Low bandwidth rotation keys generation for a hierarchical threat model

A computer program product for low bandwidth homomorphic encryption (HE) processor, comprising a computer readable storage medium having program instructions embodied therewith, the program instructions executable by a processor to cause the processor to:

• generate, at a principal instance of an organization unit, a principal HE key set, wherein the principal HE key set comprises a principal HE public key, a principal HE secret key, a principal HE evaluation key, and a plurality of principal HE rotation keys;
• generate a department HE key set for each of a plurality of departments in the organization unit, wherein the set of department HE encryption keys each comprises a department HE public key, a department HE secret key, a department HE evaluation key, and a department HE key switching key;
• transmit the principal public HE key, the principal HE evaluation key, and the plurality of principal HE rotation keys to a data processor;
• transmit, by at least one of the plurality of departments to the data processor, at least one department public HE key, department evaluation key, and department key switching HE key to the data processor;
• and
• transmit, by the at least one of the plurality of departments to the data processor, an encrypted data file to be processed at least in part using a department HE rotation key generated at the data processor.

A homomorphic encryption (HE) system, comprising at least one processor configured to execute program instructions that, when executed on the processor, cause the processor to:

• generate, at a principal instance of an organization unit, a principal HE key set, wherein the principal HE key set comprises a principal HE public key, a principal HE secret key, a principal HE evaluation key, and a plurality of principal HE rotation keys;
• generate a department HE key set for each of a plurality of departments in the organization unit, wherein the set of department HE encryption keys each comprises a department HE public key, a department HE secret key, a department HE evaluation key, and a department HE key switching key;
• transmit the principal public HE key, the principal HE evaluation key, and the plurality of principal HE rotation keys to a data processor;
• transmit, by at least one of the plurality of departments to the data processor, at least one department public HE key, department evaluation key, and department key switching HE key to the data processor;
• and
• transmit, by the at least one of the plurality of departments to the data processor, an encrypted data file to be processed at least in part using a department HE rotation key generated at the data processor.