Base64 (MIME) Encode and Decode

Problem/Question/Abstract:

This article gives you two routines allowing for fast encoding and decoding in and out of the MIME format.

Answer:

I have written the following unit to replace the INDY TIdEncoderMIME and TIdDecoderMIME components. This "Codec" is used in Email-Software, primarely.

First reason was the lack of speed of these components. Second reason was, that they are components and therefore require the VCL - an heavy extra load on otherwise nonVCL systems.

Both routines are written in Assembler and overloaded by different versions allowing for easy access.

I am sure, some of your are able to increase the speed even some more. Please let me know. Thanks.

I have introduced a compiler switch to switch between a fast decoding mode and a more secure decoding mode. It is up to you, which you like to use. I recomend using the more secure mode, especially if the user is required to work with the encoded data.

{* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
*
* Unit Name : uBase64Codec
* Author    : Daniel Wischnewski
* Copyright : Copyright © 2001-2003 by gate(n)etwork GmbH. All Rights Reserved.
* Creator   : Daniel Wischnewski
* Contact   : Daniel Wischnewski (e-mail: delphi3000(at)wischnewski.tv);
*
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *}

//                               * * * License * * *
//
// The contents of this file are used with permission, subject to the Mozilla
// Public License Version 1.1 (the "License"); you may not use this file except
// in compliance with the License. You may obtain a copy of the License at
//
//                       http://www.mozilla.org/MPL/MPL-1.1.html
//
// Software distributed under the License is distributed on an "AS IS" basis,
// WITHOUT WARRANTY OF ANY KIND, either express or  implied. See the License for
// the specific language governing rights and limitations under the License.
//

//                               * * * My Wish * * *
//
// If you come to use this unit for your work, I would like to know about it.
// Drop me an e-mail and let me know how it worked out for you. If you wish, you
// can send me a copy of your work. No obligations!
// My e-mail address: delphi3000(at)wischnewski.tv
//

//                               * * * History * * *
//
// Version 1.0 (Oct-10 2002)
//    first published on Delphi-PRAXiS (www.delphipraxis.net)
//
// Version 1.1 (May-13 2003)
//    introduced a compiler switch (SpeedDecode) to switch between a faster
//    decoding variant (prior version) and a litte less fast, but secure variant
//    to work around bad formatted data (decoding only!)
//

unit Base64;

interface

// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
// !! THE COMPILER SWITCH MAY BE USED TO ADJUST THE BEHAVIOR !!
// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

// enable "SpeedDecode"
//     the switch to gain speed while decoding the message, however, the codec
//     will raise different exceptions/access violations or invalid output if
//     the incoming data is invalid or missized.

// disable "SpeedDecode"
//     the switch to enable a data check, that will scan the data to decode to
//     be valid. This method is to be used if you cannot guarantee to validity
//     of the data to be decoded.

{.DEFINE SpeedDecode}

{$IFNDEF SpeedDecode}
{$DEFINE ValidityCheck}
{$ENDIF}

uses SysUtils;

// codiert einen String in die zugeh�rige Base64-Darstellung
function Base64Encode(const InText: AnsiString): AnsiString; overload;
// decodiert die Base64-Darstellung eines Strings in den zugeh�rigen String
function Base64Decode(const InText: AnsiString): AnsiString; overload;

// bestimmt die Gr��e der Base64-Darstellung
function CalcEncodedSize(InSize: Cardinal): Cardinal;
// bestimmt die Gr��e der bin�ren Darstellung
function CalcDecodedSize(const InBuffer; InSize: Cardinal): Cardinal;

// codiert einen Buffer in die zugeh�rige Base64-Darstellung
procedure Base64Encode(const InBuffer; InSize: Cardinal; var OutBuffer); overload;
  register;
// decodiert die Base64-Darstellung in einen Buffer
{$IFDEF SpeedDecode}
procedure Base64Decode(const InBuffer; InSize: Cardinal; var OutBuffer); overload;
  register;
{$ENDIF}
{$IFDEF ValidityCheck}
function Base64Decode(const InBuffer; InSize: Cardinal; var OutBuffer): Boolean;
  overload; register;
{$ENDIF}

