[Resource Topic] 2024/1201: Designing a General-Purpose 8-bit (T)FHE Processor Abstraction

Welcome to the resource topic for 2024/1201

Title:
Designing a General-Purpose 8-bit (T)FHE Processor Abstraction

Authors: Daphné Trama, Pierre-Emmanuel Clet, Aymen Boudguiga, Renaud Sirdey

Abstract:

Making the most of TFHE programmable bootstrapping to evaluate functions or operators otherwise difficult to perform with only the native addition and multiplication of the scheme is a very active line of research. In this paper, we systematize this approach and apply it to build an 8-bit FHE processor abstraction, i.e., a software entity that works over FHE-encrypted 8-bits data and presents itself to the programmer by means of a conventional-looking assembly instruction set. In doing so, we provide several homomorphic LUT dereferencing operators based on variants on the tree-based method and show that they are the most efficient option for manipulating encryptions of 8-bit data (optimally represented as two base 16 digits). We then systematically apply this approach over a set of around 50 instructions, including, notably, conditional assignments, divisions, or fixed-point arithmetic operations. We then conclude the paper by testing the approach on several simple algorithms, including the execution of a neuron with a sigmoid activation function over 16-bit precision. Finally, this work reveals that a very limited set of functional bootstrapping patterns is versatile and efficient enough to achieve general-purpose FHE computations beyond the boolean circuit approach. As such, these patterns may be an appropriate target for further works on advanced software optimizations or hardware implementations.

ePrint: https://eprint.iacr.org/2024/1201

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