加密，解密 自定义密钥

/// <summary>
/// 加密
/// </summary>
/// <param name="pToEncrypt"></param>
/// <param name="sKey">密钥必须是8位</param>
/// <returns></returns>
public static string MD5Encrypt(string pToEncrypt, string sKey)
{
DESCryptoServiceProvider des = new DESCryptoServiceProvider();
byte[] inputByteArray = Encoding.Default.GetBytes(pToEncrypt);
des.Key = ASCIIEncoding.ASCII.GetBytes(sKey);
des.IV = ASCIIEncoding.ASCII.GetBytes(sKey);
MemoryStream ms = new MemoryStream();
CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(), CryptoStreamMode.Write);
cs.Write(inputByteArray, 0, inputByteArray.Length);
cs.FlushFinalBlock();
StringBuilder ret = new StringBuilder();
foreach (byte b in ms.ToArray())
{
ret.AppendFormat("{0:X2}", b);
}
ret.ToString();
return ret.ToString();
}

/// <summary>
/// 解密
/// </summary>
/// <param name="pToDecrypt"></param>
/// <param name="sKey"></param>
/// <returns></returns>
public static string MD5Decrypt(string pToDecrypt, string sKey)
{
string text = "";
try
{
DESCryptoServiceProvider des = new DESCryptoServiceProvider();

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

des.Key = ASCIIEncoding.ASCII.GetBytes(sKey);
des.IV = ASCIIEncoding.ASCII.GetBytes(sKey);
MemoryStream ms = new MemoryStream();
CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(), CryptoStreamMode.Write);
cs.Write(inputByteArray, 0, inputByteArray.Length);
cs.FlushFinalBlock();

StringBuilder ret = new StringBuilder();
text = System.Text.Encoding.Default.GetString(ms.ToArray());
}
catch
{
text = pToDecrypt;
}
return text;
}