public string MD5Encrypt(string objStr)
  {
   //獲取要加密的欄位，經過編碼後（必須），並轉化為Byte[]陣列
   byte[] data= Encoding.Default.GetBytes(objStr);
   //建立加密服務
   System.Security.Cryptography.MD5 md5 = new System.Security.Cryptography.MD5CryptoServiceProvider();   
   //加密Byte[]陣列
   byte[] result= md5.ComputeHash(data);
   //將加密後的陣列以16進位制轉化為普遍字串
   StringBuilder sBuilder = new StringBuilder();
   for (int i = 0; i < result.Length; i++)
   {
    sBuilder.Append(result[i].ToString("x2"));
   }
   //顯示出來
   return sBuilder.ToString();
  } 

Delphi的MD5加密麻煩很多,他本身沒有這個函式庫的支援.下面的單元是從網上抄的.

{
1、 MD5String、MD5File、MD5Print、MD5Match這四個函式是供呼叫的。其他是用來輔助這幾個函式的子函式。
2、MD5String為加密字串。
3、MD5File為加密這個檔案。
4、MD5Print是將加密後的密文轉換成字串。
5、MD5Match是用來比較密文是否一致。

加密字串aaa             MD5String('aaa')
將加密後的aaa顯示出來     MD5Print(MD5String('aaa'))
比較兩次密文是否一致：    MD5Match(MD5String('第一次明文'),MD5String('第二次輸入的明文'))
}
// tabs = 2
// -----------------------------------------------------------------------------------------------
//
//                                 MD5 Message-Digest for Delphi
//
//                                 Delphi  Unit implementing the
//                      RSA Data Security, Inc. MD5 Message-Digest Algorithm
//
//                          Implementation of Ronald L. Rivest's RFC 1321
//
//                      Copyright ?1997-1999 Medienagentur Fichtner & Meyer
//                                  Written by Matthias Fichtner
//
// -----------------------------------------------------------------------------------------------
//               See RFC 1321 for RSA Data Security's copyright and license notice!
// -----------------------------------------------------------------------------------------------
//
//     14-Jun-97  mf  Implemented MD5 according to RFC 1321                           RFC 1321
//     16-Jun-97  mf  Initial release of the compiled unit (no source code)           RFC 1321
//     28-Feb-99  mf  Added MD5Match function for comparing two digests               RFC 1321
//     13-Sep-99  mf  Reworked the entire unit                                        RFC 1321
//     17-Sep-99  mf  Reworked the "Test Driver" project                              RFC 1321
//     19-Sep-99  mf  Release of sources for MD5 unit and "Test Driver" project       RFC 1321
//
// -----------------------------------------------------------------------------------------------
//                   The latest release of md5.pas will always be available from
//                  the distribution site at:

http://www.fichtner.net/delphi/md5/
// -----------------------------------------------------------------------------------------------
//                       Please send questions, bug reports and suggestions
//                      regarding this code to: [email protected]
// -----------------------------------------------------------------------------------------------
//                        This code is provided "as is" without express or
//                     implied warranty of any kind. Use it at your own risk.
// -----------------------------------------------------------------------------------------------

unit md5;

// -----------------------------------------------------------------------------------------------
INTERFACE
// -----------------------------------------------------------------------------------------------

uses
 Windows;

type
 MD5Count = array[0..1] of DWORD;
 MD5State = array[0..3] of DWORD;
 MD5Block = array[0..15] of DWORD;
 MD5CBits = array[0..7] of byte;
 MD5Digest = array[0..15] of byte;
 MD5Buffer = array[0..63] of byte;
 MD5Context = record
   State: MD5State;
   Count: MD5Count;
   Buffer: MD5Buffer;
 end;

procedure MD5Init(var Context: MD5Context);
procedure MD5Update(var Context: MD5Context; Input: pChar; Length: longword);
procedure MD5Final(var Context: MD5Context; var Digest: MD5Digest);

function MD5String(M: string): MD5Digest;
function MD5File(N: string): MD5Digest;
function MD5Print(D: MD5Digest): string;

function MD5Match(D1, D2: MD5Digest): boolean;

