diff --git a/exam/ex.tex b/exam/ex.tex
index 45bacfd..8e88781 100644
--- a/exam/ex.tex
+++ b/exam/ex.tex
@@ -186,7 +186,12 @@
     \item IND-CCA2 is proven for both the KEM and the PKC. IND-CPA is proven for
       the KEM.
 
-    \item \TODO
+    \item LEDAcrypt is based on the hardness of the decoding problem for linear
+      codes. Given a parity-check matrix $H$ and a received codeword $y$, the
+      syndrome is $s=yH$. Find a minimum-weight solution $z_0$ for the equation
+      $s=zH$. The best estimate for the received codeword is $x=y+z_0$. Finding
+      a minimum-weight solution to $s=zH$ given $s$ and $H$ is
+      $\mathsf{NP}$-hard.
 
     \item \TODO