# Chosen Plaintext Attacks against an Affine Cipher

Assuming the ability to launch Chosen Plaintext Attacks (CPA), how many oracle calls an attacker needs to break the affine cipher? and how

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What happens if the attacker asks the oracle to encrypt $x = 0$? –  Thomas Feb 25 '13 at 9:13

The answer is 1 I think because if we apply a chosen plain text attack, then we need at least 2 encrypted alphabets and two plaintext alphabets corresponding to the related encrypted alphabets. Then we will have two variable and two equations.