// -----------------------------------------------------------------------------------------------
IMPLEMENTATION
// -----------------------------------------------------------------------------------------------

var
 PADDING: MD5Buffer = (
   $80, $00, $00, $00, $00, $00, $00, $00,
   $00, $00, $00, $00, $00, $00, $00, $00,
   $00, $00, $00, $00, $00, $00, $00, $00,
   $00, $00, $00, $00, $00, $00, $00, $00,
   $00, $00, $00, $00, $00, $00, $00, $00,
   $00, $00, $00, $00, $00, $00, $00, $00,
   $00, $00, $00, $00, $00, $00, $00, $00,
   $00, $00, $00, $00, $00, $00, $00, $00
 );

function F(x, y, z: DWORD): DWORD;
begin
 Result := (x and y) or ((not x) and z);
end;

function G(x, y, z: DWORD): DWORD;
begin
 Result := (x and z) or (y and (not z));
end;

function H(x, y, z: DWORD): DWORD;
begin
 Result := x xor y xor z;
end;

function I(x, y, z: DWORD): DWORD;
begin
 Result := y xor (x or (not z));
end;

procedure rot(var x: DWORD; n: BYTE);
begin
 x := (x shl n) or (x shr (32 - n));
end;

procedure FF(var a: DWORD; b, c, d, x: DWORD; s: BYTE; ac: DWORD);
begin
 inc(a, F(b, c, d) + x + ac);
 rot(a, s);
 inc(a, b);
end;

procedure GG(var a: DWORD; b, c, d, x: DWORD; s: BYTE; ac: DWORD);
begin
 inc(a, G(b, c, d) + x + ac);
 rot(a, s);
 inc(a, b);
end;

procedure HH(var a: DWORD; b, c, d, x: DWORD; s: BYTE; ac: DWORD);
begin
 inc(a, H(b, c, d) + x + ac);
 rot(a, s);
 inc(a, b);
end;

procedure II(var a: DWORD; b, c, d, x: DWORD; s: BYTE; ac: DWORD);
begin
 inc(a, I(b, c, d) + x + ac);
 rot(a, s);
 inc(a, b);
end;

// -----------------------------------------------------------------------------------------------

// Encode Count bytes at Source into (Count / 4) DWORDs at Target
procedure Encode(Source, Target: pointer; Count: longword);
var
 S: PByte;
 T: PDWORD;
 I: longword;
begin
 S := Source;
 T := Target;
 for I := 1 to Count div 4 do begin
   T^ := S^;
   inc(S);
   T^ := T^ or (S^ shl 8);
   inc(S);
   T^ := T^ or (S^ shl 16);
   inc(S);
   T^ := T^ or (S^ shl 24);
   inc(S);
   inc(T);
 end;
end;

// Decode Count DWORDs at Source into (Count * 4) Bytes at Target
procedure Decode(Source, Target: pointer; Count: longword);
var
 S: PDWORD;
 T: PByte;
 I: longword;
begin
 S := Source;
 T := Target;
 for I := 1 to Count do begin
   T^ := S^ and $ff;
   inc(T);
   T^ := (S^ shr 8) and $ff;
   inc(T);
   T^ := (S^ shr 16) and $ff;
   inc(T);
   T^ := (S^ shr 24) and $ff;
   inc(T);
   inc(S);
 end;
end;

