Weak adaptive chosen ciphertext secure hybrid encryption scheme

We propose a security notion named as weak adaptive chosen ciphertext security(INDWCCA) for hybrid encryption schemes. Although it is weaker than adaptive chosen ciphertext security(INDCCA), a IND-WCCA secure hybrid encryption scheme can be used in any situations that a IND-CCA secure hybrid encryption scheme used in. We show that IND-WCCA secure hybrid encryption scheme can be constructed from IND-CCA secure KEM and IND-PA secure DEM. Since IND-PA is the basic requirement of symmetric key encryption schemes, IND-WCCA hybrid encryption scheme is very flexible and can use most of the stream ciphers and block ciphers as the DEM part of the scheme. Use the new secure notion we can refine current IND-CCA secure hybrid encryption schemes and get more efficient IND-WCCA secure hybrid encryption schemes.