Shamir和Schorr对Rabin数字签名方案提出一种有效的攻击方法 ,称为Shamir攻击 .为了避免Shamir攻击 ,本文提出一种有效的比特位扰乱法 (BitPerturbation) .基于Rabin公钥密码体制 ,Harn和Kiesler提出一种改进的公钥密码体制、数字签名方案和认证加密方案 .本文指出Harn和Kiesler提出的密码体制是不安全的 ,并设计一种安全的数字签名方案 Shamir and Schorr propose an effective attack method for Rabin digital signature scheme called Shamir attack.In order to avoid Shamir attack, this paper proposes an effective Bit Perturbation method based on Rabin public key cryptosystem, Harn and Kiesler This paper proposes an improved public key cryptosystem, digital signature scheme and authentication scheme.This paper points out that the cryptosystem proposed by Harn and Kiesler is not secure, and designs a secure digital signature scheme