Flagvent 2025: Day 1

FV25.01 - welcome

Difficulty
easy

Categories
fun

Description
Welcome to Flagvent
Hint: This is not a stego challenge, all the puzzle pieces required for the challenge are clearly visible.

Author
Last Place

Solution

Inside our tar file, we find the following welcome.jpg Christmas tree:

Immediately, we notice this glorious tree is decorated with parts of a QR code! It looks like there might be enough pieces to reconstruct the original code. We decide to use Photoshop to crop out the QR code fragments with the magnetic lasso tool. It’s a slow and painful process, but once we’re done, we have all the individual pieces:

At this point, for no particular reason, we decide to piece together only the red fragments to form a QR code, ignoring the blue, black, and green ones. By counting the pixels in the finder patterns (7×7), we deduce that it’s a 29×29 QR code. Using our image editor, we distort and align the pieces until it looks fairly reasonable. There’s a gap in the middle, but it doesn’t end up mattering.

We try scanning the QR code, but it’s not quite clean enough to be read. However, there’s enough data for the original message to be recoverable thanks to the error correction feature of QR codes. So, we reconstruct it manually by writing out rows of 0s and 1s to represent the white and black pixels.

11111110110110110101001111111
10000010001110111111001000001
10111010011101110000001011101
10111010100011100011001011101
10111010011010000111001011101
10000010000110101111101000001
11111110101010101010101111111
00000000001000000110100000000
00101110100000000011010001001
00100001000000001100111001000
11111111100000000000111110011
10101001000000000010101101011
10010010000000000011111110011
01011001000000000010111000001
10001110000000000000011100001
00101001100000000000001111000
00011110101000000000111001010
00101100100010100000100000110
10000111111111010010011011111
01001100110010100001100010010
10111010101010100100111110100
00000000111100000001100011011
11111110000001000001101010001
10000010110111010010100011000
10111010101111101010111111011
10111010011010000101000010000
10111010101110011101000110001
10000010001010110101100000010
11111110010110000001100110011

Using Dave Eddy’s online Binary Hex to QR Code tool, we generate the QR code image shown below:

Scanning this QR code gives us our daily flag.

Flag:

FV25{Welcome-2-FlagVent}