Cross-Chain Atomic Swap: HTLC Bridge Simulator

HTLC Atomic Swap

Timelock margin (Chain A vs Chain B) 6 blocks

Network latency 1.0×

Protocol State

1. Alice locks on Chain A (hash H, timelock T+48h)

2. Bob locks on Chain B (same H, timelock T+24h)

3. Alice reveals preimage S on Chain B, claims funds

4. Bob extracts S from Chain B, claims on Chain A

Secret / Hashlock

S = (not generated)
H = SHA256(S) = —

Elapsed (relative)

0.0 h

Swap status

Idle

Event Log

How it works

A Hash-Time-Locked Contract (HTLC) lets two chains that share no trust and no common consensus exchange value atomically — either both legs complete, or both refund, with no third party ever custodying funds:

1. Alice picks secret S, computes H = hash(S)
2. Alice locks funds on Chain A:
   "payable to whoever reveals S before T_A, else refund to Alice"
3. Bob sees H on Chain A, locks funds on Chain B:
   "payable to whoever reveals S before T_B, else refund to Bob"
   with T_B < T_A  (the safety margin this sim's slider controls)
4. Alice reveals S on Chain B to claim Bob's funds
   -> S is now public on Chain B
5. Bob reads S off Chain B, submits it to Chain A's contract
   before T_A, claiming Alice's funds

The timelock ordering (T_B strictly before T_A) is the safety property: it guarantees Bob always has enough time left to react on Chain A after seeing S revealed on Chain B, even under network delay. If Bob never locks, or Alice never reveals before her own deadline, every contract simply expires and refunds — no funds are ever lost, only time. This is the same primitive (with production hardening) used by the Lightning Network and most trust-minimized cross-chain bridges.

Timelock margin — the safety gap between Bob's deadline and Alice's; too small a margin risks Bob missing his claim window under real latency.
Network latency — scales how long each on-chain step visibly takes to propagate in the animation.
Bob Stalls — simulates Bob never locking on Chain B; Alice's HTLC simply times out and refunds, proving no funds were ever at risk.

Chain A ledger Chain B ledger In-flight packet

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