Blockchain-based atomic swap with veiled secret value exchange
A computer-implemented exchange method is provided. The method may be performed on one or more blockchains, such as the Bitcoin Cash blockchain. The method comprises the steps of: communicating a first veiled secret value from a first user to a second user and a second veiled secret value from the second user to the first user; and constructing first and second blockchain transactions each comprising the first veiled secret value and the second veiled secret value, the transactions arranged to be unlockable to transfer control of a respective first or second resource upon provision of both the first secret value and the second secret value to the respective blockchain transaction, wherein unlocking of the first blockchain transaction causes a first secret value to be revealed to the second user, and unlocking of the second blockchain transaction causes a second secret value to be revealed to the first user.
1. A computer-implemented exchange method, the method comprising:
(i) constructing a first blockchain transaction comprising a first veiled secret value communicated from a first user to a second user and a second veiled secret value communicated from the second user to the first user, the first blockchain transaction arranged to be unlockable to transfer control of a first resource upon provision of both a first masked secret value and a second masked secret value to the first blockchain transaction, wherein:
unlocking the first blockchain transaction causes the first masked secret value to be revealed to the second user; and
unlocking a second blockchain transaction causes the second masked secret value to be revealed to the first user, wherein the second blockchain transaction comprises the first veiled secret value and the second veiled secret value and is arranged to be unlockable to transfer control of a second resource upon provision of both the first masked secret value and the second masked secret value to the second blockchain transaction, wherein the first masked secret value is based on a first secret value and a shared secret value accessible by both the first user and second user, and the second masked secret value is based on a second secret value and the shared secret value accessible by both the first user and second user.
2. The computer-implemented exchange method according to claim 1 , wherein at least one of the first blockchain transaction or the second blockchain transaction is configured to be redeemable only upon application of a respective first private key and a respective second private key.
3. The computer-implemented exchange method according to claim 1 , further comprising calculating at least one of:
(a) a first derived public key based at least in part on a first public key of the first user, wherein the first derived public key is part of a cryptographic key pair with the respective first private key, or
(b) a second derived public key based at least in part on a second public key of the second user, wherein the second derived public key is part of a cryptographic key pair with the respective second private key.
4. The computer-implemented exchange method according to claim 3 , wherein calculating the first derived public key or the second derived public key is based at least in part on a combination of the first and second veiled secret values.
5. The computer-implemented exchange method according to claim 4 , wherein the combination of the first and second veiled secret values comprises at least one of:
a concatenation of the first veiled secret value and the second veiled secret value, or
a concatenation of at least one veiled secret value with a random or pseudorandom value.
6. The computer-implemented exchange method according to claim 1 , further comprising constructing at least one of:
a third blockchain transaction configured to return control of a first asset to the first user responsive to elapse of a first time period of non-redemption of the first blockchain transaction, or
a fourth blockchain transaction configured to return control of a second asset to the second user responsive to elapse of a second time period of non-redemption of the second blockchain transaction.
7. The computer-implemented exchange method according to claim 1 , wherein at least one of the first veiled secret value or the second veiled secret value comprises a combination of at least one of the first masked secret value or the second masked secret value with a shared secret value accessible by both the first user and the second user.
8. The computer-implemented exchange method according to claim 7 , wherein the shared secret value is established as a common secret (CS) prior to constructing the first blockchain transaction.
9. The computer-implemented exchange method according to claim 1 , further comprising:
(ii) generating at least one sequence of veiled secret values starting from at least one of the first secret value or the second secret value;
(iii) executing the computer-implemented exchange method using at least one of the first secret value or the second secret value; and
(iv) redeeming at least one blockchain transaction to reveal at least one of the first secret value or the second secret value, thereby causing at least one veiled secret value of the sequence to be revealed.
10. The computer-implemented exchange method according to claim 9 , wherein constructing the first blockchain transaction comprises constructing the first blockchain transaction using the at least one veiled secret value.
11. The computer-implemented exchange method according to claim 1 , further comprising communicating the first veiled secret value from the first user to the second user.
12. The computer-implemented exchange method according to claim 1 , further comprising receiving the second veiled secret value from the second user.