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Laszlo
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PostPosted: October 24th, 2007, 10:49 pm 
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Location: Boulder, CO
No, the last script was to demonstrate the fixed bits. You only need the GUID function from first post, and either RandR (for floating point random numbers) or RandI for random integers, also from the first post.


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Leon
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PostPosted: October 24th, 2007, 11:32 pm 
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Posts: 179
@Laszlo
Thanks. I've edited the code to my needs and it seems to be working fine.
I get the following which looks fine
Quote:
ed234b7cc39a849a41be48172e54f014
b13f45c20926a68c4ff9a9babeacc9d5
6234ee6a3b642aa749a6daf082dd45ca
946 1002 980 1051 962 991 1023 978 1049 1018

Could u please check my code below?
The lines commented with ;RandI were commented out as they are not necessary if using RandI instead of RandR - was I correct?
Also is there any advantage of RandR over RandI ?

Code:
;SetFormat float, 4.18               ;RandI

MsgBox % GUID()                     
MsgBox % GUID()
MsgBox % GUID()

;MsgBox % RandR()                    ;RandI           
;MsgBox % RandR()                    ;RandI                 
;MsgBox % RandR()                    ;RandI                   

Loop 10000                         
{
   f := RandI(0,9)                 
   d%f% += 1                       
}
MsgBox %d0%`n%d1%`n%d2%`n%d3%`n%d4%`n%d5%`n%d6%`n%d7%`n%d8%`n%d9%`n


GUID()         
{
   format = %A_FormatInteger%       
   SetFormat Integer, Hex           
   VarSetCapacity(A,16)
   DllCall("rpcrt4\UuidCreate","Str",A)
   Address := &A
   Loop 16
   {
      x := 256 + *Address         
      StringTrimLeft x, x, 3       
      h = %x%%h%                   
      Address++
   }
   SetFormat Integer, %format%     
   Return h
}

RandI(min,max)
{
   VarSetCapacity(A,16)
   DllCall("rpcrt4\UuidCreate","Str",A)
   Address := &A - 1
   r = 0
   Loop 8
      r := (r + (*(Address+A_Index) ^ *(Address+A_Index+8)))/256.0
   Return min + Floor(r*(max-min+1))
}


Thanks for all your help


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Laszlo
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PostPosted: October 24th, 2007, 11:50 pm 
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Joined: February 14th, 2005, 4:05 pm
Posts: 4710
Location: Boulder, CO
In AHK XOR is denoted by the caret symbol
Code:
*(Address+A_Index) ^ *(Address+A_Index+8))
The code takes bytes eight positions apart and XOR them, behind the scenes. The result is used, it has no fixed bits any more. (The result of the last loop tells that in 10,000 random numbers between 0 and 9 there were 946 zeros, 1002 ones, 980 twos…)

The code you posted is OK. RandR and RandI are used for different purposes. If you need random integers, use the later one, if you need floating point random numbers, used the former one.


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Leon
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PostPosted: October 25th, 2007, 12:25 am 
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Joined: August 27th, 2007, 8:00 pm
Posts: 179
Aha! the caret!!

So for the pupose of creating a random number to use as a hash key, I would be better to use RandI, right?


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Laszlo
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PostPosted: October 25th, 2007, 12:56 am 
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Joined: February 14th, 2005, 4:05 pm
Posts: 4710
Location: Boulder, CO
right


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Leon
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PostPosted: October 25th, 2007, 1:07 am 
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Posts: 179
Quote:
(The result of the last loop tells that in 10,000 random numbers between 0 and 9 there were 946 zeros, 1002 ones, 980 twos…)

I guess these could almost be used as extra numbers for hashing.
But they are so similar would it be of any use to do so?


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Laszlo
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PostPosted: October 25th, 2007, 1:56 am 
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Posts: 4710
Location: Boulder, CO
Of course, they are similar: these are the frequencies of random integers. If they are uniformly distributed, they should occur roughly the same number of times. It is actually a randomness test. If the deviation from the mean (1,000) is larger than 3σ (~100), we had a problem. Don’t use these numbers for other purposes: they are slow to generate and should be close together.


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Leon
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PostPosted: October 25th, 2007, 2:19 am 
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Joined: August 27th, 2007, 8:00 pm
Posts: 179
I see.
So if I use the script below to generate a key for the purposes of hashing some unique info,
would it be worth including the randomness test in a such a system, combined with having the script check the difference between values (ie check randomness) and if they are not deemed random enough take alternative action (exit i assume)

Could including it for example, detect user interference (attempted hacking)?
Or are there also possible situations where a such a level of (inadequate) randomness could occur through no malicious intent by User?

Code:
MsgBox % GUID()

GUID()         
{
   format = %A_FormatInteger%       
   SetFormat Integer, Hex           
   VarSetCapacity(A,16)
   DllCall("rpcrt4\UuidCreate","Str",A)
   Address := &A
   Loop 16
   {
      x := 256 + *Address         
      StringTrimLeft x, x, 3       
      h = %x%%h%                   
      Address++
   }
   SetFormat Integer, %format%     
   Return h
}


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Laszlo
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PostPosted: October 25th, 2007, 3:21 am 
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Posts: 4710
Location: Boulder, CO
This test was posted to prove the concept. You don’t need it. Either the GUID’s are good, or you should see an error returned from DllCall(“rpcrt4\UuidCreate”,”Str”,A). Either the ErroLevel or the return value is nonzero, non-empty.

