1231 \item cryptography is often not {\bf the} answer\bigskip\bigskip  

  1230 \item cryptography is often not the problem\bigskip\bigskip  

  1232 \end{itemize}

  1231 \end{itemize}

  1233 

  1232 

  1234 \end{frame}

  1233 \end{frame}

  1235 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

  1234 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

  1236 

  1235 

  1237 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

  1238 \begin{frame}[c]

  1239 \frametitle{Best Practices}

  1240 

  1241 {\bf Principle 1:} Every message should say what it means: the interpretation of 

  1242 a message should not depend on the context.\bigskip\pause

  1243 

  1244 {\bf Principle 2:} If the identity of a principal is essential to the meaning of a message, it is prudent 

  1245 to mention the principal’s name explicitly in the message (though difficult).\bigskip

  1246 

  1247 \end{frame}

  1248 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

  1249 

  1250 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

  1251 \begin{frame}[c]

  1252 

  1253 {\bf Principle 3:} Be clear about why encryption is being

  1254 done. Encryption is not cheap, and not asking precisely why it is

  1255 being done can lead to redundancy. Encryption is not synonymous with

  1256 security.

  1257 

  1258 \begin{center}

  1259 Possible Uses of Encryption

  1260 

  1261 \begin{itemize}

  1262 \item Preservation of confidentiality: \bl{$\{X\}_K$} only those that have \bl{$K$} may recover \bl{$X$}.

  1263 \item Guarantee authenticity: The partner is indeed some particular principal.

  1264 \item Guarantee confidentiality and authenticity: binds two parts of a message --- 

  1265 \bl{$\{X,Y\}_K$} is not the same as \bl{$\{X\}_K$} and \bl{$\{Y\}_K$}.

  1266 \end{itemize}

  1267 \end{center}

  1268 

  1269 \end{frame}

  1270 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

  1271 

  1272 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

  1273 \begin{frame}[c]

  1274 \frametitle{Best Practices}

  1275 

  1276 {\bf Principle 4:} The protocol designer should know which trust relations his protocol depends on, and why the dependence is necessary. The reasons for particular trust relations being acceptable should be explicit though they will be founded on judgment and policy rather than on logic.\bigskip

  1277 

  1278 

  1279 Example Certification Authorities: CAs are trusted to certify a key only after proper steps 

  1280 have been taken to identify the principal that owns it.

  1281 

  1282 \end{frame}

  1283 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%