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We show that two well-known and widely employed publickey encryption schemes-RSA Optimal Asymmetric Encryption Padding (RSA-OAEP) and Diffie-Hellman Integrated Encryption Standard (DHIES), the latter one instantiated with a one-time pad,-are secure under (the strong, simulation-based security notion of) selective opening security against chosen-ciphertext attacks in the random oracle model. Both schemes are obtained via known generic transformations that transform relatively weak primitives (with security in the sense of one-wayness) to INDCCA secure encryption schemes. We prove that selective opening security comes for free in these two transformations. Both DHIES and RSA-OAEP are important building blocks in several standards for public key encryption and key exchange protocols. They are the first practical cryptosystems that meet the strong notion of simulation-based selective opening (SIM-SO-CCA) security.

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We show that two well-known and widely employed public-key encryption schemes-RSA Optimal Asymmetric Encryption Padding (RSA-OAEP) and Diffie-Hellman Integrated Encryption Scheme (DHIES), instantiated with a one-time pad,-are secure under (the strong, simulation-based security notion of) selective opening security against chosen-ciphertext attacks in the random oracle model. Both schemes are obtained via known generic transformations that transform relatively weak primitives (with security in the sense of one-wayness) to IND-CCA secure encryption schemes. We also show a similar result for the well-known Fujisaki-Okamoto transformation that can generically turn a one-way secure public key encryption system and a one-time pad into a INDCCA-secure public-key encryption system. We prove that selective opening security comes for free in these transformations. Both DHIES and RSA-OAEP are important building blocks in several standards for public key encryption and key exchange protocols. The Fujisaki-Okamoto transformation is very versatile and has successfully been utilised to build efficient lattice-based cryptosystems. The considered schemes are the first practical cryptosystems that meet the strong notion of simulation-based selective opening (SIM-SO-CCA) security.