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diff --git a/doc/paper/trash b/doc/paper/trash deleted file mode 100644 index ced86833a..000000000 --- a/doc/paper/trash +++ /dev/null @@ -1,90 +0,0 @@ - - - -\begin{proposition} -If there are no refresh operations, then any adversary who links -coins can recognize blinding factors. -\end{proposition} - -\begin{proof} -In effect, coin withdrawal transcripts consist of numbers $b m^d \mod n$ - -The blinding factor is created with a full domain hash -\end{proof} - - -We say a blind signature -linkable if some probabilistic polynomial -time (PPT) adversary has a non-negligible advantage indentifying -the - - -, given some withdrawal and refresh -transcripts - - - - - -We say a coin $C_0$ is {\em linkable} to the withdrawal or refresh -operation in which it was created if some probabilistic polynomial -time (PPT) adversary has a non-negligible advantage in guessing -which of $\{ C_0, C_1 \}$ were created in that operation, - where $C_1$ is an unrelated third coin. - -% TODO: Compare this definition with some from the literature -% TODO: Should this definition be broadened? - -.. reference literate about withdrawal .. - -\begin{proposition} -In the random oracle model, -if a coin created by refresh is linkable to the refresh operation -that created it, then some PPT adversary has a non-negligible -advantage in determining the shared secret of an eliptic curve -Diffie-Hellman key exchange on curve25519. -\end{proposition} - -% Intuitively this follows from \cite{Rudich88}[Theorem 4.1], but -% we provide slightly more formality. - -\begin{proof} -Assume a PPT adversary $A$ has a non-negligible advantage in solving -the linking problem. - -We have two curve points $C = c G$ and $T = t G$ for which -we wish to compute the shared secret $c t G$. - -We make $C$ into a coin by singing it with a denomination key -invented for this purpose. We let $T^{(1)}$ denote $T$ and -invent $\kappa-1$ linking keys $T^{(2)},\ldots,T^{(\kappa)}$. - -We shall extract the shared secret by constructing an algorithm -that runs the refresh protocol and then runs $A$ using the natural -simulation of a random oracle, namely answering new queries with -random bits, yet recording the answers in a database so as to -provide idendical answers to identical queries. - -We may take $\gamma=1$ by restarting the exchange with a clean -database. As a result, the exchange never checks the commitment -covering $T^{(1)}$, but this alone does not suffice to discount -the any information contained in the commitment. - -Instead, we observe that our commitments consist of random oracle -queries distinct from anything else in the protocol, so they contain -no information of use to $A$, and can safely be omitted. - -We do not know $c t G$ so our simulation cannot run the KDF to -derive the new coin that $A$ can link. - - -... random oracle .. -\end{proof} - -In principle, one might worry if coins created in the same withdrawal -or refresh opeartion might be linkable to one another without being -linkable to the operation, but addressing this concern would take us -somewhat far afield and require similar methods. - - - |