在.net Flamework完全版中对System.Security.Cryptography名字空间下的加密类支持得很好。但在精简版中却没有提供这个名字空间中的相应的类。在用.net写Pocket PC程序的时候用的加密算法的时候确实比较麻烦。一般有两种方法来解决这个问题。OpenNetCF（www.openetcf.org）提供了System.Security.Cryptography名字空间下的各个类的模拟,但它的提供缺乏灵活性：比如在对称加密的时候，用户无法设置Padding, CipherMode等属性。而且它的提供方式和完全版的.net下的类的接口不一致，这样给用户造成困惑。另一种方法就是自己动手对cryptoAPI进行自己封装。

最近出于工作需要对MD5CryptoServiceProvider进行了实现，这个类的接口和完整版下面的接口完全一致。

Implementation of the "System.Security.Cryptography.MD5CryptoServiceProvider" class.

public sealed class MD5CryptoServiceProvider : MD5

     {

         public MD5CryptoServiceProvider()

         {

              Initialize();

              m_Disposed = false;

         }

         public override void Initialize()

         {

              if (m_Disposed)

                   throw new ObjectDisposedException(this.GetType().FullName);

              if (m_Hash != IntPtr.Zero)

              {

                   Crypto.CryptDestroyHash(m_Hash);

              }

              m_Prov = Crypto.AcquireContext(ProvType.RSA_FULL);

              bool retVal=Crypto.CryptCreateHash(m_Prov, (uint)CalgHash.MD5, IntPtr.Zero, 0, out m_Hash);

         }

         protected override void HashCore(byte[] array, int ibStart, int cbSize)

         {

              if (m_Disposed)

                   throw new ObjectDisposedException(this.GetType().FullName);

              byte[] copy = (byte[]) array.Clone();

              //Array.Copy(array, ibStart, copy, 0, cbSize);

              bool retVal=false;

              retVal=Crypto.CryptHashData(m_Hash, copy, copy.Length, 0);

         }

         protected override byte[] HashFinal()

         {

              if (m_Disposed)

                   throw new ObjectDisposedException(this.GetType().FullName);

              byte [] data = new byte[0];

              uint dataLen = 0;

              uint flags = 0;

              //size

              bool retVal = Crypto.CryptGetHashParam(m_Hash, (uint) HashParam.HASHVAL, data, ref dataLen, flags);

              if(234 == Marshal.GetLastWin32Error())//MORE_DATA                = 234,

              {

                   //data

                   data = new byte[dataLen];

                   retVal = Crypto.CryptGetHashParam(m_Hash, (uint) HashParam.HASHVAL, data, ref dataLen, flags);

              }

              return data;

         }

         protected override void Dispose(bool disposing)

         {

              if (!m_Disposed)

              {

                   if (m_Hash != IntPtr.Zero)

                   {

                       bool retVal=Crypto.CryptDestroyHash(m_Hash);

                       m_Hash = IntPtr.Zero;

                   }

                   if(m_Prov!=IntPtr.Zero)

                   {

                       Crypto.CryptReleaseContext(m_Prov, 0);

                       m_Prov=IntPtr.Zero;

                   }

                   try

                   {

                       GC.SuppressFinalize(this);

                   }

                   catch {}

                   m_Disposed = true;

              }

         }

         ~MD5CryptoServiceProvider()

         {

              Clear();

         }

         private IntPtr m_Hash=IntPtr.Zero;

         private bool m_Disposed;

         private IntPtr m_Prov=IntPtr.Zero;

     }

public abstract class MD5 : HashAlgorithm

     {

         // Constructor.

         protected MD5()

                   {

                       HashSizeValue = 128;

                   }

         // Create a new instance of the "MD5" class.

         public new static MD5 Create()

                   {

                       return (MD5)(CryptoConfig.CreateFromName

                                 (CryptoConfig.MD5Default, null));

                   }

         public new static MD5 Create(String algName)

                   {

                       return (MD5)(CryptoConfig.CreateFromName(algName, null));

                   }

     }; // class MD5

P/Invoke the cryotoAPI

public class Crypto

     {

         [DllImport("coredll.dll", EntryPoint="CryptAcquireContext")]

         public static extern bool CryptAcquireContext(out IntPtr hProv, string pszContainer, string pszProvider, uint dwProvType, uint dwFlags);

         [DllImport("coredll.dll", EntryPoint="CryptCreateHash")]

         public static extern bool CryptCreateHash(IntPtr hProv, uint Algid, IntPtr hKey, uint dwFlags, out IntPtr phHash);

         [DllImport("coredll.dll", EntryPoint="CryptDestroyHash")]

         public static extern bool CryptDestroyHash(IntPtr hHash);

         [DllImport("coredll.dll", EntryPoint="CryptHashData")]

         public static extern bool CryptHashData(IntPtr hHash, byte[] pbData, int dwDataLen, uint dwFlags);

         [DllImport("coredll.dll", EntryPoint="CryptGetHashParam", SetLastError=true)]           

         public static extern bool CryptGetHashParam(IntPtr hHash, uint dwParam, byte[] pbData, ref uint pdwDataLen, uint dwFlags);

         [DllImport("coredll.dll", EntryPoint="CryptReleaseContext")]

         public static extern bool CryptReleaseContext(IntPtr hProv, uint dwFlags);

         public static IntPtr AcquireContext()

         {

              return AcquireContext("MD5Container",  ProvName.MS_ENHANCED_PROV,  ProvType.RSA_FULL, ContextFlag.NONE);

         }

         public static IntPtr AcquireContext(string container)

         {

              return AcquireContext(container,  ProvName.MS_ENHANCED_PROV,  ProvType.RSA_FULL, ContextFlag.NONE);

         }

         public static IntPtr AcquireContext(ProvType provType)

         {

              return AcquireContext(null, null, provType, ContextFlag.NONE);

         }

         public static IntPtr AcquireContext(string provName, ProvType provType)

         {

              return AcquireContext(null, provName, provType, ContextFlag.NONE);

         }

         public static IntPtr AcquireContext(string provName, ProvType provType, ContextFlag conFlag)

         {

              return AcquireContext(null, provName, provType, conFlag);

         }

         public static IntPtr AcquireContext(string conName, string provName, ProvType provType)

         {

              return AcquireContext(conName, provName, provType, ContextFlag.NONE);

          }

         public static IntPtr AcquireContext(string conName, string provName, ProvType provType, ContextFlag conFlag)

         {

              IntPtr hProv;

              bool retVal = Crypto.CryptAcquireContext(out hProv, conName, provName, (uint) provType, (uint) conFlag);

              if(!retVal) //try creating a new key container

              {

                   retVal = Crypto.CryptAcquireContext(out hProv, conName, provName, (uint) provType, (uint) ContextFlag.NEWKEYSET);

              }

              if(hProv == IntPtr.Zero)

                   throw new Exception("System.Security.Cryptography");

              return hProv;

         }

     }

代码下载在codeproject上有：http://www.codeproject.com/useritems/MD5CryptoServiceProvider.asp

Reference:

Dot NET Compact Framework Kick Start 2003

www.opennetcf.org

http://www.koders.com/csharp/fidC21861B5F1B717EC1FDEC006DBD0B8226B92D878.aspx