该程序使用RSA公钥算法实现了对一个字符串的加密和解密功能。其中，采用欧几里德算法（即辗转相除法）来判断两个数是否是素数。另外，使用菜单选项来选择当前是要“加密”还是“解密”。-The program use RSA public key algorithm is presented for a string of encryption and decryption function. Among them, the Euclidean algorithm (namely division algorithm) to determine whether the number of two prime Numbers. In addition, the use of the menu options to choose the current is to "encryption or decryption".