Passwortsicherheit

[sakura]

Dieser Code wurde uns von Hagen ("negaH") zur Verfügung gestellt und sollte natürlich sofort in die CodeLibrary.

Die vollen Informationen können folgendem Thread entnommen werden: Passwort auf Sicherheit prüfen.

Delphi-Quellcode:

function PassphraseQuality(const Password: String): Extended; 
// returns computed Quality in range 0.0 to 1.0 
// source extracted from Delphi Encryption Compendium, DEC 

  function Entropy(P: PByteArray; L: Integer): Extended; 
  var 
    Freq: Extended; 
    I: Integer; 
    Accu: array[Byte] of LongWord; 
  begin 
    Result := 0.0; 
    if L <= 0 then Exit; 
    FillChar(Accu, SizeOf(Accu), 0); 
    for I := 0 to L-1 do Inc(Accu[P[I]]); 
    for I := 0 to 255 do 
      if Accu[I] <> 0 then 
      begin 
        Freq := Accu[I] / L; 
        Result := Result - Freq * (Ln(Freq) / Ln(2)); 
      end; 
  end; 

  function Differency: Extended; 
  var 
    S: String; 
    L,I: Integer; 
  begin 
    Result := 0.0; 
    L := Length(Password); 
    if L <= 1 then Exit; 
    SetLength(S, L-1); 
    for I := 2 to L do 
      Byte(S[I-1]) := Byte(Password[I-1]) - Byte(Password[I]); 
    Result := Entropy(Pointer(S), Length(S)); 
  end; 

  function KeyDiff: Extended; 
  const 
    Table = '^1234567890ß´qwertzuiopü+asdfghjklöä#<yxcvbnm,.-°!"§$%&/()=?`QWERTZUIOPÜ*ASDFGHJKLÖÄ''>YXCVBNM;:_'; 
  var 
    S: String; 
    L,I,J: Integer; 
  begin 
    Result := 0.0; 
    L := Length(Password); 
    if L <= 1 then Exit; 
    S := Password; 
    UniqueString(S); 
    for I := 1 to L do 
    begin 
      J := Pos(S[I], Table); 
      if J > 0 then S[I] := Char(J); 
    end; 
    for I := 2 to L do 
      Byte(S[I-1]) := Byte(S[I-1]) - Byte(S[I]); 
    Result := Entropy(Pointer(S), L-1); 
  end; 

const 
  GoodLength = 10.0; // good length of Passphrases 
var 
  L: Extended; 
begin 
  Result := Entropy(Pointer(Password), Length(Password)); 
  if Result <> 0 then 
  begin 
    Result := Result * (Ln(Length(Password)) / Ln(GoodLength)); 
    L := KeyDiff + Differency; 
    if L <> 0 then L := L / 64; 
    Result := Result * L; 
    if Result < 0 then Result := -Result; 
    if Result > 1 then Result := 1; 
  end; 
end;

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