1、（1）3des算法介绍
3DES算法是指使用双长度（16字节）密钥K＝（KL||KR）将8字节明文数据块进行3次DES加密/解密。如下所示：
Y ＝ DES(KL)[DES-1(KR)[DES(KL[X])]]
解密方式为：
X ＝ DES-1 (KL)[DES (KR)[ DES-1 (KL[Y])]]
其中，DES(KL[X])表示用密钥K对数据X进行DES加密，DES-1 (KL[Y])表示用密钥K对数据Y进行解密。
SessionKey的计算采用3DES算法，计算出单倍长度的密钥。表示法为:SK = Session(DK，DATA)
3DES加密算法为：
VOID 3DES(BYTE DoubleKeyStr[16]， BYTE Data[8]， BYTE Out[8])
{
BYTE Buf1[8]， Buf2[8];
DES (&DoubleKeyStr[0]， Data， Buf1);
UDES(&DoubleKeyStr[8]， Buf1， Buf2);
DES (&DoubleKeyStr[0]， Buf2， Out);
}
（2）3des+base64加密与解密示例
设Ek()和Dk()代表DES算法的加密和解密过程，K代表DES算法使用的密钥，P代表明文，C代表密表，这样，
3DES加密过程为：C=Ek3(Dk2(Ek1(P)))
3DES解密过程为：P=Dk1((EK2(Dk3(C)))
具体的加/解密过程如下所示。
using System;
using System.Text;
using System.IO;
using System.Security.Cryptography;
class Class1
{
static void Main()
{
Console.WriteLine("Encrypt String...");
txtKey = "tkGGRmBErvc=";
btnKeyGen();
Console.WriteLine("Encrypt Key :",txtKey);
txtIV = "Kl7ZgtM1dvQ=";
btnIVGen();
Console.WriteLine("Encrypt IV :",txtIV);
Console.WriteLine();
string txtEncrypted = EncryptString("1111");
Console.WriteLine("Encrypt String : ",txtEncrypted);
string txtOriginal = DecryptString(txtEncrypted);
Console.WriteLine("Decrypt String : ",txtOriginal);
}
private static SymmetricAlgorithm mCSP;
private static string txtKey;
private static string txtIV;
private static void btnKeyGen()
{
mCSP = SetEnc();
byte[] byt2 = Convert.FromBase64String(txtKey);
mCSP.Key = byt2;
}
private static void btnIVGen()
{
byte[] byt2 = Convert.FromBase64String(txtIV);
mCSP.IV = byt2;
}
private static string EncryptString(string Value)
{
ICryptoTransform ct;
MemoryStream ms;
CryptoStream cs;
byte[] byt;
ct = mCSP.CreateEncryptor(mCSP.Key, mCSP.IV);
byt = Encoding.UTF8.GetBytes(Value);
ms = new MemoryStream();
cs = new CryptoStream(ms, ct, CryptoStreamMode.Write);
cs.Write(byt, 0, byt.Length);
cs.FlushFinalBlock();
cs.Close();
return Convert.ToBase64String(ms.ToArray());
}
private static string DecryptString(string Value)
{
ICryptoTransform ct;
MemoryStream ms;
CryptoStream cs;
byte[] byt;
ct = mCSP.CreateDecryptor(mCSP.Key, mCSP.IV);
byt = Convert.FromBase64String(Value);
ms = new MemoryStream();
cs = new CryptoStream(ms, ct, CryptoStreamMode.Write);
cs.Write(byt, 0, byt.Length);
cs.FlushFinalBlock();
cs.Close();
return Encoding.UTF8.GetString(ms.ToArray());
}
private static SymmetricAlgorithm SetEnc()
{
return new DESCryptoServiceProvider();
}
}
K1、K2、K3决定了算法的安全性，若三个密钥互不相同，本质上就相当于用一个长为168位的密钥进行加密。多年来，它在对付强力攻击时是比较安全的。若数据对安全性要求不那么高，K1可以等于K3。在这种情况下，密钥的有效长度为112位。
（3）java与C#加密与解密对比
java中的Cipher.DECRYPR_MODE
import javax.crypto.Cipher;
public class CryptionData
{ // The length of Encryptionstring should be 24 byte and not be a weak key private string EncryptionString; // The length of initialization vector should be 8 byte private static Byte[] EncryptionIV = Encoding.Default.GetBytes(" "); /// <summary> /// Constructor /// </summary> public CryptionData()
