c# 加密 解密函数， 加密 解密 算法，自定义密钥

/// <summary>
/// 利用DES加密算法加密字符串（可解密）
/// </summary>
/// <param name="plaintext">被加密的字符串</param>
/// <param name="key">密钥（只支持8个字节的密钥）</param>
/// <returns>加密后的字符串</returns>
private static string EncryptString(string plaintext, string key)
{
//访问数据加密标准(DES)算法的加密服务提供程序 (CSP) 版本的包装对象
DESCryptoServiceProvider des = new DESCryptoServiceProvider();
des.Key = ASCIIEncoding.ASCII.GetBytes(key);　//建立加密对象的密钥和偏移量
des.IV = ASCIIEncoding.ASCII.GetBytes(key);　 //原文使用ASCIIEncoding.ASCII方法的GetBytes方法

byte[] inputByteArray = Encoding.Default.GetBytes(plaintext);//把字符串放到byte数组中

MemoryStream ms = new MemoryStream();//创建其支持存储区为内存的流　
//定义将数据流链接到加密转换的流
CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(), CryptoStreamMode.Write);
cs.Write(inputByteArray, 0, inputByteArray.Length);
cs.FlushFinalBlock();
//上面已经完成了把加密后的结果放到内存中去
StringBuilder ret = new StringBuilder();
foreach (byte b in ms.ToArray())
{
ret.AppendFormat("{0:X2}", b);
}
ret.ToString();
return ret.ToString();
}
/// <summary>
/// 利用DES解密算法解密密文（可解密）
/// </summary>
/// <param name="ciphertext">被解密的字符串</param>
/// <param name="key">密钥（只支持8个字节的密钥，同前面的加密密钥相同）</param>
/// <returns>返回被解密的字符串</returns>
private static string DecryptString(string ciphertext, string key)
{
try
{
DESCryptoServiceProvider des = new DESCryptoServiceProvider();

byte[] inputByteArray = new byte[ciphertext.Length / 2];
for (int x = 0; x < ciphertext.Length / 2; x++)
{
int i = (Convert.ToInt32(ciphertext.Substring(x * 2, 2), 16));
inputByteArray[x] = (byte)i;
}

des.Key = ASCIIEncoding.ASCII.GetBytes(key);　//建立加密对象的密钥和偏移量，此值重要，不能修改
des.IV = ASCIIEncoding.ASCII.GetBytes(key);
MemoryStream ms = new MemoryStream();
CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(), CryptoStreamMode.Write);

cs.Write(inputByteArray, 0, inputByteArray.Length);

cs.FlushFinalBlock();

//建立StringBuild对象，createDecrypt使用的是流对象，必须把解密后的文本变成流对象
StringBuilder ret = new StringBuilder();

return System.Text.Encoding.Default.GetString(ms.ToArray());
}
catch (Exception)
{
return "error";
}
}