Clue

Ghost text is … invisible!

ghost_text.txt

Hint

AA_AAA_ = 01001

Approach

The hint on this particular one is really required to figure out the problem. I opened the text file in a hex editor and found that there were extra non-printable characters in the file. My interpretation of the hint is that all non-printable characters were a 1 and for all n consecutive characters, we would have n-1 0s.

So I wrote a little C# script to do this for me:

StringBuilder sb = new StringBuilder();
var bytes = System.IO.File.ReadAllBytes(@"C:\Users\passp\Downloads\ghost_text.txt");

var consecutive = 0;
for (int i = 3; i < bytes.Length; i++)
{
    if (bytes[i] == 0xE2)
    {
        if (consecutive>1)
        {
            sb.Append('0', consecutive - 1);
        }
        consecutive = 0;
        sb.Append('1');
        if (bytes[i] == 0xE2)
            i += 2;
    }
    else
    {
        consecutive++;
    }
}

for (int i = 1; i < sb.Length+1; i++)
{

    Console.Write(sb[i-1]);
}

Console.ReadLine();

This yields the output:

011000110110110100110001001110010010110101110010001100110011010001100100001011010110001001110100011101110110111000101101011101000110100001100101010000110010110101001000010000010101001001010011

Pasting that into an online binary to text converter, yields our flag:

cm19-r34d-btwn-theC-HARS

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