Category: Tech Lab

Techincal materials related to electronics, hi-tech gadgets, computer programming and misc. experiments.

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The inverted pyramid puzzle

The other day, I was talking to a friend of mine about the Z3 theorem solver and he mentioned the inverted Pyramid puzzle. I told him: “I think this can be solved with Z3” and hence this blog post.

So what’s the inverted pyramid puzzle?

Imagine the following pyramid with 4 rows:

 10   9   8   7
    6   5   4
      3   2
        1

The numbers in that triangle are just placeholders for the sake of explanation.
The goal of the puzzle is to find the right order for those numbers in the triangle in such a way that:

For the 4th row, we must have whatever is at the position denoted with [number] subtracted from its neighbor equals the value of the next row’s value beneath the top 2 numbers (note: we take the absolute value of the subtraction). So:

|[10] - [9]| == [6]
|[9] - [8] | == [5]
|[8] - [7] | == [4]

And for the 3rd row, we must have:

|[6] - [5]| == [3]
|[5] - [4]| == [2]

And for the 2nd row, we must have:

|[3] - [2]| == [1]

Of course, we stop at the first row.

For now, here’s a solution for the inverted pyramid with 4 rows:

 8 10  3  9
  2  7  6
   5  1
    4

The numbers configuration from above satisfies the conditions explained above.

Please note that the only numbers accepted in the pyramid are [1..Sigma(rows)]. Sigma denotes the sum of the arithmetic series going from 1 to rows. Continue reading “The inverted pyramid puzzle”

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A walkthrough to deobfuscating a ConfuserEx v1.0.0-4 g3fd0d55 protected .NET application

In this blog post, I will show you how to deobfuscated a ConfuserEx protected .NET application.

Unfortunately, there is a lot of videos on YouTube about how to deobfuscate such programs but these videos are so complicated and the instructions are either convoluted or do not yield a good result.

Let’s get started.

Step 1 – Inspecting the binary

You will need to get the dnSpy tool from here: https://github.com/0xd4d/dnSpy/releases

Open the program with dnSpy (or drag and drop it):

At first inspection, we can tell there’s obfuscation due to the name of the entrypoint at line 4 (being so cryptic). Additionally, if you click on the “ConfusedTest.exe” node, you will see more attributes and the obfuscator name (ConfuserEx v1.0.0-4-g3fd0d55):

Continue reading “A walkthrough to deobfuscating a ConfuserEx v1.0.0-4 g3fd0d55 protected .NET application”

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BOSE: Noise masking sleepbuds

I bought myself the noise masking sleepbuds from BOSE to combat loisy upstairs neighbors who stomp all the time at night and early morning:

I tried them for two nights and I like the technology, unfortunately, I did not keep them because they were not comfortable for side sleepers.

The sleepbuds fit well in the ear and produce soothing music (you have a big selection from the phone app), however I found that any external speakers that can generate white noise can do the same effect.


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15 Useful Batch files programming recipes

In the Batchography book, I cover basic to advanced Batch files programming topics. Since the book was published in 2016, I kept blogging about Batch programming language.

Here’s a collection of some useful recipes:

  1. Check if the script is running as an Administrator
  2. String substitution
  3. Number counting
  4. Batch files and Unicode
  5. Read from a text file, one line at a time
  6. Switch/case in Batch files
  7. Auto reinterpret/compile changed files
  8. Reading from a file
  9. Tokenizing command output
  10. Polyglot: Python and Batch files
  11. Polyglot: Batch file + self compiling C++
  12. Embedding binaries inside Batch files
  13. Interactive Batch files
  14. Writing a game – The Hangman
  15. Batchography: Parsing INI files from a Batch file

 

flower separator
batchography-good-resDo you want to master Batch Files programming? Look no further, the Batchography is the right book for you.

Available in print or e-book editions from Amazon.

flower separator


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Can you solve this puzzle?

I got this silly puzzle via chain mail:

Can you solve it?

Maybe you will be able to, but don’t beat yourself up if you don’t get it right.

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When it comes to keyboards, I am super picky!

When I got my first computer, I got attached to its keyboard (The Honeywell 101WN model). In fact, I kept the keyboard until I bought a new computer with no PS/2 ports on it.

It was a sad moment when I realized that I have to move on and find a new keyboard.

While I could have bought a PS/2 adapter, I needed the “Windows” key which is available on newer keyboards.

I think a big majority of programmers love their keyboards and their layout, just like me.

I am very picky when it comes to keyboards. If I don’t like the keyboard, I might not like the whole laptop for instance.

It took me a while to get used to the old MacBook Pro’s keyboards but just after I started liking their keyboards, Apple changed the mechanism to the butterfly mechanism and made the keyboards repulsing in my opinion. I won’t buy a new MacBook because of their keyboards. The same goes for Microsoft Surface laptops. I did not like their toy-like keyboards and therefore won’t buy, endorse or use a Microsoft Surface book or laptop . The most pleasant keyboards so far are the IBM / Lenovo keyboards. That’s why all of my PC laptops are a Lenovo X or T series.

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Batchography: Detect Windows Language

To detect the Windows Operating system language, it is enough to query the registry. We use the “reg query” command and then parse the output.

