This is from a previous exam question and I'm not really sure how to approach this properly
We're using a block-cipher mode that encrypts
$C_i$ = $E_k$ ($P_i$ $\oplus$ $C_{i-1}$ $\oplus$ $P_{i-1}$) with $C_0$ = IV and $P_0$ = 0.
Indicate whether information leaks on the plaintext if too many plaintext blocks are encrypted under the same key (use as example DES).
Now I'm not really sure how to indicate this. But I assumed that if the IV is truly random that no leakage should happen.
My opinion even if you do a chosen-plaintext attack where $P_1$ = 0
$C_1$ = $E_k$ ($P_1$ $\oplus$ $IV$ $\oplus$ $P_0$) = $E_k$ ($0$ $\oplus$ $IV$ $\oplus$ $0$) which would give $C_1$ = $E_k$ ($IV$)
$C_2$ = $E_k$ ($P_2$ $\oplus$ $C_1$ $\oplus$ $P_1$) = $E_k$ ($P_2$ $\oplus$ $E_k$ ($IV$) $\oplus$ $0$)
$...$
I don't see how it would leak any information on the plaintext. I might be assessing the question wrong though.