Enforcing conditions on blockchain transactions

Computer equipment, comprising:

• memory comprising one or more memory units;
• and
• processing apparatus comprising one or more processing units, wherein the memory stores code arranged to run on the processing apparatus, the code being configured so as when run on the processing apparatus, the processing apparatus is configured to enforce conditions on a second blockchain transaction using a first blockchain transaction, wherein a first one of the conditions is that, when a first unlocking script of the second blockchain transaction is executed alongside a first locking script of the first blockchain transaction, a representation of the second blockchain transaction is output to memory, wherein the representation is based on a plurality of fields of the second blockchain transaction and a first output of the first blockchain transaction by:
• generating the first blockchain transaction, wherein the first blockchain transaction comprises a first output, wherein the first output comprises the first locking script, and wherein the first locking script comprises:
• a message sub-script constructed and arranged so as to, when executed by a blockchain node, cause the blockchain node to output to memory a candidate message representing the second blockchain transaction, wherein the candidate message is based on a plurality of candidate fields of the first and second blockchain transactions, wherein one or more of said candidate fields are included in the first unlocking script of the second blockchain transaction;
• a signature sub-script constructed and arranged so as to, when executed by a blockchain node, cause the blockchain node to generate a signature, wherein the signature is a function of at least the candidate message, a private key, and an ephemeral private key, and wherein the ephemeral private key is fixed by the first locking script as being equal to one and/or wherein the ephemeral private key is fixed as being equal to the private key;
• a public key corresponding to the private key;
• and
• a verification sub-script constructed and arranged so as to, when executed by a blockchain node, cause the blockchain node to i) construct a target message representing the second blockchain transaction, wherein the target message is based on a plurality of fields of the second blockchain transaction and the first output of the first blockchain transaction, and ii) use the public key to verify that the signature is valid for the target message, wherein verifying that the signature is valid for the target message, verifies that the target message matches the candidate message, thereby verifying that the candidate message output to memory is the representation of the second blockchain transaction.

A computer program embodied on non-transitory computer-readable storage media and configured so as, when run on one or more processors, the one or more processors perform a method of enforcing conditions on a second blockchain transaction using a first blockchain transaction, wherein a first one of the conditions is that, when a first unlocking script of the second blockchain transaction is executed alongside a first locking script of the first transaction, a representation of the second blockchain transaction is output to memory, wherein the representation is based on a plurality of fields of the second blockchain transaction and a first output of the first blockchain transaction, and wherein the method comprises:

• generating the first blockchain transaction, wherein the first blockchain transaction comprises a first output, wherein the first output comprises the first locking script, and wherein the first locking script comprises:
• a message sub-script constructed and arranged so as to, when executed by a blockchain node, cause the blockchain node to output to memory a candidate message representing the second blockchain transaction, wherein the candidate message is based on a plurality of candidate fields of the first and second blockchain transactions, wherein one or more of said candidate fields are included in the first unlocking script of the second blockchain transaction;
• a signature sub-script constructed and arranged so as to, when executed by a blockchain node, cause the blockchain node to generate a signature, wherein the signature is a function of at least the candidate message, a private key, and an ephemeral private key, and wherein the ephemeral private key is fixed by the first locking script as being equal to one and/or wherein the ephemeral private key is fixed as being equal to the private key;
• a public key corresponding to the private key;
• and
• a verification sub-script constructed and arranged so as to, when executed by a blockchain node, cause the blockchain node to i) construct a target message representing the second blockchain transaction, wherein the target message is based on a plurality of fields of the second blockchain transaction and the first output of the first blockchain transaction, and ii) use the public key to verify that the signature is valid for the target message, wherein verifying that the signature is valid for the target message, verifies that the target message matches the candidate message, thereby verifying that the candidate message output to memory is the representation of the second blockchain transaction.