Method and system for communicating a secret

A method of receiving a secret sent from a sender to a recipient, each having a respective public key/private key pair, the method comprising:

• receiving, at the recipient, information identifying a plurality of secrets selectable by the recipient;
• generating a third secret, to be shared between the sender and the recipient, from the respective public key/private key pairs held by the sender and recipient;
• generating, at the recipient, a first public key, a first private key corresponding to the first public key, and a second public key, all being of an elliptic curve cryptography system, wherein the first public key is generated from the recipient's respective public key/private key pair, the first private key is based on the first public key, the second public key is based on the first public key/first private key pair and the third secret, and a second private key corresponding to the second public key is not known to the recipient
• sending, to the sender, from the recipient, the first public key, corresponding to a first secret, of the plurality of secrets, selected for access by the recipient;
• sending, to the sender, from the recipient, the second public key, corresponding to a second secret, of the plurality of secrets, not selected for access by the recipient;
• receiving, at the recipient from the sender, a first secret encrypted by means of the corresponding first public key;
• and
• receiving, at the recipient from the sender, a second secret encrypted by means of the corresponding second public key,
• wherein the first secret is accessible to the recipient by means of the corresponding first private key, the second secret is inaccessible to the recipient, and the sender is unable to distinguish between the first secret and the second secret.

A computer-implemented comprising:

• a processor;
• and
• non-transitory computer-readable memory with instructions that, if executed by the processor, cause the system to:
• receive, at a recipient having a respective public key/private key pair, information identifying a plurality of secrets selectable by the recipient;
• generate a third secret, to be shared between a sender having a respective public key/private key pair, and the recipient, from the respective public key/private key pairs held by the sender and recipient;
• generate, at the recipient, a first public key, a first private key corresponding to the first public key, and a second public key, all being of an elliptic curve cryptography system, wherein the first public key is generated from the recipient's respective public key/private key pair, the first private key is based on the first public key, the second public key is based on the first public key/first private key pair and the third secret, and a second private key corresponding to the second public key is not known to the recipient
• send, to the sender, from the recipient, the first public key, corresponding to a first secret, of the plurality of secrets, selected for access by the recipient;
• send, to the sender, from the recipient, the second public key, corresponding to a second secret, of the plurality of secrets, not selected for access by the recipient;
• receive, at the recipient from the sender, a first secret encrypted by means of the corresponding first public key;
• and
• receive, at the recipient from the sender, a second secret encrypted by means of the corresponding second public key,
• wherein the first secret is accessible to the recipient by means of the corresponding first private key, the second secret is inaccessible to the recipient, and the sender is unable to distinguish between the first secret and the second secret.