checks digital signatures so only the owner spends a coin.
It checks that inputs are unspent, which prevents double spending.
In Bitcoin every full node validates each transaction and block independently.
In Fabric validation happens at commit time, after ordering.
Invalid transactions are rejected (Bitcoin) or flagged and not applied to state (Fabric).

Answer frame. Attempt any three terms; give each a definition line, the entities or steps involved, and one example; for transaction validation add the six-step list; close each term with its importance.

Asked: [14 marks] (May 2024) Explain any three: a) Transaction validation b) Know your customer c) Crypto currency d) Creation of coin

Writing smart contract using Hyperledger Fabric

Definition. A Fabric smart contract is chaincode, a program installed on peers that reads and writes the ledger world state through the chaincode API.

Key points.

It is written in Go, Java or JavaScript and runs in a Docker container.
Functions such as Init and Invoke use GetState and PutState to read and write key-value pairs.
It must be installed on peers, approved by organisations and committed to a channel before use.
It is executed by endorsing peers, and its result is validated later at commit.

Writing smart contract using Ethereum

Definition. <mark>A smart contract is self-executing code stored on the blockchain that enforces an agreement automatically when its conditions are met.</mark>

Key points.

On Ethereum, contracts are written in Solidity and compiled to bytecode that runs on the Ethereum Virtual Machine (EVM).
Deployment is a transaction that gives the contract an address; users then invoke its functions by sending transactions to that address.
Every operation costs gas, paid in ether, which stops infinite loops and pays miners.
Example uses: tokens, crowdfunding, voting and escrow.

contract Store { uint x; function set(uint v) public { x = v; } }

Asked: [7 marks] (May 2024) What is a smart contract and how is it used in the Ethereum blockchain?

Overview of Ripple and Corda

Definition. Ripple is a real-time gross settlement and payment network with the XRP token, and Corda is an R3 permissioned distributed ledger for financial agreements.

Key points.

Ripple uses the XRP Ledger consensus protocol among trusted validators, not mining, so settlement takes seconds at low cost.
Ripple targets cross-border payments: faster, cheaper settlement between banks without correspondent intermediaries.
Corda shares data only between parties to a deal, with no global broadcast, and uses notary nodes for consensus and uniqueness.
Corda contracts (CorDapps) are written in Kotlin or Java.

Last-minute revision

Fabric: permissioned, modular, peers + orderers + channels + chaincode, MSP identities.
Flow: execute (endorse), order, validate, commit.
Fabric uses Raft ordering, no mining, no mandatory coin.
Channel = private ledger for member organisations.
Endorsement policy states which organisations must sign.
Validation checks signatures, unspent inputs and MVCC versions.
KYC = verify customer identity once, share through ledger.
Bitcoin reward halves every 210,000 blocks; supply cap 21 million.
Smart contract = self-executing code; Ethereum uses Solidity, EVM and gas.
Ripple = XRP payments consensus; Corda = notary, need-to-know sharing.

Memory hooks

Fabric flow: "E-O-V" = Execute, Order, Validate.
MSP = "Who are you?"; Channel = "Who may see?"; Policy = "Who must sign?".
Gas = fuel for the EVM.
Ripple = Real-time payments; Corda = Confidential deals.

Coverage checklist

Hyperledger Fabric- Architecture: May 2022 short notes (Fabric), May 2024 comparison.
Identities and Policies: no past questions.
Membership and Access Control: no past questions.
Channels: no past questions.
Transaction Validation: May 2024 any three terms (validation, KYC, crypto currency, creation of coin).
Writing smart contract using Hyperledger Fabric: no past questions.
Writing smart contract using Ethereum: May 2024 smart contract in Ethereum.
Overview of Ripple and Corda: May 2022 short notes (Ripple and Corda, cross border payments).

Account

Block Chain Technologies (AL-802 (A)) - Unit 5 Short Notes

How unit 5 is examined

Hyperledger Fabric- Architecture

Identities and Policies

Membership and Access Control

Channels

Transaction Validation

Writing smart contract using Hyperledger Fabric

Writing smart contract using Ethereum

Overview of Ripple and Corda

Last-minute revision

Memory hooks

Coverage checklist