Mayday

This is a writeup of the crypto challenge Mayday! from the TFC CTF

Points: 50

Premise

We are sinking! The nearest ship got our SOS call, but they replied in pure gobbledygook! Are ye savvy enough to decode the message, or will we be sleepin’ with the fish tonight? All hands on deck!

Whiskey Hotel Four Tango Dash Alpha Romeo Three Dash Yankee Oscar Uniform Dash Sierra One November Kilo India November Golf Dash Four Bravo Zero Uniform Seven

Flag format: TFCCTF{RESUL7-H3R3}

Challenge chiphertext:

Whiskey Hotel Four Tango Dash Alpha Romeo Three Dash Yankee Oscar Uniform Dash Sierra One November Kilo India November Golf Dash Four Bravo Zero Uniform Seven

Observations

This looks a lot like the ICAO/NATO alphabet , so we can make an attemt to decode it in that format.

• Note, a less guess-y way to identify the ciphertext, could be to use the cipher identifier from dcode.fr, which also identifies the ciphertext as our previous assumption.

Solution

We can either decode this by hand or using the decoder from dcode.fr.

Either way, decoding the ciphertext gives us:

WH4T-AR3-YOU-S1NKING-4B0U7

Which when formatted gives us our flag: TFCCTF{WH4T-AR3-YOU-S1NKING-4B0U7}

Tools and sources used:

• The ICAO/NATO phonetic alphabet
• Optional: dcode.fr