Tag-KEM from Set Partial Domain One-Way Permutations

Recently a framework called Tag-KEM/DEM was introduced to construct efficient hybrid encryption schemes. Although it is known that generic encode-then-encrypt construction of chosen ciphertext secure public-key encryption also applies to secure Tag-KEM construction and some known encoding method like OAEP can be used for this purpose, it is worth pursuing more efficient encoding method dedicated for Tag-KEM construction. This paper proposes an encoding method that yields efficient Tag-KEM schemes when combined with set partial one-way functions such as RSA and Rabin's encryption scheme. We also present an efficient Tag-KEM which is CCA-secure under general factoring assumption rather than Blum factoring assumption.