mirror of
https://github.com/bitcoin/bips.git
synced 2024-11-19 01:40:05 +01:00
81 lines
3.7 KiB
Plaintext
81 lines
3.7 KiB
Plaintext
<pre>
|
|
BIP: 199
|
|
Layer: Applications
|
|
Title: Hashed Time-Locked Contract transactions
|
|
Author: Sean Bowe <sean@z.cash>
|
|
Daira Hopwood <daira@z.cash>
|
|
Comments-Summary: No comments yet.
|
|
Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-0199
|
|
Status: Draft
|
|
Type: Standards Track
|
|
Created: 2017-03-27
|
|
License: BSD-3-Clause
|
|
CC0-1.0
|
|
</pre>
|
|
|
|
==Abstract==
|
|
|
|
This BIP describes a script for generalized off-chain contract negotiation.
|
|
|
|
==Summary==
|
|
|
|
A Hashed Time-Locked Contract (HTLC) is a script that permits a designated party (the "seller") to spend funds by disclosing the preimage of a hash. It also permits
|
|
a second party (the "buyer") to spend the funds after a timeout is reached, in a refund situation.
|
|
|
|
The script takes the following form:
|
|
|
|
OP_IF
|
|
[HASHOP] <digest> OP_EQUALVERIFY OP_DUP OP_HASH160 <seller pubkey hash>
|
|
OP_ELSE
|
|
<num> [TIMEOUTOP] OP_DROP OP_DUP OP_HASH160 <buyer pubkey hash>
|
|
OP_ENDIF
|
|
OP_EQUALVERIFY
|
|
OP_CHECKSIG
|
|
|
|
[HASHOP] is either OP_SHA256 or OP_HASH160.
|
|
|
|
[TIMEOUTOP] is either OP_CHECKSEQUENCEVERIFY or OP_CHECKLOCKTIMEVERIFY.
|
|
|
|
===Interaction===
|
|
|
|
* Victor (the "buyer") and Peggy (the "seller") exchange public keys and mutually agree upon a timeout threshold. Peggy provides a hash digest. Both parties can now construct the script and P2SH address for the HTLC.
|
|
* Victor sends funds to the P2SH address.
|
|
* Either:
|
|
** Peggy spends the funds, and in doing so, reveals the preimage to Victor in the transaction; OR
|
|
** Victor recovers the funds after the timeout threshold.
|
|
|
|
Victor is interested in a lower timeout to reduce the amount of time that his funds are encumbered in the event that Peggy does not reveal the preimage. Peggy is
|
|
interested in a higher timeout to reduce the risk that she is unable to spend the funds before the threshold, or worse, that her transaction spending the funds does
|
|
not enter the blockchain before Victor's but does reveal the preimage to Victor anyway.
|
|
|
|
==Motivation==
|
|
|
|
In many off-chain protocols, secret disclosure is used as part of a settlement mechanism. In some others, the secrets themselves are valuable. HTLC transactions are
|
|
a safe and cheap method of exchanging secrets for money over the blockchain, due to the ability to recover funds from an uncooperative counterparty, and the
|
|
opportunity that the possessor of a secret has to receive the funds before such a refund can occur.
|
|
|
|
===Lightning network===
|
|
|
|
In the lightning network, HTLC scripts are used to perform atomic swaps between payment channels.
|
|
|
|
Alice constructs K and hashes it to produce L. She sends an HTLC payment to Bob for the preimage of L. Bob sends an HTLC payment to Carol for the same preimage and
|
|
amount. Only when Alice releases the preimage K does any exchange of value occur, and because the secret is divulged for each hop, all parties are compensated. If
|
|
at any point some parties become uncooperative, the process can be aborted via the refund conditions.
|
|
|
|
===Zero-knowledge contingent payments===
|
|
|
|
Various practical zero-knowledge proving systems exist which can be used to guarantee that a hash preimage derives valuable information. As an example, a
|
|
zero-knowledge proof can be used to prove that a hash preimage acts as a decryption key for an encrypted sudoku puzzle solution. (See
|
|
[https://github.com/zcash/pay-to-sudoku pay-to-sudoku] for a concrete example of such a protocol.)
|
|
|
|
HTLC transactions can be used to exchange such decryption keys for money without risk, and they do not require large or expensive-to-validate transactions.
|
|
|
|
==Implementation==
|
|
|
|
https://github.com/bitcoin/bitcoin/pull/7601
|
|
|
|
==Copyright==
|
|
|
|
This document is dual licensed as BSD 3-clause, and Creative Commons CC0 1.0 Universal.
|
|
|