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TomCN0803 avatar Crypto

Find the product of two sums via SMPC

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TomCN0803

I'm currently working on a distributed threshold DSA scheme that requires to find the product of two sums via secure multi-party computation. Specifically speaking, every one of $n$ parties $P_i$ possesses a DSA key pair $(sk_i, pk_i)$, where $sk_i=d_i \in \mathbb{Z}_q$ and $pk_i = g^{d_i}$. I want to collectively generate a signature $S_{\Sigma} = k_{\Sigma}^{-1}(m+r_{\Sigma}d_{\Sigma})$, where$k_{\Sigma}=k_1+\dots k_n$, $r_{\Sigma}d_{\Sigma}=(r_1+\dots+r_n)\cdot(d_1+\dots+d_n)$. My prior question is that is there a proper paradigm to compute $r_{\Sigma}d_{\Sigma}$ without leaking information about secret keys $(d_1,\dots,d_n)$? For computing $k_{\Sigma}$, I'm using the BGW Protocol and Shamir threshold secret sharing scheme. Is it possible to compute $r_{\Sigma}d_{\Sigma}$ using BGW protocol as well?

PS: I'm new to SMPC, and English is not my first language. Sorry for the troubles. Thanks!

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alexander
If you are going to compute the product of two secret numbers (in your case r*d), then, you can use Beaver's multiplication triple to do it.
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Mark avatar Crypto
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Mark

Yes it is, see for example this page. Note that multiplication requires $O(n^2)$ additional communication, in contrast to addition (which is free).

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