side channel discussion

cryptography/aes-cbc-poa/DESCRIPTION.md

@@ -32,3 +32,4 @@ For the first block, this is the IV, but not for the rest!
 **FUN FACT:**
 The only way to prevent a Padding Oracle Attack is to avoid having a Padding Oracle.
 Depending on the application, this can be surprisingly tricky: a failure state is hard to mask completely from the user/attacker of the application, and for some applications, the padding failure is the only source of an error state!
+Moreover, even if the error itself is hidden from the user/attacker, it's often _inferrable_ indirectly (e.g., by detecting timing differences between the padding error and padding success cases).