1.0 KiB
Difficulty
Easy
Category
Forensics
How To Solve
At the beginning of the audio fragment, you hear a long sequence of DTMF tones. Use an online took like dtmf-detect to decode the DTMF tones. You then get a ciphertext: 44442228333#744422255887844337446666633#. The title of the challenge contains the word 'SMS', but so far, we haven't encountered anything yet that has to do with SMS. In fact, to encode the obtained ciphertext, you have to use multitap phone decoding. This is an historic technique used to write SMS on old mobile phones with a keyboard consisting of 10 numeric keys. For example, the word "CTF" is encoded with multitap as: 222 8 333. You have to press the 2 key three times for the "C", the 8 once for the "T" and the 3 three times for the "F". Using an online decoding tool you get the following string: IGCTF PICKUPTHEPHONE. Add the curly braces and you have the flag.
Flag
IGCTF{PICKUPTHEPHONE}