Generate random password in Delphi - delphi

Question

I have a following function to generate random passwords:
function GeneratePassword(ALength: Integer; Mode: TPasswordMode): string;
const
cLower = 'abcdefghijklmnopqrstuvwxyz';
cUpper = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
cNumbers = '0123456789';
cExtra = '_.';
var
i : Integer;
S : string;
iM: BYTE;
begin
if Mode = [] then Exit;
i := 0;
Randomize;
while (i < ALength) do
begin
iM := RANDOM(4);
case iM of
0: if (pmLower in Mode) then begin
S := S + cLower[1+RANDOM(Length(cLower))];
Inc(i);
end;
1: if (pmUpper in Mode) then begin
S := S + cUpper[1+RANDOM(Length(cUpper))];
Inc(i);
end;
2: if (pmNumbers in Mode) then begin
S := S + cNumbers[1+RANDOM(Length(cNumbers))];
Inc(i);
end;
3: if (pmExtra in Mode) then begin
S := S + cExtra[1+RANDOM(Length(cExtra))];
Inc(i);
end;
end;
end;
Result := S;
end;
How to make this function so that a capital letter and a special character appear only once, but always? Sometimes there is no capital letter or special character when I'm generating passwords.

Answer 1

To be sure to have one special char and one uppercase you can do that :
function GeneratePassword(ALength: Integer; Mode: TPasswordModes): string;
const
cLower = 'abcdefghijklmnopqrstuvwxyz';
cUpper = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
cNumbers = '0123456789';
cExtra = '_.';
var
iM: Byte;
i: integer;
begin
if Mode = [] then Exit;
Result := '';
i := 0;
if pmUpper in Mode then
Inc(i);
if pmExtra in Mode then
Inc(i);
// add lower case and/or number
while Result.Length < (ALength - i) do
begin
iM := Random(2);
case iM of
0: if (pmLower in Mode) then begin
Result := Result + cLower[1 + Random(Length(cLower))];
end;
1: if (pmNumbers in Mode) then begin
Result := Result + cNumbers[1 + Random(Length(cNumbers))];
end;
end;
end;
// add uppercase and/or extra
if i > 0 then
begin
if pmUpper in Mode then
Result := Result.Insert(1 + Random(Length(Result)), cUpper[1 + Random(Length(cUpper))]);
if pmExtra in Mode then
Result := Result.Insert(1 + Random(Length(Result)), cExtra[1 + Random(Length(cExtra))]);
end;
end;

Answer 2

type
TPasswordMode = (pmLower, pmUpper, pmNumbers, pmExtra);
TPasswordModes = set of TPasswordMode;
implementation
function GeneratePassword(ALength: Integer; Mode: TPasswordModes): string;
const
cLower = 'abcdefghijklmnopqrstuvwxyz';
cUpper = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
cNumbers = '0123456789';
cExtra = '_.';
var
i : Integer;
S : string;
iM: BYTE;
begin
if Mode = [] then Exit;
i := 0;
Randomize;
while (i < ALength) do
begin
iM := RANDOM(4);
case iM of
0: if (pmLower in Mode) then begin
S := S + cLower[1+RANDOM(Length(cLower))];
Inc(i);
end;
1: if (pmUpper in Mode) then begin
S := S + cUpper[1+RANDOM(Length(cUpper))];
Inc(i);
Mode := Mode - [pmUpper]; // This I added
end;
2: if (pmNumbers in Mode) then begin
S := S + cNumbers[1+RANDOM(Length(cNumbers))];
Inc(i);
end;
3: if (pmExtra in Mode) then begin
S := S + cExtra[1+RANDOM(Length(cExtra))];
Inc(i);
Mode := Mode - [pmExtra]; // This I added
end;
end;
end;
Result := S;
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
ShowMessage(GeneratePassword(10,[pmLower,pmUpper,pmNumbers,pmExtra]));
end;
This is not a complete solution but with this you will at least remove Upper and Extra from the requirements as soon as they get taken. You now check in the end if they ever were ever added if required and then add them if so required.
Edit:
I was in a hurry when I typed the above. You just need to check in the end if the generated password contains an Upper and Extra character. If not, you still need to add them as that was one of your requirements.

Answer 3

Here is example that first makes sure all extra modes are filled and the rest. It prefills Result with spaces and then replaces with random chars until all spaces are replaced.
function GetRandomEmptyPos(const aStr: string): integer; inline;
begin
// find random empty position
repeat
Result := Random(Length(aStr)) + 1;
until aStr[Result] = ' ';
end;
function GeneratePassword2(aLength: Integer; aModes: TPasswordModes): string;
const
cLower = 'abcdefghijklmnopqrstuvwxyz';
cUpper = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
cNumbers = '0123456789';
cExtra = '_.';
var
i,vPos: integer;
vMode: TPasswordMode;
begin
if (aLength = 0) or (aModes = []) then Exit;
Randomize;
// Prefill Result with empty spaces
Result := StringOfChar(' ', aLength);
// Add extra characters at random places
for vMode in aModes do
begin
vPos := GetRandomEmptyPos(Result);
case vMode of
pmLower: Result[vPos] := cLower[Random(Length(cLower)) + 1];
pmUpper: Result[vPos] := cUpper[Random(Length(cUpper)) + 1];
pmNumbers: Result[vPos] := cNumbers[Random(Length(cNumbers)) + 1];
pmExtra: Result[vPos] := cExtra[Random(Length(cExtra)) + 1];
end;
end;
// Add random char on emtpy spaces
for i := 1 to Result.Length do
if Result[i] = ' ' then
Result[i] := String(cLower + cNumbers)[Random(Length(cLower) + Length(cNumbers)) + 1];
end;

Answer 4

unrefined code but maybe it can be useful ...
function RandomPassword(PLen: Integer): string;
var
strBase: string;
strUpper: string;
strSpecial: string;
strRecombine: string;
begin
strRecombine:='';
Result := '';
Randomize;
//string with all possible chars
strBase := 'abcdefghijklmnopqrstuvwxyz1234567890';
strUpper:='ABCDEFGHIJKLMNOPQRSTUVWXYZ';
strSpecial:='#!_';
// Start Random
strRecombine:= strUpper[Random(Length(strUpper)) + 1];
Result:=strRecombine;
strRecombine:= strSpecial[Random(Length(strSpecial))+1];
repeat
Result := Result + strBase[Random(Length(strBase)) + 1];
until (Length(Result) = PLen);
RandomRange(2, Length(strBase));
Result[RandomRange(2, PLen)]:=strRecombine[1];
//result:=Result+strRecombine;
end;