Notice
2.4. Notions of Security
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Descriptif
In this session, we will study thenotion of security of public-key scheme. A public-key scheme isone-way if the probability of success of any adversaryrunning in polynomial time is negligible. That is,without the private key, it is computationally impossibleto recover the plaintext. For the McEliece, if weassume that the general decoding problem of a linear codeis on average a difficult problem and there exists noefficient distinguisher for Goppa codes, then the McEliecescheme has the One-Wayness property. However, McEliece isvulnerable to many attacks as we will see in the followingslides, and also in the next session. In this session, we will usethe notion of Oracle, along the following slides. An Oracle is simply a system thattakes queries and provides answers. The queries might beplaintext or ciphertext and the answers are thecorresponding ciphertext or plaintext. Non-malleabilityguarantees that it is infeasible to modify the ciphertext intoanother ciphertext of related messages. The following attack tellsus that the McEliece does not satisfy non-malleability.Suppose that the adversary intercepts a ciphertext.That is, the ciphertext is the sum of an encodedmessage and a random error. Then, the adversary canchoose a codeword and generate a new ciphertext withoutknowing the original plaintext. And there exists a relationbetween the first plaintext and the new plaintext.Now, suppose that the adversary has accessto a decryption Oracle.
Intervention
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