# Tag Info

4

Can a variable that is not explicitly computed correlate with the power consumption? Yes, and this can happen in several ways. When you say "not computed explicitly", I assume you mean that the computation is performed on a masked value or share instead. That is, the secret inputs (referred to as the key by the paper you link to) themselves do not ...

4

You can (and should) do the reduction in constant time using masking. That is, instead of using the following (non-bitsliced) pseudo-C code to do the reduction: if ((result >> 8) & 1) { /* bit 8 is set: clear it and flip bits 0, 1, 3 and 4 */ result ^= 0x11b; } you can simply do: result ^= 0x11b * ((result >> 8) & 1); ...

1

The main advantage I have heard is reducing the amount of data the client has to send to the cloud. As said in A Comparison of the Homomorphic Encryption Schemes FV and YASHE: [...] ciphertext expansion (i.e. the ciphertext size divided by the plaintext size) of current FHE schemes is prohibitive (thousands to millions). For example using ...

1

Most of side channel attacks are depends on algorithm and implementation. In several cases, power consumption is evidently visible in algorithm. For example in the algorithm for elliptic curve points multiplication, for computing $Q=k\cdot P$ we have following algorithm: Let $k$ be $l$ bit. Q=P for i from l-1 to 0 do Q = 2Q if k_i == 1 then Q = Q+P ...

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