English [Internetwache CTF 2016] [Crypto 80 – Procrastination] Write Up

Description

Watching videos is fun! Hint: Stegano skills required.

Service: https://procrastination.ctf.internetwache.org

Resolution

The video attached contained 2 audio steams:
– rick roll time
– tones like on the phone

It’s called DTMF tones and corresponds to a number/character on the phone’s keypad.
Using multimon-ng (or an online site like http://dialabc.com/sound/detect/index.html – in this case the sound must be cut in 2 parts to bypass the 30s restriction) we got:

0111012701730104012206001160630123013701270610124011001370120011006001160630123

Splitted using the zero:

111 127 173 104 122 60 116 63 123 137 127 61 124 110 137 120 110 60 116 63 123

Converted from octal to ascii (TCL code):

$$ set string "111 127 173 104 122 60 116 63 123 137 127 61 124 110 137 120 110 60 116 63 123"; foreach char [split $string] { append output [subst [regsub -all {([0-9]+)} $char {[format %c [scan \1 %o]]} ] ] }; return $output
IW{DR0N3S_W1TH_PH0N3S

Flag was : IW{DR0N3S_W1TH_PH0N3S}

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