String handling issue with Free Pascal

[Sogcelak]

I don't want to save all possible strings, just the ones that are matching the hash.

To avoid further misunderstanding, I will copy my current code here, and maybe you could tell me what's wrong because just when I thought it would work, it doesn't really. It runs, it's trying out everything, but something is bugged...

Program Md5BruteForce;

Uses Md5;

Var

hash,test,tri:string;

Num,Max,j:integer;

Results: array[1..100] of string;


Function NextChar(c:char):char; //This is for changing the characters in the string

Begin

 if c='z' then NextChar:='0'
 else
 if c='9' then NextChar:='a'
 else
 NextChar:=Succ(c);

End;

Procedure ChangeChar(MaxLength,spot:integer; Var Str:string); //The main procedure

Var

 counter:integer;
 i:integer;

Begin

 counter:=0;


 if Str[spot]='9' then 

 begin

  if length(Str)<=MaxLength then 

  begin

   for i:=1 to length(Str) do
   begin

    if Str[i]='9' then counter:=counter+1; //Count the 9s in the string

   end;

   if counter=length(Str) then
   begin

    for i:=1 to length(Str) do Str[i]:='a'; 
    Str:=Str+'a'; //If every character is a 9, then change all of them back to 'a', and add a plus 'a' to the string
   end

   else
   begin
    Str[spot]:='a';
    ChangeChar(MaxLength, spot-1,Str); //The procedure calls itself, until a non-9 character is found
   end;
  end;
 end
 else

 Str[spot]:=NextChar(Str[spot]); //If a non-9 character is found then it is simply switched to the next character


End;



Begin

for j:=1 to 100 do Results[j]:='' //Clearing the array, just to make sure...

Writeln('Please Give me the hash');
Readln(hash);

Writeln('Please give me the estimated maximum length of the original text(characters)');
Readln(Max);

test:='a';

Num:=1;

Repeat

tri:=MD5Print(Md5String(test));

if tri=hash then

begin

 Results[Num]:=test;
 Num:=Num+1; //Storing the matches in an array

end;

Write('Now trying: ',test);
Write('       ');
Writeln('Hash: ',tri); //A bit redundant, but it helped me debug the recursion, and it looks cool so I kept it.

ChangeChar(Max,length(test),test); //Go to the next variation

Until length(test)>Max; //Loop ends if the maximum character length is exceeded

if Num>1 then //Checking if there is more than 0 results

begin

 for j:=1 to Num do
  begin

  Writeln('Result #',j,': ',Results[Num]); //Writing out all the results
  end;
end
else

Writeln('Sorry, your hash could not be recovered'); //If the search fails...

Readln;

End.

I was testing with the string 'c7' at maximum length 2 and 3. (hash is: 4d3a21d8c684c09c19b93be911827fd5)
The problem is that eventhough it tries every possible permutation now, for some reason it can't list the results. The output is exactly this(except for the long blocks of tries)
'Result #1:
Result #2:'
And that's it. Empty strings. Arrrrgh it's driving me soooo mad, I'm pretty much done with the hard part, and some stupid error is stopping me.

[Sogcelak]

Nevermind, I'm done with it. It was the stupidest error ever.

In the for cycle when I'm writing the results out
Instead of Results[Num] I should use Results[j]

Now the code is fully functional(except for that it takes forever to decode anything beyond 4 character length) Thanks for the input guys.

Program Md5BruteForce;

Uses Md5;

Var

hash,test,tri:string;

Num,Max,j:integer;

Results:array[1..100] of string;


Function NextChar(c:char):char; //This is for changing the characters in the string

Begin

 if c='z' then NextChar:='0'
 else
 if c='9' then NextChar:='a'
 else
 NextChar:=Succ(c); //Succ=Next Character in ABC order, next number if the character is a number

End;

Procedure ChangeChar(MaxLength,spot:integer; Var Str:string); //The main procedure

Var

 counter:integer;
 i:integer;
Begin

 counter:=0;


 if Str[spot]='9' then

 begin

  if length(Str)<=MaxLength then

  begin

   for i:=1 to length(Str) do
   begin

    if Str[i]='9' then counter:=counter+1; //Count the 9s in the string

   end;

   if counter=length(Str) then
   begin

    for i:=1 to length(Str) do Str[i]:='a';
    Str:=Str+'a'; //If every character is a 9, then change all of them back to 'a', and add a plus 'a' to the string

   end

   else
   begin
    Str[spot]:='a';
    ChangeChar(MaxLength, spot-1,Str); //The procedure calls itself, until a non-9 character is found
   end;
  end;
 end
 else

 Str[spot]:=NextChar(Str[spot]); //If a non-9 character is found then it is simply switched to the next character


End;



Begin

for j:=1 to 100 do

begin
 Results[j]:=''; //Clearing the array, just to make sure...
end;

Writeln('Please Give me the hash');
Readln(hash);

Writeln('Please give me the estimated maximum length of the original text(characters)');
Readln(Max);

test:='a';

Num:=1;

Repeat

tri:=MD5Print(Md5String(test));

if tri=hash then

begin
Results[Num]:=test;
Num:=Num+1; //Storing the matches in an array

end;

Write('Now trying: ',test);
Write('       ');
Writeln('Hash: ',tri); //A bit redundant, but it helped me debug the recursion, and it looks cool so I kept it.

ChangeChar(Max,length(test),test); //Go to the next variation

Until length(test)>Max; //Loop ends if the maximum character length is exceeded

if Num>1 then //Checking if there is more than 0 results

begin

 for j:=1 to Num-1 do
  begin

  Writeln('Result #',j,': ',Results[j]); //Writing out all the results

  end;
end
else
Writeln('Sorry, your hash could not be recovered'); //If the search fails...

Readln;

End.

[SilverWarior]

Now why not implement multithreading to make everything run faster

[Sogcelak]

I actually needed to look up how multithreading exactly works in Pascal. And I still don't get half of it, so that will take some time. Keep in mind I've hardly ever used objects in my programs, only simple ones. This TThread class is a mess compaired to them.

I've deleted the part of the program where it writes out every try, now it just outputs the result, and it is a lot faster now. At 5 character length it still seems unexplainably slow(I haven't tried with more). This multithreading seems like something that could work but I need to study it further before I can implement it in my program.

[User137]

If you would want to optimize it a bit, i would first get rid of NextChar() function. You could put all valid characters in a string constant, something like

const validstr = 'abcd....ABCD....XYZ0123456789';

Then matter of changing character is simply increasing character index by 1.

index:=1;
validstr[index] is 'a'
inc(index);
validstr[index] is now 'b'

[AthenaOfDelphi]

I actually needed to look up how multithreading exactly works in Pascal. And I still don't get half of it, so that will take some time. Keep in mind I've hardly ever used objects in my programs, only simple ones. This TThread class is a mess compaired to them.

I've deleted the part of the program where it writes out every try, now it just outputs the result, and it is a lot faster now. At 5 character length it still seems unexplainably slow(I haven't tried with more). This multithreading seems like something that could work but I need to study it further before I can implement it in my program.

I have a tutorial that covers the basics of multi-threading.