中文摘要：

文章首先改进了一个小公钥的RSA加密方案。然后，基于RSA签名算法，设计了一个双方不可否认的小公钥RSA加密协议。在这个协议中，发送方只需对发送消息进行一次密文签发。通过服务器。掇文可安全地发送给任意有限个接收者。该协议具有发送和接收双方都不能抵赖的性质。最后，探讨了该协议的实际应用。

英文摘要：

In the first of the paper, we have improved a RSA scheme with small public key. Then, based on the RSA digital signature algorithm, we design an undeniable RSA encryption protocol with small public key for both sides. In the protocol, the sender only needs to sign the encrypted message by one time. Server will give messages to any limited receivers safely. Finally, its application in practical affairs is discussed.