diff --git a/GSoCIdeas2010.md b/GSoCIdeas2010.md
index e710704..208d156 100644
--- a/GSoCIdeas2010.md
+++ b/GSoCIdeas2010.md
@@ -33,7 +33,7 @@ Students:  you don't have to use one of the following Ideas.  You can come up wi
      * Special scheme handling in browser add-ons
    * [CAJA](http://code.google.com/p/google-caja) approach: Require all Javascript to pass the CAJA verifier in the Tahoe web frontend, then create an interface to the tahoe webapi which matches the intended capability semantics.
  * Tahoe Cryptography:
-   * Help us author a paper proving the security of the "Semi-Private Keys" construction from <http://allmydata.org/~zooko/lafs.pdf> .  Implement small, secure Tahoe capabilities based on Semi-Private Keys.
+   * Help us author a paper proving the security of the "Semi-Private Keys" construction from <http://allmydata.org/~zooko/lafs.pdf> .  Implement small, secure Tahoe capabilities based on Semi-Private Keys. #217
 
 ## Building Things On Top Of Tahoe
  * an interactive tree browser web frontend in JavaScript (Nathan has written most of one -- what can it grow into?)