Writeup: HTB Challenge Signals

• Challenge: Signals
• Category: Hardware
• Solve date: 2025-01-26

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Description

Some amateur radio hackers captured a strange signal from space. A first analysis indicates similarities with signals transmitted by the ISS. Can you decode the signal and get the information?

Provided files

• Signal.wav

ExifTool

ExifTool Version Number         : 12.76
File Name                       : Signal.wav
Directory                       : .
File Size                       : 12 MB
File Modification Date/Time     : 2021:06:14 14:04:59+02:00
File Access Date/Time           : 2025:01:26 18:05:39+01:00
File Inode Change Date/Time     : 2025:01:26 18:02:48+01:00
File Permissions                : -rw-r--r--
File Type                       : WAV
File Type Extension             : wav
MIME Type                       : audio/x-wav
Encoding                        : Microsoft PCM
Num Channels                    : 1
Sample Rate                     : 48000
Avg Bytes Per Sec               : 96000
Bits Per Sample                 : 16
Duration                        : 0:02:08

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Slow-scan television (SSTV)

The ISS (see hint) transmits SSTV signals, i.e. static images. We need some kind of software to decode it.

QSSTV

We install QSSTV and open the file (Options -> Configurations -> Sound -> “From file”, then Start the receiver) and violà, the flag is here!