Inter stage key-switching-key reuse

A non-transitory computer-readable medium storing a set of instructions for determining a set of key-switching keys (KSK) to be used in linear transformations of both Discrete Fourier Transform (DFT) and Inverse Discrete Fourier Transform (IDFT) matrices of a slots-to-coefficients (S2C) stage and a coefficient-to-slots (C2S) stage, the set of instructions comprising:

• one or more instructions that, when executed by one or more processors of a device, cause the device to:
• select decomposition parameters based on an optimization technique, wherein the optimization technique utilizes a predetermined lookup table that maps hardware constraint indicators to appropriate values of the decomposition parameters, and decompose the DFT and IDFT matrices in accordance with the decomposition parameters into a plurality of merged nonzero submatrices;
• determine rotation offsets of the plurality of merged nonzero submatrices to enable an optimal number of rotations in the S2C stage to overlap with rotations in the C2S stage;
• calculate an effective set of KSKs;
• and
• load the effective set of KSKs to an internal memory of a hardware accelerator at an initialization stage of a Fully Homomorphic Encryption (FHE) program, wherein the internal memory is a dedicated memory used by a processor of the hardware accelerator to store data for executing the FHE program and routines including bootstrapping and linear transformation.

A system for determining a set of key-switching keys (KSK) to be used in linear transformations of both Discrete Fourier Transform (DFT) and Inverse Discrete Fourier Transform (IDFT) matrices of a slots-to-coefficients (S2C) stage and a coefficient-to-slots (C2S) stage comprising:

• one or more processors configured to:
• select decomposition parameters based on an optimization technique, wherein the optimization technique utilizes a predetermined lookup table that maps hardware constraint indicators to appropriate values of the decomposition parameters, and decompose the DFT and IDFT matrices in accordance with the decomposition parameters into a plurality of merged nonzero submatrices;
• determine rotation offsets of the plurality of merged nonzero submatrices to enable an optimal number of rotations in the S2C stage to overlap with rotations in the C2S stage;
• calculate an effective set of KSKs;
• and
• load the effective set of KSKs to an internal memory of a hardware accelerator at an initialization stage of a Fully Homomorphic Encryption (FHE) program, wherein the internal memory is a dedicated memory used by a processor of the hardware accelerator to store data for executing the FHE program and routines including bootstrapping and linear transformation.