{ } /// <summary> /// Constructor /// </summary> /// <param name="EncryptionString">SecureKey</param> public CryptionData(string EncryptionString) { this.EncryptionString = EncryptionString; } /// <summary> /// Encryption method for byte array /// </summary> /// <param name="SourceData">source data</param> /// <returns>byte array</returns> public byte[] EncryptionByteData(byte[] SourceData) { byte[] returnData = null; try { // Create TripleDESCryptoServiceProvider object TripleDESCryptoServiceProvider desProvider = new TripleDESCryptoServiceProvider(); // Set SecureKey and IV of desProvider byte[] byteKey = Encoding.Default.GetBytes(EncryptionString); desProvider.Key = byteKey; desProvider.IV = EncryptionIV; desProvider.Mode = CipherMode.ECB; // A MemoryStream object MemoryStream ms = new MemoryStream(); // Create Encryptor ICryptoTransform encrypto = desProvider.CreateEncryptor(); // Create CryptoStream object CryptoStream cs = new CryptoStream(ms, encrypto, CryptoStreamMode.Write); // Encrypt SourceData cs.Write(SourceData, 0, SourceData.Length); cs.FlushFinalBlock(); // Get Encryption result returnData = ms.ToArray(); } catch (Exception ex) { throw ex; } return returnData; } /// <summary> /// Decryption method for byte array /// </summary> /// <param name="SourceData">source data</param> /// <returns>byte array</returns> public byte[] DecryptionByteData(byte[] SourceData) { byte[] returnData = null; try { // Create TripleDESCryptoServiceProvider object TripleDESCryptoServiceProvider desProvider = new TripleDESCryptoServiceProvider(); // Set SecureKey and IV of desProvider byte[] byteKey = Encoding.Default.GetBytes(EncryptionString); desProvider.Key = byteKey; desProvider.IV = EncryptionIV; desProvider.Mode = CipherMode.ECB; // A MemoryStream object MemoryStream ms = new MemoryStream(); // Create Decryptor ICryptoTransform encrypto = desProvider.CreateDecryptor(); // Create CryptoStream object CryptoStream cs = new CryptoStream(ms, encrypto, CryptoStreamMode.Write); // Decrypt SourceData cs.Write(SourceData, 0, SourceData.Length); cs.FlushFinalBlock(); // Get Decryption result returnData = ms.ToArray(); } catch (Exception ex) { throw ex; } return returnData; } /// <summary> /// Encryption method for string /// </summary> /// <param name="SourceData">source data</param> /// <returns>string</returns> public string EncryptionStringData(string SourceData) { try { // Convert source data from string to byte array byte[] SourData = Encoding.Default.GetBytes(SourceData); // Encrypt byte array byte[] retData = EncryptionByteData(SourData); // Convert encryption result from byte array to Base64String return Convert.ToBase64String(retData, 0, retData.Length); } catch (Exception ex) { throw ex; } } /// <summary> /// Decryption method for string /// </summary> /// <param name="SourceData">source data</param> /// <returns>string</returns> public string DecryptionStringdata(string SourceData) { try { // Convert source data from Base64String to byte array byte[] SourData = Convert.FromBase64String(SourceData); // Decrypt byte array byte[] retData = DecryptionByteData(SourData); // Convert Decryption result from byte array to string return Encoding.Default.GetString(retData, 0, retData.Length); } catch (Exception ex) { throw ex; } }}