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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