@echo off

setlocal

:: https://docs.microsoft.com/en-us/previous-versions/office/developer/speech-technologies/hh361638(v=office.14)

for /F "usebackq tokens=3" %%a IN (`reg query "hklm\system\controlset001\control\nls\language" /v Installlanguage`) DO (
  set lang_id=%%a
)
:: 0409 English ; 0407 German ; 040C French ; 0C0A Spanish

if "%lang_id%"=="0409" (
  echo English detected
) else if "%lang_id%" == "040C" (
  echo French detected
) else (
  echo Note: Unknown language ID %lang_id%!
)

echo LangID=%lang_id%

You can learn about advanced Batch scripting techniques in the Batchography book.
flower separator
batchography-good-resDo you want to master Batch Files programming? Look no further, the Batchography is the best book on the topic and the most up to date!

Available in print or e-book editions from Amazon.

 


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Batchography: what happens when you redirect ‘cls’ to a file?

Let’s assume you have a Batch file (test.bat) with the following contents:

@echo off
echo 1
cls
echo 2

And then you run this Batch file and redirect its output to a text file called “out.txt”:

C:>test.bat >out.txt

What do you think the output would be?

At first, I thought it would be:

1
2

But little did I know that when ‘cls’ is invoked in a context where stdout is redirect to a file, then a form feed character (0xC) is emitted instead:

I was curious, so I disassembled ‘cmd.exe’ to verify my findings. Lo and behold, indeed, ‘cmd.exe’ does that:

int __stdcall eCls(struct cmdnode *a1)
{
  HANDLE hStdOut;
  HANDLE v2;
  SMALL_RECT ScrollRectangle; 
  COORD dwDestinationOrigin;
  CHAR_INFO Fill;
  struct _CONSOLE_SCREEN_BUFFER_INFO ConsoleScreenBufferInfo;

  if ( FileIsDevice((char *)1) )
  {
    hStdOut = GetStdHandle(STD_OUTPUT_HANDLE);
    if ( GetConsoleScreenBufferInfo(hStdOut, &ConsoleScreenBufferInfo) )
    {
      dwDestinationOrigin.Y = -ConsoleScreenBufferInfo.dwSize.Y;
      dwDestinationOrigin.X = 0;
      *(_DWORD *)&ScrollRectangle.Left = 0;
      ScrollRectangle.Bottom = ConsoleScreenBufferInfo.dwSize.Y;
      ScrollRectangle.Right = ConsoleScreenBufferInfo.dwSize.X;
      Fill.Char.UnicodeChar = 32;
      Fill.Attributes = ConsoleScreenBufferInfo.wAttributes;
      ScrollConsoleScreenBufferW(hStdOut, &ScrollRectangle, 0, dwDestinationOrigin, &Fill);
      ConsoleScreenBufferInfo.dwCursorPosition = 0;
      v2 = GetStdHandle(0xFFFFFFF5);
      SetConsoleCursorPosition(v2, 0);
    }
    else
    {
      cmd_printf(page_feed);
    }
  }
  else
  {
    cmd_printf(page_feed);
  }
  return 0;
}

(Lines 29 and 34 are of interest)

In conclusion, be aware if you redirect a Batch file to another file and compare the result. If the Batch file uses CLS, you have to account for the form feed character showing up!
flower separator
batchography-good-resDo you want to master Batch Files programming? Look no further, the Batchography is the best book on the topic and the most up to date!

Available in print or e-book editions from Amazon.

 


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Apple’s Measure App

If you have iOS 12+ then you should try Apple’s Measure app. It is really handy.

You can measure:

  • Bookshelves
  • Picture frames
  • Window sizes
  • Door sizes
  • etc…


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Riddle: How many brothers and sisters are there in this family? Z3 Theorem prover

The other day, I ran into a riddle:

A brother said to his sister: “I have as many sisters as brothers”
His sister replied: “I have twice as many brothers as I have sisters”

How many brothers and sisters exist in this family?

I figured that it’s a nice exercise for the Z3 theorem prover. All I had to do is express the riddle in a series of constraints and ask Z3 to try to find a solution.

The following is a Z3Py program that expresses the riddle:

import z3

# Create a solver instance
s = z3.Solver()

# Create two variables representing the total number of males and females (m and f)
m, f = z3.Ints('m f')

# The brother said: I have as many brothers as sisters
s.add(m - 1 == f)

# The sister said: I have twice as much brothers as I have sisters
s.add(2 * (f - 1) == m)

# Check for the solution
if s.check() == z3.sat:
  sol = s.model()
  print "Brothers: %d, Sisters: %d" % (sol[m].as_long(), sol[f].as_long())

When we run the solver, we get the following solution: 4 males, 3 females.

If you prefer the good old systems of equations, we can solve it like this:

The brother said:
m - 1 = f          (1)

The sister said:
2 * (f - 1) = m    (2)


So we have 2 equations, let's do some substitution:

-> f = m - 1        (1)
-> 2f - 2 = m       (2)

--> m = 2f - 2      (2)
--> f = 2f - 2 - 1  (1)
--> f = 2f - 3
--> f - 2f = -3
--> -f = -3
--> f = 3

--> m = 2f - 2
--> m = 2*3 - 2
--> m = 6 - 2
--> m = 4

 

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Batchography: Batch script to automatically recompile or run a script interpreter

Hello,

In a previous blog post, I showed you how to write a polyglot Batch file that is both a Batch script and a C++ source file. When the Batch file is executed, it compiles itself (as C++).  In this blog post I am going to show you how to write a Batch file script that polls the file system periodically to see if a given input file is changed and if so, it will invoke the compiler or interpreter of your choice.

This concept is similar to what the Compiler Explorer does actually.

I am going to write a small script that keeps running your Python script automatically in a separate console window the moment you save the script in your editor. Check the script in action:

Continue reading “Batchography: Batch script to automatically recompile or run a script interpreter”