X-Git-Url: https://git.distorted.org.uk/~mdw/doc/ips/blobdiff_plain/41761fdc7bb8f1ed87f5e1116d389158513ee280..b912aadfc4eb26f1c4cf3332eb510b41a4d9a036:/enc-ies.tex diff --git a/enc-ies.tex b/enc-ies.tex index cd0f5c6..3f53936 100644 --- a/enc-ies.tex +++ b/enc-ies.tex @@ -1,9 +1,10 @@ \xcalways\section{Integrated public-key encryption schemes}\x The formulation here is original work by the author. I've tried to -generalize the work by (among others), Shoup, and Abdalla, Bellare and -Rogaway. The final proof is from a Usenet article prompted by David -Hopwood, but based on the DHAES proof by ABR. +generalize the work by (among others), Shoup \cite{Shoup:2001:PIS}, and +Abdalla, Bellare and Rogaway \cite{Abdalla:2001:DHIES}. The final proof is +from a Usenet article prompted by David Hopwood, but based on the DHIES proof +in \cite{Abdalla:2001:DHIES}. \xcalways\subsection{Introduction and definitions}\x @@ -28,9 +29,9 @@ Hopwood, but based on the DHAES proof by ABR. \head{An obvious approach} A simple approach would be to generate a random key for some secure (i.e., - IND-CCA) symmetric scheme, encrypt the message under that key, and, encrypt - the key under the recipient's public key (using some IND-CCA2 public-key - scheme). + IND-CCA2) symmetric scheme, encrypt the message under that key, and, + encrypt the key under the recipient's public key (using some IND-CCA2 + public-key scheme). This is obviously secure. But the security results for most public-key schemes are less than encouraging: the reductions, even for OAEP+, are @@ -133,8 +134,8 @@ Hopwood, but based on the DHAES proof by ABR. \[ \Pr[S] = \frac{\Adv{ohd}{\Xid{\mathcal{K}}{OWF}^{\mathcal{T}, H}}(A)}{2} + \frac{1}{2}. \]% - Let $F$ be the event that $A$ queries $H$ at $x^*$. Then by Shoup's Lemma - (lemma~\ref{lem:shoup}, page~\pageref{lem:shoup}), + Let $F$ be the event that $A$ queries $H$ at $x^*$. Then by + Lemma~\ref{lem:shoup} (slide~\pageref{lem:shoup}), \[ \left|\Pr[S] - \frac{1}{2}\right| \le \Pr[F]. \] Now consider this adversary $I$, attempting to invert the one-way function. @@ -321,7 +322,7 @@ Hopwood, but based on the DHAES proof by ABR. \InSec{ind-cca2}(\Xid{G}{IES}^{\mathcal{K}, \mathcal{E}}; t, q_D) \\ & \le 2 \cdot \InSec{ohd}(\mathcal{K}; t + O(q_D), q_D) + - \InSec{ftg-cca}(\mathcal{E}; t + O(q_D), 0, q_D). + \InSec{ftg-cca2}(\mathcal{E}; t + O(q_D), 0, q_D). \end{eqnarray*} Note how weak the security requirements on the encryption scheme are: no chosen-plaintext queries are permitted! @@ -348,7 +349,7 @@ Hopwood, but based on the DHAES proof by ABR. simulation of $A$'s attack game, and hence wins with probability \[ \frac{\Adv{ind-cca2}{\Xid{G}{IES}^{\mathcal{K}, \mathcal{E}}}}{2} + \frac{1}{2}. \]% - We construct a new adversary $C$, attacking $\mathcal{E}$ in the FTG-CCA + We construct a new adversary $C$, attacking $\mathcal{E}$ in the FTG-CCA2 sense, to help us bound $B$'s probability of success when $h$ is chosen randomly. \begin{program}