Mechanism LabONCHAIN MECHANICS
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ONCHAIN SYSTEMS · COURSE 001

A Ledger Everyone Can Verify

Start with one transfer that cannot be forged, replayed, or spent twice—not with consensus vocabulary.

4 lessonsabout 54 minbeginner friendly
Start lesson oneOpen sandbox ↗
COURSE EXAMPLEWhat makes everyone accept one transfer?

We split signatures, nonces, balances, transactions, and blocks into visible state transitions to see why nodes can reject tampering and replay.

PARTICIPANTS
  • YOUSender: authorize a state change with a key
  • TOReceiver: wait for the state to be written
  • NODENode: verify signature, nonce, and balance
  • BLKBlock: fix transaction order and state root
COURSE OUTLINE

One question per lesson

The lessons are ordered so that each one uses concepts introduced earlier.

  1. 01
    SIGNATURE · NONCE · STATE

    Who Authorized This Transfer?

    KEY QUESTIONWhy can a perfectly valid signature still produce a failed transaction?

    Follow a signed transaction into a block and see why tampering, replay, and balance violations are rejected.

    SignatureNonceTransactionBlockState root
    12 MIN
    →
  2. 02
    MEMPOOL · NONCE · REPLACEMENT

    Why Do Pending Transactions Queue?

    KEY QUESTIONTwo pending transactions share a nonce. Can both pay?

    Treat the transaction pool as a waiting room: see how one nonce can be replaced and why invalid transactions wait to be rejected.

    Transaction poolPendingReplacementNonce order
    13 MIN
    →
  3. 03
    ORDER · REPLAY · STATE ROOT

    Why Must the Same Transactions Have the Same Order?

    KEY QUESTIONHow can the same transaction set produce different balances when reordered?

    Replay a chain from genesis with block hashes and state roots, then see how nodes detect divergent execution.

    Transaction orderReplayState rootBlock hash
    15 MIN
    →
  4. 04
    CONFIRMATIONS · FINALITY

    What Is the Difference Between Confirmations and Finality?

    KEY QUESTIONWhy distinguish finality after many confirmations?

    Produce consecutive blocks and advance a simplified finality switch to separate ‘included’ from ‘safe to depend on’.

    ConfirmationsFinalitySafety bufferState dependency
    14 MIN
    →
WHAT IT COVERS

Questions covered in this course

01

What does a signature prove, and why can it not prove a sufficient balance?

02

How does a nonce stop the same transaction from executing twice?

03

How do balances and the state root change after a transaction enters a block?

04

Why are broadcasting, verification, packing, and finality different steps?