Beep64

Challenge Description

Every CTF needs a base64 challenge... right?

Attachments

• chall.zip

Solution

• Unzip the file, we get a wav file which is 37 mins long

• Listening to the audio file, it is DTMF tones

• Online decoders dont work for such a long audio file

• Using this repo we can decode the audio file

• DTMF Output: out.txt

• Removing the * and replacing with spaces

• Decoding the rest using T9 Decoder

• Replace

  • SPACE: nothing

  • ZERO: 0

  • ONE: 1

• Decode using Binary and then Base64 decoding gives us the flag

Cyberchef Recipe

FLAG

flag{0421a964add97ff041431e2418e64508}

Resources

• DTMF Decoder: https://github.com/ribt/dtmf-decoder

• T9 Decoder: https://www.cachesleuth.com/vanity.html

• Cyberchef: https://gchq.github.io/CyberChef/