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In the case of chosen ciphertext attack, we are considering a more powerful adversary, where the adversary can make a query to an oracle O
In the case of chosen ciphertext attack, we are considering a more powerful adversary, where the adversary can make a query to an oracle O which takes a ciphertext as input and outputs the corresponding plaintext. For instance, let Enc(:,-) be an encryption scheme, and for any message m, we write cm = Enc(sk, m) to be the corresponding ciphertext. Then the adversary can upload Cm to the oracle O and the oracle will give back m to the adversary. Please design a chosen ciphertext attack for the following scheme: Enc(:,.) is an encryption scheme; there exists an efficient and publicly known algorithm S such that, for any message m S(Enc(sk, m)) = Enc(sk, m + 1). The adversary wants to corrupt a ciphertext c*, but it is not allowed to upload c* to the oracle directly. In the case of chosen ciphertext attack, we are considering a more powerful adversary, where the adversary can make a query to an oracle O which takes a ciphertext as input and outputs the corresponding plaintext. For instance, let Enc(:,-) be an encryption scheme, and for any message m, we write cm = Enc(sk, m) to be the corresponding ciphertext. Then the adversary can upload Cm to the oracle O and the oracle will give back m to the adversary. Please design a chosen ciphertext attack for the following scheme: Enc(:,.) is an encryption scheme; there exists an efficient and publicly known algorithm S such that, for any message m S(Enc(sk, m)) = Enc(sk, m + 1). The adversary wants to corrupt a ciphertext c*, but it is not allowed to upload c* to the oracle directly
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