An symmetric encryption scheme with dynamic key based on obfuscation of point functions with multibit output(MBPF)is presented.A MBPF obfuscator with fully-entropic security

implying virtual black-box property(VBB)

can be used to construct semantically secure encryption schemes with wrong key detection for

α(n-

weak keys. The symmetric encryption scheme is just the fully-entropic security MBPF obfuscator

whose key is deduced by a sensitive function . The sensitive function with two inputs

one is a secret key and another is a random key

and thus output key is random. The symmetric encryption scheme is more secure and implement simple.