Flagvent 2025: Day 7
FV25.07 - Captured Noise
Difficulty
medium
Categories
fun
Description
Rudolph wanted to make a call, but when he took off the phone headset, he heard some strange sounds.
Author
lukyluke_chSolution
The only file in today’s challenge is a captured.wav file. The audio is 1:01 long and contains modem-like tones. The first 17 seconds have a slightly different tone. This is typical of a dial-up modem conversation where a handshake occurs before data is transmitted.
Our immediate approach is to use minimodem, a software modem, to demodulate the audio and recover the digital data that was originally encoded. We run it with a common baud rate of 1200.
$ minimodem --rx 1200 -f captured.wavThe command succeeds and produces the following data:
### CARRIER 1200 @ 1200.0 Hz ###
█████ █████ ███████ █████ █████ █████ █████
░░███ ░░███ ███░░░░░███ ░░███ ░░███ ░░███ ░░███
░███ ░███ ███ ░░███ ░███ ░███ ░░███ ███
░███████████ ░███ ░███ ░███ ░███ ░░█████
░███░░░░░███ ░███ ░███ ░███ ░███ ░░███
░███ ░███ ░░███ ███ ░███ █ ░███ █ ░███
█████ █████ ░░░███████░ ███████████ ███████████ █████
░░░░░ ░░░░░ ░░░░░░░ ░░░░░░░░░░░ ░░░░░░░░░░░ ░░░░░
████████ █████ █████ █████
███░░░░███ ███░░░███ ███░░░███ ███░░░███
░███ ░███ ███ ░░███ ███ ░░███ ███ ░░███
░░█████████░███ ░███░███ ░███░███ ░███
░░░░░░░███░███ ░███░███ ░███░███ ░███
███ ░███░░███ ███ ░░███ ███ ░░███ ███
░░████████ ░░░█████░ ░░░█████░ ░░░█████░
░░░░░░░░ ░░░░░░ ░░░░░░ ░░░░░░
The Holly 9000 is an interactive AI which captures wishes from all over the world and produces presents on demand.
Please verify yourself:
User> Santa
Thanks you Santa, please resolve the challenge: http://ranta.ch/fv25/holly-9000/
Verification> It is me, Santa
Well done, the verification was successfull.
Command> ?
Play
Start
List
Exit
Command> Play
Listen to some nice tunes: http://ranta.ch/fv25/holly-9000/player.html
Command> List
# Name Naughty/Nice Wish
1 Aaron Mills Nice A mechanical keyboard
2 Abigail Hart Naughty A "behave" handbook
3 Adrian Cole Nice Noise-cancelling headphones
4 Aisha Khan Nice A cozy wool blanket
5 Alan Reeves Naughty An apology journal
6 Alex Park Nice A camera drone
7 Alice Monroe Nice A watercolor set
8 Alicia Torres Naughty A time-management planner
9 Allan Briggs Nice A set of chef knives
10 Amanda Lee Nice A bonsai starter kit
11 Amber Flynn Naughty A cookbook for polite guests
12 Amelia Stone Nice A telescope
13 Andre Novak Nice A vintage record player
14 Andrew White Naughty A book on empathy
15 Angela Ross Nice A spa gift box
16 Anita Desai Nice A language learning app subscription
17 Anna Wu Naughty A gardening manual (for neighbors)
18 Anthony Cruz Nice A portable espresso maker
19 April Benson Naughty A "how to listen" course
20 Ariel Gordon Nice A leather journal
21 Arnold Price Naughty A kid’s manners book
22 Ashley Kim Nice A silk scarf
23 Ashton Velez Nice A set of board games
24 Audrey Park Naughty A noise-reduction device
25 Austin Hayes Nice A fitness tracker
26 Ava Bennett Nice A handcrafted necklace
27 Barbara Klein Naughty A declutter starter kit
28 Ben Carter Nice A portable projector
29 Bethany Cole Nice An indoor herb garden kit
30 Bianca Ramos Naughty A budget planner
31 Blake Turner Nice A pair of hiking boots
32 Brandon Scott Naughty A conflict-resolution book
33 Brenda Ortiz Nice A pottery class voucher
34 Brian Fox Nice A smart home speaker
35 Brianna Lake Naughty A punctuality alarm clock
36 Brock Mason Nice A barbecue tool set
37 Brooke Daniels Nice A handwoven throw
38 Caleb Rhodes Naughty A "roommate etiquette" guide
39 Camila Silva Nice A digital art tablet
40 Candice Owens Naughty A listening skills workbook
41 Carl Meyer Nice A whiskey tasting kit
42 Carly Nguyen Nice A subscription box (books)
43 Carmen Lopez Naughty A volunteer shift (charity)
44 Carter Lane Nice A smartwatch
45 Cassandra Pike Nice A concert ticket voucher
46 Charles Beck Naughty A cooking class (to share)
47 Charlotte Gale Nice A yoga mat + classes
48 Chloe Winters Nice A film photography starter kit
49 Chris O'Neil Naughty A "stop interrupting" badge
Press Enter to Continue...
