维吉尼亚加密与解密

 /// <summary>
    /// 维吉尼亚加密与解密
    /// </summary>
    public static class VigenereHelper
    {
        /// <summary>
        /// 密钥
        /// </summary>
        private static string TableKey = @"abcdefghijklmnopqrstuvwxyz_ABCDEFGHIJKLMNOPQRSTUVWXYZ-0123456789=&";

        /// <summary>
        /// 生成密钥字符串
        /// </summary> 
        /// <param name="input">明文或者密文</param>
        /// <returns></returns>
        private static string GetKey(string input)
        {
            string key = "ZoveCenter202104091148";
            StringBuilder sbKey = new StringBuilder(key);
            //如果密钥长度比str短，则以不断重复密钥的方式生成密钥字符串
            while (sbKey.Length < input.Length)
            {
                sbKey.Append(key);
            }
            return sbKey.ToString();
        }

        /// <summary>  
        /// 加密算法  
        /// </summary>  
        /// <param name="input">明文字符串</param>   
        /// <returns>字符串</returns>  
        public static string Encrypt(string input)
        {
            //密钥字符串
            string K = GetKey(input);
            StringBuilder sbRel = new StringBuilder();
            for (var loop = 0; loop < input.Length; loop++)
            {
                //明文字符位置
                var iP = TableKey.IndexOf(input[loop]);
                if (iP == -1)
                {
                    sbRel.Append(input[loop]);
                }
                else
                {
                    //密钥字符位置
                    var iK = TableKey.IndexOf(K[loop]);
                    if (iK == -1)
                    {
                        throw new Exception("密钥中包含非法字符：" + TableKey[loop]);
                    }
                    sbRel.Append(TableKey[(iP + iK) % TableKey.Length]);
                }
            }
            return sbRel.ToString();
        }

        /// <summary>  
        /// 解密  
        /// </summary>  
        /// <param name="input">密文</param>   
        /// <returns>返回解密后的字符串</returns>  
        public static string Decrypt(string input)
        {
            //密钥字符串
            string K = GetKey(input);
            StringBuilder sbRel = new StringBuilder();
            for (var loop = 0; loop < input.Length; loop++)
            {
                //密钥判断
                var iK = TableKey.IndexOf(K[loop]);
                //密文字符
                var iC = TableKey.IndexOf(input[loop]);
                if (iC == -1)
                {
                    sbRel.Append(input[loop]);
                }
                else if (iK > iC)
                {
                    sbRel.Append(TableKey[iC + TableKey.Length - iK]);
                }
                else
                {
                    sbRel.Append(TableKey[iC - iK]);
                }
            }
            return sbRel.ToString();
        }
    }