Questions Debrief: Hong Kong CTF Open 2019

Below selective questions can try before the event!

Category: Crypto

Q1: Encrypted Message
Description: The following message has been encrypted with some kind of cipher, can you decrypt it?
B jif’b tewwrbo xfbz qk amcs oa kkww iywttwm tb UQMXD. Ba’a steodh ny sj G lvtnmv a afbhvik tszwivy! Zyne. Ripx’z bzm xllu: UQMXD{lbjkbatfhvux_ggiomja_srp_hbu_oeqr_jqhpwr_ec_fuvzc}

Q2: RSA 1
Description: A customer suspected that his message are cracked by somebody. Can you confirm the issue by decrypting the message below?
c:1267512865767235284579628962679981517661651162006242932307504395229069157817213250932198187
n:1441341319160614646189772775947458689224268167522603816085381857689639120119532883988453931
e:65537

Q3: Mersenne 16
File: msg, public.key (click to download )
Description: Is it possible to decrypt the message using public key?

Category: Forensics

Q1: Don’t Listen to me
File: audio.wav (click to download)
Description: I can’t get the information from the audio. Can you?

Q2: Secret Image 2
File: hkctf_open_yellow.png (click to download)
Description: Can you find the flag encoded inside the image?

Category: Reverse Engineering

Q1: Secret in Android App 2
File: Chocolate02.apk (click to download)
Description: The protection method changed. Can you find the flag this time?

Category: Misc

Q1: Solomon
File: cat.zip (click to download)
You cannot clap with only one hand, neither the video…

Q2: Alien
File: Alien.exe (Click to download)
Description: I got an exe file, but I can’t execute it… please help!
Please provide the flag in HKCTF{flag} where flag is the value of the flag.
Hint. Please check the flag value when providing the answer.