The McEliece public key cryptosystem (PKC) is regarded as secure in the presence of quantum computers because no efficient quantum algorithm is known for the underlying problems, which this cryptosystem is built upon. As we show in this paper, a straightforward implementation of this system may feature several side channels. Specifically, we present a Timing Attack which was executed successfully against a software implementation of the McEliece PKC. Furthermore, the critical system components for key generation and decryption are inspected to identify channels enabling power and cache attacks. Implementation aspects are proposed as countermeasures to face these attacks.

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Abstract. In this work we present the first practical key-aimed timing attack against code-based cryptosystems. It arises from vulnerabilities that are present in the inversion of the error syndrome through the Extended Euclidean Algorithm that is part of the decryption operation of these schemes. Three types of timing vulnerabilities are combined to a successful attack. Each is used to gain information about the secret support, which is part of code-based decryption keys: The first allows recovery of the zero-element, the second is a refinement of a previously described vulnerability yielding linear equations, and the third enables to retrieve cubic equations.

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