# Tag Info

Consider a four-block message $P_1 \mathbin\| P_2 \mathbin\| P_3 \mathbin\| P_4$. The corresponding ciphertext under initialization vector $\mathit{IV}$ is $C_1 \mathbin\| C_2 \mathbin\| C_3 \mathbin\| C_4$, where: \begin{equation*}\newcommand{\diff}[1]{\color{red}{#1}} \begin{matrix} &&P_1 &&\diff{P_2} &&P_3 &&...
Encryption process in CBC mode is performed as \begin{align} C_1 &= Enc_k(P_1 \oplus IV)\\ C_i &= Enc_k(P_i \oplus C_{i-1}),\;\; 1 < i \leq nb, \end{align} where $nb$ is the number of blocks. CBC is designed for chaining, therefore while encryption, if there is one block error at position $i$, it will affect the rest of ciphertext. This also can ...