Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

const
   Codes64 = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz+/';

 function Encode64(S: string): string;
 var
   i: Integer;
   a: Integer;
   x: Integer;
   b: Integer;
 begin
   Result := '';
   a := 0;
   b := 0;
   for i := 1 to Length(s) do
   begin
     x := Ord(s[i]);
     b := b * 256 + x;
     a := a + 8;
     while a >= 6 do
     begin
       a := a - 6;
       x := b div (1 shl a);
       b := b mod (1 shl a);
       Result := Result + Codes64[x + 1];
     end;
   end;
   if a > 0 then
   begin
     x := b shl (6 - a);
     Result := Result + Codes64[x + 1];
   end;
 end;

 function Decode64(S: string): string;
 var
   i: Integer;
   a: Integer;
   x: Integer;
   b: Integer;
 begin
   Result := '';
   a := 0;
   b := 0;
   for i := 1 to Length(s) do
   begin
     x := Pos(s[i], codes64) - 1;
     if x >= 0 then
     begin
       b := b * 64 + x;
       a := a + 6;
       if a >= 8 then
       begin
         a := a - 8;
         x := b shr a;
         b := b mod (1 shl a);
         x := x mod 256;
         Result := Result + chr(x);
       end;
     end
     else
       Exit;
   end;
 end;