We show that unless a cryptanalyst can completely break the RSA encryption, any heuristic oracle he uses to determine the least significant bit of the cleartext must have an error probability greater than 1/ 2-ε. 证明了,对于任意用于确定RSA明文的最后一个有效位的启示,必须有大于1/2-ε的出错概率,否则密码分析人员能够完全破译RSA。