// codiert einen String in die zugeh�rige Base64-Darstellung
procedure Base64Encode(const InText: PAnsiChar; var OutText: PAnsiChar); overload;
// decodiert die Base64-Darstellung eines Strings in den zugeh�rigen String
procedure Base64Decode(const InText: PAnsiChar; var OutText: PAnsiChar); overload;

// codiert einen String in die zugeh�rige Base64-Darstellung
procedure Base64Encode(const InText: AnsiString; var OutText: AnsiString); overload;
// decodiert die Base64-Darstellung eines Strings in den zugeh�rigen String
procedure Base64Decode(const InText: AnsiString; var OutText: AnsiString); overload;

implementation

const
  cBase64Codec: array[0..63] of AnsiChar =
  'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
  Base64Filler = '=';

function Base64Encode(const InText: string): string; overload;
begin
  Base64Encode(InText, Result);
end;

function Base64Decode(const InText: string): string; overload;
begin
  Base64Decode(InText, Result);
end;

function CalcEncodedSize(InSize: Cardinal): Cardinal;
begin
  // no buffers passed along, calculate outbuffer size needed
  Result := (InSize div 3) shl 2;
  if ((InSize mod 3) > 0) then
    Inc(Result, 4);
end;

function CalcDecodedSize(const InBuffer; InSize: Cardinal): Cardinal;
type
  BA = array of Byte;
begin
  Result := 0;
  if InSize = 0 then
    Exit;
  if InSize mod 4 <> 0 then
    Exit;
  Result := InSize div 4 * 3;
  if (BA(InBuffer)[InSize - 2] = Ord(Base64Filler)) then
    Dec(Result, 2)
  else if BA(InBuffer)[InSize - 1] = Ord(Base64Filler) then
    Dec(Result);
end;

procedure Base64Encode(const InBuffer; InSize: Cardinal; var OutBuffer
  ); register;
var
  ByThrees, LeftOver: Cardinal;
  // reset in- and outbytes positions
asm
  // load addresses for source and destination
  // PBYTE(InBuffer);
  mov  ESI, [EAX]
  // PBYTE(OutBuffer);
  mov  EDI, [ECX]
  // ByThrees := InSize div 3;
  // LeftOver := InSize mod 3;
  // load InSize (stored in EBX)
  mov  EAX, EBX
  // load 3
  mov  ECX, $03
  // clear upper 32 bits
  xor  EDX, EDX
  // divide by ECX
  div  ECX
  // save result
  mov  ByThrees, EAX
  // save remainder
  mov  LeftOver, EDX
  // load addresses
  lea  ECX, cBase64Codec[0]
  // while I < ByThrees do
  // begin
  xor  EAX, EAX
  xor  EBX, EBX
  xor  EDX, EDX
  cmp  ByThrees, 0
  jz   @@LeftOver
  @@LoopStart:
    // load the first two bytes of the source triplet
    LODSW
    // write Bits 0..5 to destination
    mov  BL, AL
    shr  BL, 2
    mov  DL, BYTE PTR [ECX + EBX]
    // save the Bits 12..15 for later use [1]
    mov  BH, AH
    and  BH, $0F
    // save Bits 6..11
    rol  AX, 4
    and  AX, $3F
    mov  DH, BYTE PTR [ECX + EAX]
    mov  AX, DX
    // store the first two bytes of the destination quadruple
    STOSW
    // laod last byte (Bits 16..23) of the source triplet
    LODSB
    // extend bits 12..15 [1] with Bits 16..17 and save them
    mov  BL, AL
    shr  BX, 6
    mov  DL, BYTE PTR [ECX + EBX]
    // save bits 18..23
    and  AL, $3F
    xor  AH, AH
    mov  DH, BYTE PTR [ECX + EAX]
    mov  AX, DX
    // store the last two bytes of the destination quadruple
    STOSW
    dec  ByThrees
  jnz  @@LoopStart
  @@LeftOver:
  // there are up to two more bytes to encode
  cmp  LeftOver, 0
  jz   @@Done
  // clear result
  xor  EAX, EAX
  xor  EBX, EBX
  xor  EDX, EDX
  // get left over 1
  LODSB
  // load the first six bits
  shl  AX, 6
  mov  BL, AH
  // save them
  mov  DL, BYTE PTR [ECX + EBX]
  // another byte ?
  dec  LeftOver
  jz   @@SaveOne
  // save remaining two bits
  shl  AX, 2
  and  AH, $03
  // get left over 2
  LODSB
  // load next 4 bits
  shl  AX, 4
  mov  BL, AH
  // save all 6 bits
  mov  DH, BYTE PTR [ECX + EBX]
  shl  EDX, 16
  // save last 4 bits
  shr  AL, 2
  mov  BL, AL
  // save them
  mov  DL, BYTE PTR [ECX + EBX]
  // load base 64 'no more data flag'
  mov  DH, Base64Filler
  jmp  @@WriteLast4
  @@SaveOne:
  // adjust the last two bits
  shr  AL, 2
  mov  BL, AL
  // save them
  mov  DH, BYTE PTR [ECX + EBX]
  shl  EDX, 16
  // load base 64 'no more data flags'
  mov  DH, Base64Filler
  mov  DL, Base64Filler
  // ignore jump, as jump reference is next line !
  // jmp  @@WriteLast4
  @@WriteLast4:
    // load and adjust result
    mov  EAX, EDX
    ror EAX, 16
    // save it to destination
    STOSD
  @@Done:
end;