Command>
50 Christian Ford Nice A weekend getaway voucher
51 Christine Shaw Naughty A recipe for patience
52 Claire Bennett Nice A specialty tea collection
53 Claudia Ruiz Nice A sewing machine
54 Cody Wallace Naughty A manners refresher course
55 Colin Hartman Nice A woodworking starter set
56 Courtney Price Nice A gourmet chocolate box
57 Craig Nolan Naughty A library fine to pay (metaphorically)
58 Crystal Vega Nice A fitness class pass
59 Curtis Lane Naughty A volunteer apology letter kit
60 Cynthia Morales Nice A personalized cookbook
61 Daisy Ford Nice A set of scented candles
62 Damian Cross Naughty A mediation app subscription
63 Dana Blake Nice A pottery wheel session
64 Daniel Ortiz Nice A vintage watch
65 Daniela Russo Naughty A "think before you speak" poster
66 Darren Cole Nice A gourmet spice rack
67 David Kim Nice A high-end backpack
68 Dawn Ellis Naughty A neighborhood goodwill task
69 Dean Harper Nice A drone photography lesson
70 Deborah Lane Nice A floral arranging kit
71 Derek Shaw Naughty A punctuality training calendar
72 Diana Flores Nice A subscription to a science magazine
73 Dominic Price Naughty A manners tea party invite
74 Donna Hale Nice A luxury robe
75 Dylan Nguyen Nice A coding course
76 Edith Palmer Naughty A kindness challenge pack
77 Edward Miles Nice A gourmet coffee subscription
78 Eleanor West Nice A handcrafted pottery set
79 Elijah Grant Naughty A neighborhood repair volunteer day
80 Elizabeth Young Nice A set of classic novels
81 Ella Morrison Nice A bakeware set
82 Emily Dawson Naughty A noise-awareness program
83 Emma Brooks Nice A botanical print set
84 Eric Wallace Nice A barbecue smoker
85 Erin Gilbert Naughty A civil-conversation class
86 Ethan Russell Nice A mountain bike
87 Eva Sinclair Naughty A book on thoughtful communication
88 Evan Price Nice A VR headset
89 Faith Jordan Nice A handmade quilt
90 Felix Navarro Naughty A community service voucher
91 Fiona Chen Nice A silk pillowcase set
92 Gabriella Diaz Nice A film festival pass
93 Gary Banks Naughty A time capsule of apologies
94 Gemma Reeves Nice A designer handbag
95 George Holt Naughty A "show up on time" watch
96 Grace Kim Nice A watercolor class subscription
97 Greg Owens Naughty A cooperation board game
98 Hannah Bishop Nice A musical instrument (ukulele)
99 Harry Stone Naughty A patience-building puzzle set
100 Hazel Murray Nice A solar-powered charger
Press Enter to Continue...
Command>
101 Hector Morales Naughty A community garden shift
102 Holly Price Nice A weekend yoga retreat
103 Howard Finch Naughty A neighborhood cleanup kit
104 Hugo Alvarez Nice A gourmet cheese-making kit
That's all...
Command> Exit
See you Soon Santa.
Exit...
### NOCARRIER ndata=7399 confidence=4.857 ampl=1.001 bps=1200.00 (rate perfect) ###We spend some time looking for a flag in the output but have no luck. Next, we head to the website http://ranta.ch/fv25/holly-9000/ to continue our search for the glorious flag!
Inspecting the website’s source code and searching for the word flag leads us to this section of code:
@flag-face{format("flag"); unicode-range: U+46, U+56, U+32, U+35, U+7b,
U+57, U+68, U+40, U+74, U+2d, U+41, U+2d, U+77, U+31, U+72, U+33, U+64,
U+2d, U+4e, U+6f, U+31, U+73, U+65, U+7d}Seeing the values 46 56 32 35 in hex suggests they may form the flag. Converting them to ASCII gives us our daily flag!
Flag:
FV25{Wh@t-A-w1r3d-No1se}