# Is AES-CTR-NoPadding resistant to variable-length chosen-plaintext attack?

Consider the following scenario: an adversary $A$ with access to an encryption oracle $\mathcal{O}$ is able to choose $n \in \mathbb{N}$ and pick $p_1,\dots,p_n$ such that $\forall i \in \{1,\dots,n\}:$ $A$ queries $\mathcal{O}$ with $p_i$ in order to obtain ciphertext $c_i := \texttt{AES_CTR_ENC}(p_i,k,IV)$ for some unkown key $k$ and initialization vector $IV$ (n padding scheme). Furthermore, assume that $|p_i| \neq |p_j|$ $\forall i\neq j$.

Is it possible that the abovementioned encryption scheme (AES-CTR without padding) is somehow resistant to this type of attack?

• I assume you mean AES_CTR_ENC under a single key $k$, but how many $IV$s are there in the game? – DannyNiu Nov 1 '17 at 11:15
• @DannyNiu you can assume that the pair (k,IV) does not ever repeat. – Ricardo Miranda Nov 1 '17 at 11:47