Challenge Name: Serial Killer 1
Category: Osint
CTF: MOJO-JOJO
Description: Your only starting evidence: a photo recovered from a victim’s phone in Kairouan.
Flag Format :MOJO-JOJO{City_NN} NN: First and Second of digits the phone Number
Solution#
Initial Analysis#
The handout was a pixelated PNG image, suggesting that the information inside was intentionally obscured or encrypted in some way. The pixelation indicated that steganography or image encryption was likely used to hide the flag.
Step 1: Identifying the Decryption Method#
Since the image appeared to be encrypted rather than just visually obscured, I decided to use an image decryption tool. I navigated to Image Online Encrypt/Decrypt to attempt decrypting the image.
Step 2: Finding the Decryption Key#
The decryption tool required a key. Returning to the challenge description, I noticed that only one word was highlighted in bold: Kairouan. This was clearly the hint for the decryption key.
Key used: Kairouan
Step 3: Decrypting the Image#
After entering “Kairouan” as the key in the Image Online Encrypt/Decrypt tool, the hidden image was successfully revealed.
Step 4: Analyzing the Revealed Information#
The decrypted image showed:
- A number displayed prominently: 71
- An image of a cafe located in Tunis
The challenge required finding both the city and a two-digit magic number. Based on the decrypted image:
- City: Tunis
- Magic Number: 71
Flag#
Combining the location and the two-digit number according to the specified format:
MOJO-JOJO{Tunis_71}