It is possible that an attacker replaces the rpcrt4.dll in the target PC, and generates bad GUID’s. However, if he is not stupid, he would generate random looking ID’s, (something like a truncated multiple of the time), so such a simple randomness test would not catch him, but he has a pretty good idea about the generated number. I would not bother testing the GUID’s, only possible errors, like
Code:
; ...
Result := DllCall(“rpcrt4\UuidCreate”,”Str”,A)
If (result or ErrorLevel)
   MsgBox GUID is not supported
; ...

With “generate a key for the purposes of hashing” you probably mean “a key for the purposes of encrypting”. These GUID’s can be good for crypto keys, but knowing nothing about the algorithm generating them, we cannot be sure. Some physical source of randomness could be safer.


Last edited by Laszlo on October 25th, 2007, 6:18 am, edited 1 time in total.

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Laszlo
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PostPosted: October 25th, 2007, 3:44 am 
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Joined: February 14th, 2005, 4:05 pm
Posts: 4710
Location: Boulder, CO
Btw, for more recent AHK versions we can write the GUID function a little compacter
Code:
GUID() {
   format = %A_FormatInteger%
   SetFormat Integer, Hex
   VarSetCapacity(A,16)
   DllCall("rpcrt4\UuidCreate","Str",A)
   Loop 16
      h .= SubStr(256+NumGet(A,A_Index-1,"UChar"),-1)
   SetFormat Integer, %format%
   Return h
}


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Leon
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PostPosted: October 25th, 2007, 4:00 am 
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Joined: August 27th, 2007, 8:00 pm
Posts: 179
Thanks for the more compact option.
Quote:
With “generate a key for the purposes of hashing” you probably mean “a key for the purposes of encrypting”

Yes I'm not too sure of the terminology there, so to clarify, I would like to use the Processor ID (globally unique and available from any processor as far as I know - correct me if I'm wrong)
and have it "interact" with the GUID in order to "disguise" it so as not to be dealing with people's private info.
By interact, I'm not yet sure what I mean. I guess multiplication?
Although that seems very simple.
Would it be better to use a method like the (K0, K1 etc) keys from your "SW copy protection" thread?


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Leon
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PostPosted: October 25th, 2007, 4:05 am 
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Joined: August 27th, 2007, 8:00 pm
Posts: 179
Laszlo wrote:
I would not bother testing the GUID’s, only possible errors, like
Code:
; ...
Result = DllCall(“rpcrt4\UuidCreate”,”Str”,A)
If (result or ErrorLevel)
   MsgBox GUID is not supported
; ...


So it is possible for that to happen then - for GUIDs to not be supported? (only concerned with XP or later)
If so, do u have any experience / guess as to how likley /frequent that could happen?


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Laszlo
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PostPosted: October 25th, 2007, 4:13 am 
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Joined: February 14th, 2005, 4:05 pm
Posts: 4710
Location: Boulder, CO
I think it would not happen in XP, 2003 or Vista.

...and here is an even shorter version, w/o the likely unnecessary error check:
Code:
GUID() {
   VarSetCapacity(A,16), S := "12"
   DllCall("rpcrt4\UuidCreate","Str",A)
   Loop 16
      DllCall("msvcrt\sprintf", Str,S, Str,"%02x", "Uchar",*(&A+A_Index-1)), h .= S
   Return h
}


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Leon
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PostPosted: October 25th, 2007, 4:40 am 
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Joined: August 27th, 2007, 8:00 pm
Posts: 179
Thanks a lot Laszlo.

As a test i added the error check to the shortest code, but I got "GUID not supported". I have commented the various places i tried adding the error checking code.
Purely so I learn... where I am i wrong here?
Code:
;HERE   

GUID() {
   VarSetCapacity(A,16), S := "12"
   DllCall("rpcrt4\UuidCreate","Str",A)
   Result = DllCall(“rpcrt4\UuidCreate”,”Str”,A)
;HERE
   Loop 16
      DllCall("msvcrt\sprintf", Str,S, Str,"%02x", "Uchar",*(&A+A_Index-1)), h .= S
   Return h
}
MsgBox % GUID()
;HERE


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Laszlo
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PostPosted: October 25th, 2007, 6:20 am 
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Joined: February 14th, 2005, 4:05 pm
Posts: 4710
Location: Boulder, CO
Sorry, there was a typo in the error check. We need ":=", not "=".
Code:
GUID() {
   VarSetCapacity(A,16), S := "12"
   DllCall("rpcrt4\UuidCreate","Str",A)
   Result := DllCall("rpcrt4\UuidCreate","Str",A)
   If (result or ErrorLevel)
      MsgBox % GUID is not supported
   Loop 16
      DllCall("msvcrt\sprintf", Str,S, Str,"%02x", "Uchar",*(&A+A_Index-1)), h .= S
   Return h
}


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