Possible Duplicate:
CPA Secure Chosen plaintext scheme
The example for IND-CPA secure schemes given is generally:
for a random r,
$Enc_k(m) =(r|| E_k(r)$ $XOR$ $m)$ where $E$ is a $PRF$
But does the role of r and k really matter--i.e. isn't this equally secure?
$Enc_k(m) =(r|| E_r(k)$ $XOR$ $m)$ ?
