Question

I am looking for something more sophisticated than ROT13, but which does not require a library (preferablly not even a unit, just a drop in function).

I want to symetrically encrypt/decrypt a given string with a password provided by the user. However, the result has to be a string, in the sense that it I have to be able to store it in an .INI file.

Does anyone have a simple function to do this (delphi XE2)? Google is not my friend today.

Thanks in advance

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[Update] / [Bounty] Just to make it clear (aplogies if it was not so originally), I don’t want a hash. I have a list box where users can add/modiy/delete entries. I want to store those in an .INI file when the program closes and reload when it starts again. Anyone looking at the .INI file (for instance, opening it in Notepad) should not be able to read those strings.

I suppose that I could just stream the compnent as binary, but for eace of mind I would rather encrypt the strings using a user provided password. For the purpose of this applciation it does not matter if .INI file section names or keyte values are human readable, I just want to encrypt the data, giving me something list this when stored on disk:

[config]
numEntries=3

[listbox]
0=ywevdyuvewfcyuw
1=edw
2=hr4uifareiuf

Answer 1

This is a replacement for Tinifile.
ReadString and WriteString are overridden, these are internal used to for Read/WriteFloat, Read/WriteInteger etc.

Strings are encrypted and stored as HEX-Strings.

Demo usage:

uses CryptingIni;
{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
 ini:TCryptingIni;
begin
    ini:=TCryptingIni.Create('C:\temp\test.ini');
    ini.UseInternalVersion(1234);
    ini.WriteFloat('Sect','Float',123.456);
    ini.WriteString('Sect2','String','How to encode');
    ini.Free;
end;

procedure TForm1.Button2Click(Sender: TObject);
var
 ini:TCryptingIni;
begin
    ini:=TCryptingIni.Create('C:\temp\test.ini');
    ini.UseInternalVersion(1234);
    Showmessage(FloatToStr(ini.ReadFloat('Sect','Float',0)));
    Showmessage(ini.ReadString('Sect2','String',''));
    Showmessage(ini.ReadString('SectUnkknow','Showdefault','DEFAULT'));
    ini.Free;
end;

You may use internal encryption method by UseInternalVersion, or provide own procedures with
Procedure SetCryptingData(aEncryptProc, aDecryptProc: CryptingProc; aKey: Word);

unit CryptingIni;

// 2013 by Thomas Wassermann
interface

uses
  Windows, SysUtils, Variants, Classes, inifiles;

type

  CryptingProc = Function(const InString: String; Key: Word): String;

  TCryptingIni = Class(TInifile)
    function ReadString(const Section, Ident, Default: string): string; override;
    procedure WriteString(const Section, Ident, Value: String); override;
  private
    FEncryptProc: CryptingProc;
    FDecryptProc: CryptingProc;
    FKey: Word;
  public
    Procedure SetCryptingData(aEncryptProc, aDecryptProc: CryptingProc; aKey: Word);
    Procedure UseInternalVersion(aKey: Word);
  End;

implementation

const
  c1 = 52845;
  c2 = 22719;

Type
  TByteArray = Array [0 .. 0] of byte;

Function AsHexString(p: Pointer; cnt: Integer): String;
var
  i: Integer;
begin
  Result := '';
  for i := 0 to cnt do
    Result := Result + '$' + IntToHex(TByteArray(p^)[i], 2);
end;

Procedure MoveHexString2Dest(Dest: Pointer; Const HS: String);
var
  i: Integer;
begin
  i := 1;
  while i < Length(HS) do
  begin
    TByteArray(Dest^)[i div 3] := StrToInt(Copy(HS, i, 3));
    i := i + 3;
  end;
end;

function EncryptV1(const s: string; Key: Word): string;
var
  i: smallint;
  ResultStr: string;
  UCS: WIDEString;
begin
  Result := s;
  if Length(s) > 0 then
  begin
    for i := 1 to (Length(s)) do
    begin
      Result[i] := Char(byte(s[i]) xor (Key shr 8));
      Key := (smallint(Result[i]) + Key) * c1 + c2
    end;
    UCS := Result;
    Result := AsHexString(@UCS[1], Length(UCS) * 2 - 1)
  end;
end;

function DecryptV1(const s: string; Key: Word): string;
var
  i: smallint;
  sb: String;
  UCS: WIDEString;
begin
  if Length(s) > 0 then
  begin
    SetLength(UCS, Length(s) div 3 div 2);
    MoveHexString2Dest(@UCS[1], s);
    sb := UCS;
    SetLength(Result, Length(sb));
    for i := 1 to (Length(sb)) do
    begin
      Result[i] := Char(byte(sb[i]) xor (Key shr 8));
      Key := (smallint(sb[i]) + Key) * c1 + c2
    end;
  end
  else
    Result := s;
end;

{ TCryptingIni }

function TCryptingIni.ReadString(const Section, Ident, Default: string): string;
begin
  if Assigned(FEncryptProc) then
    Result := inherited ReadString(Section, Ident, FEncryptProc(Default, FKey))
  else
    Result := inherited ReadString(Section, Ident, Default);
  if Assigned(FDecryptProc) then
    Result := FDecryptProc(Result, FKey);
end;

procedure TCryptingIni.SetCryptingData(aEncryptProc, aDecryptProc: CryptingProc; aKey: Word);
begin
  FEncryptProc := aEncryptProc;
  FDecryptProc := aDecryptProc;
  FKey := aKey;
end;

procedure TCryptingIni.UseInternalVersion(aKey: Word);
begin
  FKey := aKey;
  FEncryptProc := EncryptV1;
  FDecryptProc := DecryptV1;
end;

procedure TCryptingIni.WriteString(const Section, Ident, Value: String);
var
  s: String;
begin
  if Assigned(FEncryptProc) then
    s := FEncryptProc(Value, FKey)
  else
    s := Value;
  inherited WriteString(Section, Ident, s);
end;

end.