In this paper, we formally prove that padding the plaintext with a random bit-string provides the semantic security against chosen plaintext attack (IND-CPA) for the McEliece (and its dual, the Niederreiter) cryptosystems under the standard assumptions. Such padding has recently been used by Suzuki, Kobara and Imai in the context of RFID security. Our proof relies on the technical result by Katz and Shin from Eurocrypt '05 showing "pseudorandomness" implied by the learning parity with noise (LPN) problem. We do not need the random oracles as opposed to the known generic constructions which, on the other hand, provide a stronger protection as compared to our scheme-against (adaptive) chosen ciphertext attack, i.e., . In order to show that the padded version of the cryptosystem remains practical, we provide some estimates for suitable key sizes together with corresponding workload required for successful attack.

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Abstract-Information-theoretically secure string oblivious transfer (OT) can be constructed based on discrete memoryless channel (DMC). The oblivious transfer capacity of a channel characterizes -similarly to the (standard) information capacity -how efficiently it can be exploited for secure oblivious transfer of strings. The OT capacity of a Generalized Erasure Channel (GEC) -which is a combination of a (general) DMC with the erasure channel -has been established by Ahlswede and Csizar at ISIT'07 in the case of passive adversaries. In this paper, we present the protocol that achieves this capacity against malicious adversaries for GEC with erasure probability at least 1/2. Our construction is based on the protocol of Crépeau and Savvides from Eurocrypt'06 which uses interactive hashing (IH). We solve an open question posed by the above paper, by basing it upon a constant round IH scheme (previously proposed by Ding et al at TCC'04). As a side result, we show that Ding et al IH protocol can deal with transmission errors.