Blockchain based read receipt

A computer-implemented method of sending a read receipt for a message using a blockchain, the read receipt evidencing that the message has been opened, the method being performed by a second party and comprising:

• receiving a message, and/or an encrypted version thereof;
• identifying a request blockchain transaction, wherein the request blockchain transaction comprises a first output locked by a first locking script, wherein the first locking script is configured to, when executed together with a first unlocking script of a response blockchain transaction, require the first unlocking script to comprise a solution to a cryptographic puzzle, wherein the locking script comprises a conditional clause, which is configured to require the first unlocking script of the response transaction to further comprise either i) a signature generated based on a first hash, or ii) a signature that is not generated based on the first hash, and wherein the first unlocking script comprises either signature;
• generating the solution to the cryptographic puzzle, wherein the solution is based on the message, and wherein the solution to the cryptographic puzzle requires knowledge of the first hash based on the message;
• generating a first signature based on the first hash or a second signature that is not generated based on the first hash;
• generating a response blockchain transaction, wherein generating the response blockchain transaction comprises:
• generating a first input of the response blockchain transaction that includes a first unlocking script and a reference to the first output of the request transaction;
• including the solution to the cryptographic puzzle in the first unlocking script;
• including the first or second signature in the first unlocking script;
• and
• causing the response blockchain transaction to be submitted to a blockchain network.

A non-transitory computer readable medium comprising a computer program configured so as, when run on one or more processors, the one or more processors perform a method of requesting a read receipt for a message using a blockchain, the read receipt evidencing that the message has been opened, the method being performed by a first party and comprising:

• sending the message, and/or an encrypted version thereof, to a second party:
• generating a cryptographic puzzle based on the message, including generating a first hash based on the message by performing a cryptographic hashing operation on the message;
• generating a request blockchain transaction, wherein generating the request blockchain transaction comprises:
• generating a first output of the request blockchain transaction;
• constructing a first locking script that is configured to, when executed together with a first unlocking script of a response blockchain transaction, require the first unlocking script to comprise a solution to the cryptographic puzzle,
• wherein constructing the first locking script comprises constructing a conditional clause sub-script that is configured to require the first unlocking script of the response transaction to further comprise either i) a signature generated based on the first hash, or ii) a signature generating using a private key corresponding to a public key associated with the second party;
• causing the request blockchain transaction to be submitted to a blockchain network;
• determining that the first output of the request blockchain transaction has been unlocked;
• and
• determining that the message has been opened in response to determining that the first output has been unlocked.