{$IFDEF SpeedDecode}

procedure Base64Decode(const InBuffer; InSize: Cardinal; var OutBuffer);
  overload; register;
{$ENDIF}
{$IFDEF ValidityCheck}
  function Base64Decode(const InBuffer; InSize: Cardinal; var OutBuffer):
      Boolean; overload; register;
  {$ENDIF}
  const
  {$IFDEF SpeedDecode}
    cBase64Codec: array[0..127] of Byte =
  {$ENDIF}
  {$IFDEF ValidityCheck}
    cBase64Codec: array[0..255] of Byte =
  {$ENDIF}
    (
      $FF, $FF, $FF, $FF, $FF, {005>} $FF, $FF, $FF, $FF, $FF, // 000..009
      $FF, $FF, $FF, $FF, $FF, {015>} $FF, $FF, $FF, $FF, $FF, // 010..019
      $FF, $FF, $FF, $FF, $FF, {025>} $FF, $FF, $FF, $FF, $FF, // 020..029
      $FF, $FF, $FF, $FF, $FF, {035>} $FF, $FF, $FF, $FF, $FF, // 030..039
      $FF, $FF, $FF, $3E, $FF, {045>} $FF, $FF, $3F, $34, $35, // 040..049
      $36, $37, $38, $39, $3A, {055>} $3B, $3C, $3D, $FF, $FF, // 050..059
      $FF, $FF, $FF, $FF, $FF, {065>} $00, $01, $02, $03, $04, // 060..069
      $05, $06, $07, $08, $09, {075>} $0A, $0B, $0C, $0D, $0E, // 070..079
      $0F, $10, $11, $12, $13, {085>} $14, $15, $16, $17, $18, // 080..089
      $19, $FF, $FF, $FF, $FF, {095>} $FF, $FF, $1A, $1B, $1C, // 090..099
      $1D, $1E, $1F, $20, $21, {105>} $22, $23, $24, $25, $26, // 100..109
      $27, $28, $29, $2A, $2B, {115>} $2C, $2D, $2E, $2F, $30, // 110..119
      $31, $32, $33, $FF, $FF, {125>} $FF, $FF, $FF // 120..127

