I thought of this recently:
An attacker can observe the lengths and timing of requests made over an HTTPS connection. Given this, can an attacker reliably deduce which page a victim visits despite the connection being "secure"?
I know there is some message padding to integer multiples of a certain length; however, could the lengths of enough messages be combined to give a good guess as to which pages the victim visits? Also, has there been any work done on this or a similar attack?
Here's an example:
Website A has 3 public pages with the following sizes:
A1 100 bytes - embarrassing A2 200 bytes A3 100 bytes
Let's assume that A1 and A2 reference an external resource with size 300 bytes.
If an attacker observes a response with length 100, she knows the victim has requested either page A1 or A3. Then, if she observes a response of length 300, then she can deduce that the victim has visited page A1.