A tale of two shares: why two-share threshold implementation seems worthwhile—and why it is not

Cong Chen, Thomas Eisenbarth

Abstract: This work explores the possibilities for practical Threshold Implementation (TI) with only two shares in order for a smaller design that needs less randomness but is still first-order leakage resistant. We present the first two-share Threshold Implementations of two lightweight block ciphers—Simon and Present. The implementation results show that two-share TI improves the compactness but usually further reduces the throughput when compared with first-order resistant three-share schemes. Our leakage analysis shows that two-share TI can retain perfect first-order resistance. However, the analysis also exposes a strong second-order leakage. All results are backed up by simulation as well as analysis of actual implementations.