// Transform State according to first 64 bytes at Buffer
procedure Transform(Buffer: pointer; var State: MD5State);
var
 a, b, c, d: DWORD;
 Block: MD5Block;
begin
 Encode(Buffer, @Block, 64);
 a := State[0];
 b := State[1];
 c := State[2];
 d := State[3];
 FF (a, b, c, d, Block[ 0],  7, $d76aa478);
 FF (d, a, b, c, Block[ 1], 12, $e8c7b756);
 FF (c, d, a, b, Block[ 2], 17, $242070db);
 FF (b, c, d, a, Block[ 3], 22, $c1bdceee);
 FF (a, b, c, d, Block[ 4],  7, $f57c0faf);
 FF (d, a, b, c, Block[ 5], 12, $4787c62a);
 FF (c, d, a, b, Block[ 6], 17, $a8304613);
 FF (b, c, d, a, Block[ 7], 22, $fd469501);
 FF (a, b, c, d, Block[ 8],  7, $698098d8);
 FF (d, a, b, c, Block[ 9], 12, $8b44f7af);
 FF (c, d, a, b, Block[10], 17, $ffff5bb1);
 FF (b, c, d, a, Block[11], 22, $895cd7be);
 FF (a, b, c, d, Block[12],  7, $6b901122);
 FF (d, a, b, c, Block[13], 12, $fd987193);
 FF (c, d, a, b, Block[14], 17, $a679438e);
 FF (b, c, d, a, Block[15], 22, $49b40821);
 GG (a, b, c, d, Block[ 1],  5, $f61e2562);
 GG (d, a, b, c, Block[ 6],  9, $c040b340);
 GG (c, d, a, b, Block[11], 14, $265e5a51);
 GG (b, c, d, a, Block[ 0], 20, $e9b6c7aa);
 GG (a, b, c, d, Block[ 5],  5, $d62f105d);
 GG (d, a, b, c, Block[10],  9,  $2441453);
 GG (c, d, a, b, Block[15], 14, $d8a1e681);
 GG (b, c, d, a, Block[ 4], 20, $e7d3fbc8);
 GG (a, b, c, d, Block[ 9],  5, $21e1cde6);
 GG (d, a, b, c, Block[14],  9, $c33707d6);
 GG (c, d, a, b, Block[ 3], 14, $f4d50d87);
 GG (b, c, d, a, Block[ 8], 20, $455a14ed);
 GG (a, b, c, d, Block[13],  5, $a9e3e905);
 GG (d, a, b, c, Block[ 2],  9, $fcefa3f8);
 GG (c, d, a, b, Block[ 7], 14, $676f02d9);
 GG (b, c, d, a, Block[12], 20, $8d2a4c8a);
 HH (a, b, c, d, Block[ 5],  4, $fffa3942);
 HH (d, a, b, c, Block[ 8], 11, $8771f681);
 HH (c, d, a, b, Block[11], 16, $6d9d6122);
 HH (b, c, d, a, Block[14], 23, $fde5380c);
 HH (a, b, c, d, Block[ 1],  4, $a4beea44);
 HH (d, a, b, c, Block[ 4], 11, $4bdecfa9);
 HH (c, d, a, b, Block[ 7], 16, $f6bb4b60);
 HH (b, c, d, a, Block[10], 23, $bebfbc70);
 HH (a, b, c, d, Block[13],  4, $289b7ec6);
 HH (d, a, b, c, Block[ 0], 11, $eaa127fa);
 HH (c, d, a, b, Block[ 3], 16, $d4ef3085);
 HH (b, c, d, a, Block[ 6], 23,  $4881d05);
 HH (a, b, c, d, Block[ 9],  4, $d9d4d039);
 HH (d, a, b, c, Block[12], 11, $e6db99e5);
 HH (c, d, a, b, Block[15], 16, $1fa27cf8);
 HH (b, c, d, a, Block[ 2], 23, $c4ac5665);
 II (a, b, c, d, Block[ 0],  6, $f4292244);
 II (d, a, b, c, Block[ 7], 10, $432aff97);
 II (c, d, a, b, Block[14], 15, $ab9423a7);
 II (b, c, d, a, Block[ 5], 21, $fc93a039);
 II (a, b, c, d, Block[12],  6, $655b59c3);
 II (d, a, b, c, Block[ 3], 10, $8f0ccc92);
 II (c, d, a, b, Block[10], 15, $ffeff47d);
 II (b, c, d, a, Block[ 1], 21, $85845dd1);
 II (a, b, c, d, Block[ 8],  6, $6fa87e4f);
 II (d, a, b, c, Block[15], 10, $fe2ce6e0);
 II (c, d, a, b, Block[ 6], 15, $a3014314);
 II (b, c, d, a, Block[13], 21, $4e0811a1);
 II (a, b, c, d, Block[ 4],  6, $f7537e82);
 II (d, a, b, c, Block[11], 10, $bd3af235);
 II (c, d, a, b, Block[ 2], 15, $2ad7d2bb);
 II (b, c, d, a, Block[ 9], 21, $eb86d391);
 inc(State[0], a);
 inc(State[1], b);
 inc(State[2], c);
 inc(State[3], d);
end;

