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diff --git a/ACSAC/proofs/proof_advdebias.tex b/ACSAC/proofs/proof_advdebias.tex new file mode 100644 index 0000000..06212a0 --- /dev/null +++ b/ACSAC/proofs/proof_advdebias.tex @@ -0,0 +1,30 @@ +Definition~\ref{def:dp} of \dempar can be written synthetically as the following property: +$P_{\hat{Y},S}=P_{\hat{Y}}\otimes P_{S}$. +Where $P_{\hat{Y}}\otimes P_{S}$ is the product measure defined as the unique measure on +$\mathcal{P}(\mathcal{Y})\times\mathcal{P}(\mathcal{S})$ such that +$\forall y\in\mathcal{P}(\mathcal{Y})\forall s\in\mathcal{P}(\mathcal{S})\quad P_{\hat{Y}}\otimes P_{S}(y\times s) = P_{\hat{Y}}(y)P_{S}(s)$. +This is equivalent to definition~\ref{def:dp} for binary labels and sensitive attribute but more general because when $\hat{Y}$ is not binary as in soft labels, this new definition is well defined. +% We write formally +\begin{definition} +\label{def:dps} + $\hat{Y}$ satisfies extended \dempar for $S$ if and only if: $P_{\hat{Y},S}=P_{\hat{Y}}\otimes P_{S}$. +\end{definition} +This definition is the same as the statistical parity introduced for fair regression~\cite{fairreg}. +Note that we can not derive a quantity similar to \demparlevel with this definition but this extended \dempar assures indistinguishably of the sensitive attribute when looking at the soft labels. +We have the following theorem: +\begin{theorem}\label{th:advdebias} + The following propositions are equivalent: ``$\hat{Y}_s$ is independent of $S$'' and ``Balanced accuracy of \aia in \ref{tm:soft} is $\frac{1}{2}$'' +\end{theorem} +\begin{proof} +Let's show that it is equivalent to say "all attack models have a balanced accuracy of 0.5" and "the target model satisfies extended demographic parity". +{\footnotesize + \begin{align*} + &\forall a~P(\hat{Y}\in a^{-1}(\{0\})|S=0)+P(\hat{Y}\in a^{-1}(\{1\})|S=1) = 1\\ + \Leftrightarrow&\forall a~P(\hat{Y}\in a^{-1}(\{0\})|S=0)=P(\hat{Y}\in a^{-1}(\{0\})|S=1)\\ + \Leftrightarrow&\forall A~P(\hat{Y}\in A)|S=0)=P(\hat{Y}\in A|S=1) \\ + \Leftrightarrow &P_{\hat{Y},S}=P_{\hat{Y}}\otimes P_{S} + \end{align*} + } +\end{proof} + +%In conclusion, with extended \dempar we can not unconditionally bound the balanced accuracy of the attack without introducing distances in the space of distributions, but it gives us a condition to protect the sensitive attribute in case of an adversary gaining access to soft labels (AS).
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