In-memory computation in homomorphic encryption systems

A computer system comprising:

• a homomorphic encryption system in which cryptographic elements are represented by polynomials with multibit coefficients, comprising an analog multiply-accumulate unit having at least one crossbar array of binary analog memory cells connected between respective pairs of word-lines and bit-lines of the at least one crossbar array, one or more computer readable storage media, and program instructions collectively stored on the one or more computer readable storage media for execution, the program instructions comprising:
• program instructions to store a matrix of multibit values for a computation in an analog multiply-accumulate unit comprising at least one crossbar array of binary analog memory cells connected between respective pairs of word-lines and bit-lines of the at least one crossbar array, wherein:
• bits of each multibit value are stored in cells connected along a word-line;
• and
• corresponding bits of values in a column of the matrix are stored in cells connected along a bit-line;
• program instructions to, in each of one or more computation stages for a cryptographic element, supply a set of polynomial coefficients of an element bitwise to respective word-lines of the analog multiplying-accumulate unit to obtain analog accumulation signals on the respective bit-lines;
• program instructions to convert the analog accumulation signals to digital signals;
• and
• program instructions to process the digital signals obtained from successive bits of the polynomial coefficients in each of the one or more computation stages to obtain a computation result for the cryptographic element.

A computer program product comprising:

• one or more computer readable storage media, and program instructions collectively stored on the one or more computer readable storage media, the program instructions comprising:
• program instructions to store a matrix of multibit values for a computation in an analog multiply-accumulate unit comprising at least one crossbar array of binary analog memory cells connected between respective pairs of word-lines and bit-lines of the at least one crossbar array, wherein:
• bits of each multibit value are stored in cells connected along a word-line;
• and
• corresponding bits of values in a column of the matrix are stored in cells connected along a bit-line;
• program instructions to, in each of one or more computation stages for a cryptographic element, supply a set of polynomial coefficients of an element bitwise to respective word-lines of the analog multiplying-accumulate unit to obtain analog accumulation signals on the respective bit-lines;
• program instructions to convert the analog accumulation signals to digital signals;
• and
• program instructions to process the digital signals obtained from successive bits of the polynomial coefficients in each of the one or more computation stages to obtain a computation result for the cryptographic element.