// -----------------------------------------------------------------------------------------------

// Initialize given Context
procedure MD5Init(var Context: MD5Context);
begin
 with Context do begin
   State[0] := $67452301;
   State[1] := $efcdab89;
   State[2] := $98badcfe;
   State[3] := $10325476;
   Count[0] := 0;
   Count[1] := 0;
   ZeroMemory(@Buffer, SizeOf(MD5Buffer));
 end;
end;

// Update given Context to include Length bytes of Input
procedure MD5Update(var Context: MD5Context; Input: pChar; Length: longword);
var
 Index: longword;
 PartLen: longword;
 I: longword;
begin
 with Context do begin
   Index := (Count[0] shr 3) and $3f;
   inc(Count[0], Length shl 3);
   if Count[0] < (Length shl 3) then inc(Count[1]);
   inc(Count[1], Length shr 29);
 end;
 PartLen := 64 - Index;
 if Length >= PartLen then begin
   CopyMemory(@Context.Buffer[Index], Input, PartLen);
   Transform(@Context.Buffer, Context.State);
   I := PartLen;
   while I + 63 < Length do begin
     Transform(@Input[I], Context.State);
     inc(I, 64);
   end;
   Index := 0;
 end else I := 0;
 CopyMemory(@Context.Buffer[Index], @Input[I], Length - I);
end;

// Finalize given Context, create Digest and zeroize Context
procedure MD5Final(var Context: MD5Context; var Digest: MD5Digest);
var
 Bits: MD5CBits;
 Index: longword;
 PadLen: longword;
begin
 Decode(@Context.Count, @Bits, 2);
 Index := (Context.Count[0] shr 3) and $3f;
 if Index < 56 then PadLen := 56 - Index else PadLen := 120 - Index;
 MD5Update(Context, @PADDING, PadLen);
 MD5Update(Context, @Bits, 8);
 Decode(@Context.State, @Digest, 4);
 ZeroMemory(@Context, SizeOf(MD5Context));
end;

// -----------------------------------------------------------------------------------------------

// Create digest of given Message
function MD5String(M: string): MD5Digest;
var
 Context: MD5Context;
begin
 MD5Init(Context);
 MD5Update(Context, pChar(M), length(M));
 MD5Final(Context, Result);
end;

// Create digest of file with given Name
function MD5File(N: string): MD5Digest;
var
 FileHandle: THandle;
 MapHandle: THandle;
 ViewPointer: pointer;
 Context: MD5Context;
begin
 MD5Init(Context);
 FileHandle := CreateFile(pChar(N), GENERIC_READ, FILE_SHARE_READ or FILE_SHARE_WRITE,
   nil, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL or FILE_FLAG_SEQUENTIAL_SCAN, 0);
 if FileHandle <> INVALID_HANDLE_VALUE then try
   MapHandle := CreateFileMapping(FileHandle, nil, PAGE_READONLY, 0, 0, nil);
   if MapHandle <> 0 then try
     ViewPointer := MapViewOfFile(MapHandle, FILE_MAP_READ, 0, 0, 0);
     if ViewPointer <> nil then try
       MD5Update(Context, ViewPointer, GetFileSize(FileHandle, nil));
     finally
       UnmapViewOfFile(ViewPointer);
     end;
   finally
     CloseHandle(MapHandle);
   end;
 finally
   CloseHandle(FileHandle);
 end;
 MD5Final(Context, Result);
end;

// Create hex representation of given Digest
function MD5Print(D: MD5Digest): string;
var
 I: byte;
const
 Digits: array[0..15] of char =
   ('0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f');
begin
 Result := '';
 for I := 0 to 15 do Result := Result + Digits[(D[I] shr 4) and $0f] + Digits[D[I] and $0f];
end;

// -----------------------------------------------------------------------------------------------

// Compare two Digests
function MD5Match(D1, D2: MD5Digest): boolean;
var
 I: byte;
begin
 I := 0;
 Result := TRUE;
 while Result and (I < 16) do begin
   Result := D1[I] = D2[I];
   inc(I);
 end;
end;

end.