feat: add sound-of-sms-secrets challenge

sound-of-sms-secrets/README.md

@@ -0,0 +1,7 @@
+# sound of secrets
+## Text
+A clandestine audio file, a digital whisper, has been intercepted. Within its depths, a hidden message awaits discovery. A series of cryptic tones, a puzzle waiting to be solved. Decipher this auditory riddle, and you will unlock the secret, a digital treasure hidden in sound.
+## Files
+[audio.wav](audio.wav)
+## How to Deploy
+N/A

sound-of-sms-secrets/SOLUTION.md

@@ -0,0 +1,9 @@
+## 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](https://unframework.github.io/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](https://www.dcode.fr/multitap-abc-cipher) you get the following string: `IGCTF PICKUPTHEPHONE`. Add the curly braces and you have the flag.
+
+## Flag
+IGCTF{PICKUPTHEPHONE}