Passwort-Stärke ermitteln (Code und Prüflogik)

[Satty67]

...und bei PassphraseQuality? und bei der verfeinerten Funktion in TPasswortCheck?

Ich erspare mir alle genannten Beispiele mit den Alternativen zu vergleichen. Wer ernsthaft vergleichen will, kann es selber machen. Wie gesagt, eine perfekte Funktion kann es nicht geben, zuviele Fallen.

Hier die entgültige Methode, wie sie im Forum in TPasswortCheck vorgestellt wurde. (Nur schnell wieder aus der Komponente rausgeschnippelt, kein Schönheitspreis erwartet )

Delphi-Quellcode:

unit UPasswordCheckFunktion;

interface

function GetPasswordStrength(Password: String; ForceEntropy : Boolean = false): Extended;

implementation

uses
  SysUtils, math;

function RemoveRepetitions(const AString : string): String;
var
  i : Integer;
begin
  Result := AString;
  i := 2;
  while i <= Length(Result) do
  begin
    if Result[i] = Result[i-1] then
      Delete(Result, i, 1)
    else
      inc(i);
  end;
end;

function RemoveDateSeparator(const AString : string): String;
var
  i : Integer;
  dt : TDateTime;
begin
  i := Length(AString);
  if (i > 0) and (AString[i] = DateSeparator) then
    Result := Copy(AString, 1, i-1)
  else
    Result := AString;

  if TryStrToDate(Result, dt) then
    Result := StringReplace(AString, DateSeparator, '', [rfReplaceAll]);
end;

function GetPasswordStrength(Password: String; ForceEntropy : Boolean = false): Extended;
var
  FLowerMultiplicator   : Extended;
  FUpperMultiplicator   : Extended;
  FNumericMultiplicator : Extended;
  FSignMultiplicator    : Extended;
  FDiffCharsMaxMulti    : Extended;
  FLengthMultiplicator  : Extended;

  FMinPasswordLength    : Integer;
  FMaxPasswordLength    : Integer;

  procedure InitPasswordCheck(ForceEntropie : Boolean);
  begin
    FLowerMultiplicator   := 19;
    FUpperMultiplicator   := 21;
    FNumericMultiplicator := 15;
    FSignMultiplicator    := 25;
    FDiffCharsMaxMulti    := 100;
    FLengthMultiplicator  := 20;

    FMinPasswordLength    := 4;
    FMaxPasswordLength    := 32;

    if ForceEntropie then
      FDiffCharsMaxMulti := FDiffCharsMaxMulti * 10;
  end;

  function LengthMul(const CurrentLength, MaxLength : Integer): Extended;
  begin
    if CurrentLength > MaxLength then
      Result := Math.Log2(MaxLength) * Math.Log2(MaxLength)
    else
      Result := Math.Log2(CurrentLength) * Math.Log2(CurrentLength);

    Result := Result * FLengthMultiplicator;
  end;

  function CalculateEntropie(CleanPWLength, DiffCharsCount : Integer;
                  LowerMul, UpperMul, NumericMul, SignMul: Extended):Extended;
  begin
    Result := (DiffCharsCount * FDiffCharsMaxMulti) / CleanPWLength;
    if (NumericMul + SignMul) = 0 then
      Result := Result + ((LowerMul + UpperMul) / 2)
    else
      Result := Result + LowerMul + UpperMul + NumericMul + SignMul;
  end;

  function GetBestResult: Extended;
  begin
    Result := CalculateEntropie(1, 1, FLowerMultiplicator, FUpperMultiplicator,
                                FNumericMultiplicator, FSignMultiplicator);
    Result := Result * LengthMul(FMaxPasswordLength, FMaxPasswordLength);
  end;

var
  i, CleanPWLength : Integer;
  CleanPassword,
  DiffChars : String;
  EntropieMul,
  LowerMul, UpperMul,
  NumericMul, SignMul : Extended;
begin
  Result     := 0;

  LowerMul   := 0;
  UpperMul   := 0;
  NumericMul := 0;
  SignMul    := 0;

  InitPasswordCheck(ForceEntropy);
  CleanPassword := Trim(Password);
  CleanPassword := RemoveDateSeparator(CleanPassword);
  CleanPassword := RemoveRepetitions(CleanPassword);

  CleanPWLength := Length(CleanPassword);
  if (CleanPWLength >= FMinPasswordLength) then
  begin

    for i := 1 to Length(CleanPassword) do
    begin
      case CleanPassword[i] of
        'a'..'z', ' ' : LowerMul   := FLowerMultiplicator;
        'A'..'Z' : UpperMul   := FUpperMultiplicator;
        '0'..'9' : NumericMul := FNumericMultiplicator;
      else
        SignMul := FSignMultiplicator;
      end;

      if Pos(CleanPassword[i], DiffChars) < 1 then
        DiffChars := DiffChars + CleanPassword[i];
    end;

    EntropieMul := CalculateEntropie(CleanPWLength, Length(DiffChars),
                                     LowerMul, UpperMul, NumericMul, SignMul);

    Result := EntropieMul * LengthMul(CleanPWLength, FMaxPasswordlength);
    Result := Result / GetBestResult;
  end;
end;

end.