In this track: Smart contract security foundations
advanced · 4 MIN READ
Flash loans as a mechanism
Atomic borrowing changes available temporary capital, not arithmetic truth.
LET’S PICTURE IT
A borrower can use resources during one all-or-nothing procedure if repayment conditions are met.
SEE IT FOR YOURSELF
A valid counter call, step by stepStep 1 / 4
This example begins with count zero and a request to call increment(). No real contract is deployed.
This example begins with count zero and a request to call increment(). No real contract is deployed.Execution follows the code’s input and permission rules. A website button is not the access-control mechanism.The function reads zero, calculates zero plus one, and writes one to persistent storage.The accepted state contains count one. Later reads can inspect it. Events are emitted only if the code implements them.
Animated local teaching model. No wallet, RPC or live blockchain data. Some labels and hashes are abbreviated for readability.
Understand atomic repayment
A flash-loan protocol makes funds available during a transaction and checks repayment conditions before accepting the final execution. Failure typically reverts the enclosing workflow.
Separate mechanism from vulnerability
Temporary capital can support legitimate operations. A harmful result depends on a separate weakness such as unsafe price assumptions or inconsistent accounting.
Test without assuming small balances
A protocol should not rely on an adversary lacking enough temporary capital unless that assumption is explicitly justified. Model large local balances in tests.
Preserve the full fee and callback context
The provider defines fees, callback authentication and repayment details. A generic flash-loan description is not sufficient to implement any particular provider’s interface.
Reason about the scenario
borrow → callback actions → repayment check
all conditions pass → transaction can succeed
repayment fails → workflow reverts
Pseudocode or a simplified scenario for local reasoning. This is not a production contract or a completed security review.
QUICK CHECK · NO PRESSURE
Does a flash loan itself make an incorrect price mathematically correct?
It changes temporary resources, not the validity of an accounting assumption.