// This example shows how you can encrypt strings 
// using special security string. 
// You can decode data only if you know security string. 
// I suppose, there is no chance to hack security string, using any analyse algorythms. 
// Every time you call this function, you will 
// have a new result even if all params are constant 
// NOTE: Don`t forget to call "Randomize" proc before using this functions. 

const
 Codes64 = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz+/';

 // you must use this function to generate special 
 // security string, which is used in main encode/decode routines. 
 // NOTE: you must generate the security string only once and then use it in encode/decode functions. 

function GeneratePWDSecutityString: string;
 var
 i, x: integer;
 s1, s2: string;
 begin
 s1 := Codes64;
 s2 := '';
 for i := 0 to 15 do
 begin
 x := Random(Length(s1));
 x := Length(s1) - x;
 s2 := s2 + s1[x];
 s1 := Copy(s1, 1,x - 1) + Copy(s1, x + 1,Length(s1));
 end;
 Result := s2;
 end;

 // this function generate random string using 
// any characters from "CHARS" string and length 
// of "COUNT" - it will be used in encode routine 
// to add "noise" into your encoded data. 

function MakeRNDString(Chars: string; Count: Integer): string;
 var
 i, x: integer;
 begin
 Result := '';
 for i := 0 to Count - 1 do
 begin
 x := Length(chars) - Random(Length(chars));
 Result := Result + chars[x];
 chars := Copy(chars, 1,x - 1) + Copy(chars, x + 1,Length(chars));
 end;
 end;


 // This will encode your data. 
// "SecurityString" must be generated using method 
// described above, and then stored anywhere to 
// use it in Decode function. 
// "Data" is your string (you can use any characters here) 
// "MinV" - minimum quantity of "noise" chars before each encoded data char. 
// "MaxV" - maximum quantity of "noise" chars before each encoded data char. 

function EncodePWDEx(Data, SecurityString: string; MinV: Integer = 0;
 MaxV: Integer = 5): string;
 var
 i, x: integer;
 s1, s2, ss: string;
 begin
 if minV > MaxV then
 begin
 i := minv;
 minv := maxv;
 maxv := i;
 end;
 if MinV < 0 then MinV := 0;
 if MaxV > 100 then MaxV := 100;
 Result := '';
 if Length(SecurityString) < 16 then Exit;
 for i := 1 to Length(SecurityString) do
 begin
 s1 := Copy(SecurityString, i + 1,Length(securitystring));
 if Pos(SecurityString[i], s1) > 0 then Exit;
 if Pos(SecurityString[i], Codes64) <= 0 then Exit;
 end;
 s1 := Codes64;
 s2 := '';
 for i := 1 to Length(SecurityString) do
 begin
 x := Pos(SecurityString[i], s1);
 if x > 0 then s1 := Copy(s1, 1,x - 1) + Copy(s1, x + 1,Length(s1));
 end;
 ss := securitystring;
 for i := 1 to Length(Data) do
 begin
 s2 := s2 + ss[Ord(Data[i]) mod 16 + 1];
 ss := Copy(ss, Length(ss), 1) + Copy(ss, 1,Length(ss) - 1);
 s2 := s2 + ss[Ord(Data[i]) div 16 + 1];
 ss := Copy(ss, Length(ss), 1) + Copy(ss, 1,Length(ss) - 1);
 end;
 Result := MakeRNDString(s1, Random(MaxV - MinV) + minV + 1);
 for i := 1 to Length(s2) do Result := Result + s2[i] + MakeRNDString(s1,
 Random(MaxV - MinV) + minV);
 end;

 // This will decode your data, encoded with the function above, using specified "SecurityString". 

function DecodePWDEx(Data, SecurityString: string): string;
 var
 i, x, x2: integer;
 s1, s2, ss: string;
 begin
 Result := #1;
 if Length(SecurityString) < 16 then Exit;
 for i := 1 to Length(SecurityString) do
 begin
 s1 := Copy(SecurityString, i + 1,Length(securitystring));
 if Pos(SecurityString[i], s1) > 0 then Exit;
 if Pos(SecurityString[i], Codes64) <= 0 then Exit;
 end;
 s1 := Codes64;
 s2 := '';
 ss := securitystring;
 for i := 1 to Length(Data) do if Pos(Data[i], ss) > 0 then s2 := s2 + Data[i];
 Data := s2;
 s2 := '';
 if Length(Data) mod 2 <> 0 then Exit;
 for i := 0 to Length(Data) div 2 - 1 do
 begin
 x := Pos(Data[i * 2 + 1], ss) - 1;
 if x < 0 then Exit;
 ss := Copy(ss, Length(ss), 1) + Copy(ss, 1,Length(ss) - 1);
 x2 := Pos(Data[i * 2 + 2], ss) - 1;
 if x2 < 0 then Exit;
 x := x + x2 * 16;
 s2 := s2 + chr(x);
 ss := Copy(ss, Length(ss), 1) + Copy(ss, 1,Length(ss) - 1);
 end;
 Result := s2;
 end;