NPST 01. Mobildetektiven: SMS cipher

Task description

Her får du den første oppgaven!

Under etterforskningen av hendelsen på jule-verkstedet har vi oppdaget noe rart. Et av meldingssystemene som sender varslinger til beredskapsvaktene for verkstedet har sendt en SMS til et ukjent nummer. Meldingen er dessverre helt uleselig for oss, så vi trenger dine mobildetektiv-egenskaper. Når du finner ut av det, send meg svar på formatet PST{ditt svar her}.

7-4 9-3 7-4 8-1 3-2 6-1 0-1
4-3 6-2 3-3 4-3 7-4 3-2 7-3
8-1 0-1 4-1 7-3 8-2 6-2 5-2
3-2 7-3 0-1 4-3 6-2 2-3 6-3
6-1 4-3 6-2 4-1

- Tastefinger

Solution

Okay, this is related to something with a phone, an SMS or an unknown mobile number. It also looks like a task where you just need to find the right tool to decode the cipher (this is typical for NPST).

We don’t have much more to go on, so tools like cyberchef, dcode.fr and boxentriq will come in handy. These tools specifically:

Dcode’s cipher identifier correctly identifies the cipher as “Multi-tap Phone (SMS)”. If we decode the numbers in the task description with this tool we get this:

SYSTEM-INFISERT-GRUNKER-INCOMING

And, after failing to deliver PST{SYSTEM-INFISERT-GRUNKER-INCOMING} as a flag, I figured out that the dashes had to be replaced with spaces for the flag to be accepted.

TL;DR

  1. https://www.dcode.fr/cipher-identifier
  2. https://www.dcode.fr/multitap-abc-cipher
  3. Replace - with 

Alternatively:

  1. Go to https://dcode.fr/en
  2. Search for “phone”, “sms”, “mobile”
  3. Find a cipher that gives readable output
  4. Replace - with 

Flag: PST{SYSTEM INFISERT GRUNKER INCOMING}