  {$IFDEF ValidityCheck}
      {125>}, $FF, $FF, // 128..129
      $FF, $FF, $FF, $FF, $FF, {135>} $FF, $FF, $FF, $FF, $FF, // 130..139
      $FF, $FF, $FF, $FF, $FF, {145>} $FF, $FF, $FF, $FF, $FF, // 140..149
      $FF, $FF, $FF, $FF, $FF, {155>} $FF, $FF, $FF, $FF, $FF, // 150..159
      $FF, $FF, $FF, $FF, $FF, {165>} $FF, $FF, $FF, $FF, $FF, // 160..169
      $FF, $FF, $FF, $FF, $FF, {175>} $FF, $FF, $FF, $FF, $FF, // 170..179
      $FF, $FF, $FF, $FF, $FF, {185>} $FF, $FF, $FF, $FF, $FF, // 180..189
      $FF, $FF, $FF, $FF, $FF, {195>} $FF, $FF, $FF, $FF, $FF, // 190..199
      $FF, $FF, $FF, $FF, $FF, {205>} $FF, $FF, $FF, $FF, $FF, // 200..209
      $FF, $FF, $FF, $FF, $FF, {215>} $FF, $FF, $FF, $FF, $FF, // 210..219
      $FF, $FF, $FF, $FF, $FF, {225>} $FF, $FF, $FF, $FF, $FF, // 220..229
      $FF, $FF, $FF, $FF, $FF, {235>} $FF, $FF, $FF, $FF, $FF, // 230..239
      $FF, $FF, $FF, $FF, $FF, {245>} $FF, $FF, $FF, $FF, $FF, // 240..249
      $FF, $FF, $FF, $FF, $FF, {255>} $FF // 250..255
  {$ENDIF}
      );
  asm
  push EBX
  mov  ESI, [EAX]
  mov  EDI, [ECX]
  {$IFDEF ValidityCheck}
    mov  EAX, InSize
    and  EAX, $03
    cmp  EAX, $00
    jz   @@DecodeStart
    jmp  @@ErrorDone
    @@DecodeStart:
  {$ENDIF}
  mov  EAX, InSize
  shr  EAX, 2
  jz   @@Done
  lea  ECX, cBase64Codec[0]
  xor  EBX, EBX
  dec  EAX
  jz   @@LeftOver
  push EBP
  mov  EBP, EAX
  @@LoopStart:
    // load four bytes into EAX
    LODSD
    // save them to EDX as AX is used to store results
    mov  EDX, EAX
    // get bits 0..5
    mov  BL, DL
    // decode
    mov  AH, BYTE PTR [ECX + EBX]
    {$IFDEF ValidityCheck}
      // check valid code
      cmp  AH, $FF
      jz   @@ErrorDoneAndPopEBP
    {$ENDIF}
    // get bits 6..11
    mov  BL, DH
    // decode
    mov  AL, BYTE PTR [ECX + EBX]
    {$IFDEF ValidityCheck}
      // check valid code
      cmp  AL, $FF
      jz   @@ErrorDoneAndPopEBP
    {$ENDIF}
    // align last 6 bits
    shl  AL, 2
    // get first 8 bits
    ror  AX, 6
    // store first byte
    STOSB
    // align remaining 4 bits
    shr  AX, 12
    // get next two bytes from source quad
    shr  EDX, 16
    // load bits 12..17
    mov  BL, DL
    // decode
    mov  AH, BYTE PTR [ECX + EBX]
    {$IFDEF ValidityCheck}
      // check valid code
      cmp  AH, $FF
      jz   @@ErrorDoneAndPopEBP
    {$ENDIF}
    // align ...
    shl  AH, 2
    // ... and adjust
    rol  AX, 4
    // get last bits 18..23
    mov  BL, DH
    // decord
    mov  BL, BYTE PTR [ECX + EBX]
    {$IFDEF ValidityCheck}
      // check valid code
      cmp  BL, $FF
      jz   @@ErrorDoneAndPopEBP
    {$ENDIF}
    // enter in destination word
    or   AH, BL
    // and store to destination
    STOSW
    // more coming ?
    dec  EBP
  jnz  @@LoopStart
  pop  EBP
  // no
  // last four bytes are handled separately, as special checking is needed
  // on the last two bytes (may be end of data signals '=' or '==')
  @@LeftOver:
  // get the last four bytes
  LODSD
  // save them to EDX as AX is used to store results
  mov  EDX, EAX
  // get bits 0..5
  mov  BL, DL
  // decode
  mov  AH, BYTE PTR [ECX + EBX]
  {$IFDEF ValidityCheck}
    // check valid code
    cmp  AH, $FF
    jz   @@ErrorDone
  {$ENDIF}
  // get bits 6..11
  mov  BL, DH
  // decode
  mov  AL, BYTE PTR [ECX + EBX]
  {$IFDEF ValidityCheck}
    // check valid code
    cmp  AL, $FF
    jz   @@ErrorDone
  {$ENDIF}
  // align last 6 bits
  shl  AL, 2
  // get first 8 bits
  ror  AX, 6
  // store first byte
  STOSB
  // get next two bytes from source quad
  shr  EDX, 16
  // check DL for "end of data signal"
  cmp  DL, Base64Filler
  jz   @@SuccessDone
  // align remaining 4 bits
  shr  AX, 12
  // load bits 12..17
  mov  BL, DL
  // decode
  mov  AH, BYTE PTR [ECX + EBX]
  {$IFDEF ValidityCheck}
    // check valid code
    cmp  AH, $FF
    jz   @@ErrorDone
  {$ENDIF}
  // align ...
  shl  AH, 2
  // ... and adjust
  rol  AX, 4
  // store second byte
  STOSB
  // check DH for "end of data signal"
  cmp  DH, Base64Filler
  jz   @@SuccessDone
  // get last bits 18..23
  mov  BL, DH
  // decord
  mov  BL, BYTE PTR [ECX + EBX]
  {$IFDEF ValidityCheck}
    // check valid code
    cmp  BL, $FF
    jz   @@ErrorDone
  {$ENDIF}
  // enter in destination word
  or   AH, BL
  // AH - AL for saving last byte
  mov  AL, AH
  // store third byte
  STOSB
  @@SuccessDone:
  {$IFDEF ValidityCheck}
    mov  Result, $01
    jmp  @@Done
    @@ErrorDoneAndPopEBP:
    pop  EBP
    @@ErrorDone:
    mov  Result, $00
  {$ENDIF}
  @@Done:
  pop  EBX
  end;

