The migration of computation to the cloud has raised privacy concerns as
sensitive data becomes vulnerable to attacks since they need to be decrypted
for processing. Fully Homomorphic Encryption (FHE) mitigates this issue as it
enables meaningful computations to be performed directly on encrypted data.
Nevertheless, FHE is orders of magnitude slower than unencrypted computation,
which hinders its practicality and adoption. Therefore, improving FHE
performance is essential for its real world deployment. In this paper, we
present a year-long effort to design, implement, fabricate, and post-silicon
validate a hardware accelerator for Fully Homomorphic Encryption dubbed CoFHEE.
With a design area of 12mm2, CoFHEE aims to improve performance of
ciphertext multiplications, the most demanding arithmetic FHE operation, by
accelerating several primitive operations on polynomials, such as polynomial
additions and subtractions, Hadamard product, and Number Theoretic Transform.
CoFHEE supports polynomial degrees of up to n=214 with a maximum
coefficient sizes of 128 bits, while it is capable of performing ciphertext
multiplications entirely on chip for n≤213. CoFHEE is fabricated in
55nm CMOS technology and achieves 250 MHz with our custom-built low-power
digital PLL design. In addition, our chip includes two communication interfaces
to the host machine: UART and SPI. This manuscript presents all steps and
design techniques in the ASIC development process, ranging from RTL design to
fabrication and validation. We evaluate our chip with performance and power
experiments and compare it against state-of-the-art software implementations
and other ASIC designs. Developed RTL files are available in an open-source
repository