PHOSDEEP / TECHNOLOGY / 05

BLOCKCHAIN · FROM FIRST PRINCIPLES

A LEDGER NOBODY OWNS.

Scroll to build one from nothing. No coins, no hype. Just the ideas that let strangers agree on what happened without trusting anyone in the middle.

01 / THE PROBLEM

EVERY RECORD HAS A KEEPER.

Your bank balance is a line in a ledger that one company keeps. Everyone connects to that one keeper and trusts it not to lose the record, edit it or switch it off. That keeper is a single point of failure, and a single point of control.

02 / THE IDEA

WHAT IF EVERYONE KEPT A COPY?

Remove the keeper. Give every participant, called a node, its own full copy of the ledger and connect the nodes to each other. Now no single machine can lose the record, censor it or quietly rewrite it. The hard part is keeping thousands of copies identical.

Hover or tap any node to inspect its copy.

03 / TRANSACTIONS

A MESSAGE, PASSED TO EVERYONE.

Alice wants to send Bob 0.5 units. She doesn't ask a bank. She signs a transaction and hands it to a few peers, who each pass it on to theirs. Within seconds, every node on the network has heard it.

Tap Alice's transaction to inspect it.

04 / KEYS & SIGNATURES

PROOF WITHOUT A PASSWORD.

How does the network know the message really came from Alice? She holds a private key, a secret 256-bit number. A public key is derived from it, and a short address from that. The math only runs one way, so she can prove the funds are hers without revealing the secret.

PRIVATE2bd8••••••••••••90ADDRESS0xfd50b11a…008c91

Simplified: real wallets derive the public key with elliptic-curve math (secp256k1), not a hash.

05 / HASHING

A FINGERPRINT FOR ANY DATA.

A hash function turns any input into a fixed 256-bit fingerprint. The same input always gives the same fingerprint. Change a single character and roughly half the bits flip. Try it.

INPUT · TYPE ANYTHING

SHA-256 OUTPUT

89d30af828cc8bef8aedf8c0f81c0e4b2b7b9a708b3f36846dbeb60382c413be

Change one character and watch the dial.

06 / BLOCKS

A BATCH, SEALED WITH ONE FINGERPRINT.

Nodes gather waiting transactions into a block. The transactions are hashed in pairs, then the pairs are hashed again, until a single Merkle root remains. The header stores that root next to the previous block's hash, a timestamp and a nonce.

Drag anywhere to orbit the block.

07 / THE CHAIN

EACH BLOCK POINTS TO THE LAST.

Every header contains the hash of the block before it. That single field turns separate blocks into a chain, and each new block seals everything that came before it.

08 / IMMUTABILITY

CHANGE ONE, BREAK THEM ALL.

Edit one old transaction and that block's hash changes, so it no longer matches the hash stored in the next block and the link snaps. To hide the edit you would have to rewrite every block after it faster than the rest of the network adds new ones.

Click any block to tamper with it. Editing #812,336

09 / CONSENSUS

WHO WRITES THE NEXT PAGE?

Proof of Work: miners race to find a nonce that gives the block a hash below a target. The only way is trillions of guesses. The winner's block is easy for everyone to check, and faking history would mean redoing all of that work.

10 / FORKS & FINALITY

WHEN TWO BLOCKS ARRIVE AT ONCE.

Sometimes two valid blocks appear at the same moment and the network briefly splits. Nodes keep building on whichever branch they saw first. The branch with the most work behind it wins and the other is orphaned. The deeper a block is buried, the more final it becomes.

canonical orphaned

11 / SMART CONTRACTS

CODE THAT KEEPS ITS PROMISES.

A blockchain can store programs as well as payments. This escrow contract holds the buyer's funds and releases them only when delivery is confirmed. No escrow agent is needed, because every node runs the same code and agrees on the result.

contract Escrow {  address buyer; address seller;  function deposit() payable {    require(msg.sender == buyer);    state = LOCKED;  }  function confirmDelivery() {    require(state == LOCKED);    seller.transfer(balance);  }}

12 / THE WHOLE LEDGER

HISTORY, HELD BY EVERYONE.

Millions of blocks, thousands of nodes, no owner. That's a blockchain: a shared record that is expensive to fake and cheap to verify.

SYNCING LEDGER

THE LAB · 01

BUILD A CHAIN BY HAND.

Four blocks, each sealed by proof of work. Change a single letter in any block and see what happens to everything after it. Then repair it the only way the network allows: by redoing the work.

THE LAB · 02

SIGN IT. THEN TRY TO FORGE IT.

A real key pair, generated in this tab. Sign a message with the private key, then play the attacker and change it on the way. Anyone holding only the public key can tell.

THE LAB · 03

RUN THE ESCROW CONTRACT.

Call the contract as the buyer or the seller. Calls that break a rule are reverted and change nothing, whoever makes them.

WHERE IT MATTERS

USEFUL WHEN NOBODY SHOULD BE IN CHARGE.

A blockchain is slower and costlier than an ordinary database. It's worth using when several parties need to share a record that none of them fully trusts the others to keep.

01
Payments & settlement
Moving value across borders in minutes instead of days, with a public record anyone can audit.
In production
02
Supply-chain provenance
Each hand-off is signed and stamped, so a product's journey from source to shelf can be verified.
In production
03
Digital identity & credentials
Degrees, licences and certificates you hold yourself, which anyone can check without calling the issuer.
Emerging
04
Tokenised assets
Bonds, funds and property represented as tokens that settle instantly and can be split into small pieces.
Scaling
05
Decentralised finance
Lending, exchange and escrow run as open smart contracts instead of as institutions.
Volatile
06
Tamper-evident records
Audit logs, land registries and public records where any silent edit is immediately visible.
Pilots

CAPABILITIES

WHAT
WE DO.

Blockchain Fundamentals

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Smart Contract Development

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Web3 Architecture

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Security Audits & Threat Modelling

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Tokenisation & Digital Assets

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Enterprise & Permissioned Ledgers

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