  procedure Base64Encode(const InText: PAnsiChar; var OutText: PAnsiChar);
  var
    InSize, OutSize: Cardinal;
  begin
    // get size of source
    InSize := Length(InText);
    // calculate size for destination
    OutSize := CalcEncodedSize(InSize);
    // reserve memory
    OutText := StrAlloc(Succ(OutSize));
    OutText[OutSize] := #0;
    // encode !
    Base64Encode(InText, InSize, OutText);
  end;

  procedure Base64Encode(const InText: AnsiString; var OutText: AnsiString);
    overload;
  var
    InSize, OutSize: Cardinal;
    PIn, POut: Pointer;
  begin
    // get size of source
    InSize := Length(InText);
    // calculate size for destination
    OutSize := CalcEncodedSize(InSize);
    // prepare string length to fit result data
    SetLength(OutText, OutSize);
    PIn := @InText[1];
    POut := @OutText[1];
    // encode !
    Base64Encode(PIn, InSize, POut);
  end;

  procedure Base64Decode(const InText: PAnsiChar; var OutText: PAnsiChar);
    overload;
  var
    InSize, OutSize: Cardinal;
  begin
    // get size of source
    InSize := Length(InText);
    // calculate size for destination
    OutSize := CalcDecodedSize(InText, InSize);
    // reserve memory
    OutText := StrAlloc(Succ(OutSize));
    OutText[OutSize] := #0;
    // encode !
{$IFDEF SpeedDecode}
    Base64Decode(InText, InSize, OutText);
{$ENDIF}
{$IFDEF ValidityCheck}
    if not Base64Decode(InText, InSize, OutText) then
      OutText[0] := #0;
{$ENDIF}
  end;

  procedure Base64Decode(const InText: AnsiString; var OutText: AnsiString);
    overload;
  var
    InSize, OutSize: Cardinal;
    PIn, POut: Pointer;
  begin
    // get size of source
    InSize := Length(InText);
    // calculate size for destination
    PIn := @InText[1];
    OutSize := CalcDecodedSize(PIn, InSize);
    // prepare string length to fit result data
    SetLength(OutText, OutSize);
    FillChar(OutText[1], OutSize, '.');
    POut := @OutText[1];
    // encode !
{$IFDEF SpeedDecode}
    Base64Decode(PIn, InSize, POut);
{$ENDIF}
{$IFDEF ValidityCheck}
    if not Base64Decode(PIn, InSize, POut) then
      SetLength(OutText, 0);
{$ENDIF}
  end;

end.