Identity-based public-key generation protocol

A computer-implemented method for generating an identity-based cryptographic key, wherein a first party has a personal identifier, and wherein the method is performed by a first key-generating party and comprises:

• transmitting a private key share to the first party, wherein the private key share is generated based on the personal identifier of the first party and has a corresponding public key share;
• obtaining a partial identity-based public key, based on the corresponding public key share, wherein the partial identity-based public key does not correspond to the identity-based private key;
• generating and/or obtaining the complete identity-based public key, wherein the complete identity-based public key is generated based on the partial identity-based public key and the personal identifier, and wherein the complete identity-based public key corresponds to the identity-based private key;
• and
• generating a first blockchain transaction comprising a first output that comprises the complete identity-based public key.

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 on the processing apparatus to perform a method of generating an identity-based cryptographic key, the method being performed by a first party having a personal identifier, and comprising:
• obtaining a set of private key shares and a set of corresponding public key shares, wherein each private key share is generated based on the personal identifier of the first party, and wherein at least one of the set of private key shares is generated by a respective one of a set of key-generating parties;
• generating an identity-based private key based on each of the one or more private key shares;
• and
• generating a partial identity-based public key based on each of the set of corresponding public key shares, wherein the partial identity-based public key does not correspond to the identity-based private key;
• and
• wherein the method also comprises;
• transmitting the partial identity-based public key to at least one of the set of key-generating parties for generating the a complete identity-based public key, wherein the complete identity-based public key comprises the personal identifier and the partial identity-based public key;
• and/or
• generating the complete identity-based public key based on the personal identifier and the partial identity-based public key, wherein the complete identity-based public key corresponds to the identity-based private key;
• and
• wherein the method further comprises:
• i) encrypting a first message using the complete identity-based public key to generate a first encrypted message;
• and
• transmitting the first encrypted message to a second party, and/or generating a second blockchain transaction comprising an output that comprises the encrypted message;
• or
• ii) obtaining a second encrypted message encrypted using the complete identity-based public key;
• and decrypting the second encrypted message using the private key to reveal a second message.

A computer program embodied on computer-readable storage and configured so as, when run on computer equipment, to perform a method of generating an identity-based cryptographic key, the method being performed by a first party having a personal identifier, and comprising:

• obtaining a set of private key shares and a set of corresponding public key shares, wherein each private key share is generated based on the personal identifier of the first party, and wherein at least one of the set of private key shares is generated by a respective one of a set of key-generating parties;
• generating an identity-based private key based on each of the one or more private key shares;
• and
• generating a partial identity-based public key based on each of the set of corresponding public key shares, wherein the partial identity-based public key does not correspond to the identity-based private key;
• and
• wherein the method also comprises;
• transmitting the partial identity-based public key to at least one of the set of key-generating parties for generating the a complete identity-based public key, wherein the complete identity-based public key comprises the personal identifier and the partial identity-based public key;
• and/or
• generating the complete identity-based public key based on the personal identifier and the partial identity-based public key, wherein the complete identity-based public key corresponds to the identity-based private key;
• and
• wherein the method further comprises:
• i) encrypting a first message using the complete identity-based public key to generate a first encrypted message;
• and
• transmitting the first encrypted message to a second party, and/or generating a second blockchain transaction comprising an output that comprises the encrypted message;
• or
• ii) obtaining a second encrypted message encrypted using the complete identity-based public key;
• and decrypting the second encrypted message using the private key to reveal a second message.