IceCTF - 60 - Blue Monday - Misc

Information#

Version#

By	Version	Comment
noraj	1.0	Creation

CTF#

• Name : IceCTF 2016
• Website : https://icec.tf/
• Type : Online
• Format : Jeopardy
• CTF Time : link

Description#

Those who came before me lived through their vocations From the past until completion, they'll turn away no more And still I find it so hard to say what I need to say But I'm quite sure that you'll tell me just how I should feel today. blue_monday

Solution#

1. Let's see what this file is!

file blue_monday
blue_monday: Standard MIDI data (format 1) using 1 track at 1/220

2. It's some MIDI file, we've to convert it into a text format. I used this online service. That gave me:

MFile 0 1 220
MTrk
0 On ch=1 n=73 v=100
220 Off ch=1 n=73 v=0
220 On ch=1 n=99 v=100
440 Off ch=1 n=99 v=0
440 On ch=1 n=101 v=100
660 Off ch=1 n=101 v=0
660 On ch=1 n=67 v=100
880 Off ch=1 n=67 v=0
880 On ch=1 n=84 v=100
1100 Off ch=1 n=84 v=0
1100 On ch=1 n=70 v=100
1320 Off ch=1 n=70 v=0
1320 On ch=1 n=123 v=100
1540 Off ch=1 n=123 v=0
1540 On ch=1 n=72 v=100
1760 Off ch=1 n=72 v=0
1760 On ch=1 n=65 v=100
1980 Off ch=1 n=65 v=0
1980 On ch=1 n=99 v=100
2200 Off ch=1 n=99 v=0
2200 On ch=1 n=107 v=100
2420 Off ch=1 n=107 v=0
2420 On ch=1 n=49 v=100
2640 Off ch=1 n=49 v=0
2640 On ch=1 n=110 v=100
2860 Off ch=1 n=110 v=0
2860 On ch=1 n=57 v=100
3080 Off ch=1 n=57 v=0
3080 On ch=1 n=95 v=100
3300 Off ch=1 n=95 v=0
3300 On ch=1 n=109 v=100
3520 Off ch=1 n=109 v=0
3520 On ch=1 n=85 v=100
3740 Off ch=1 n=85 v=0
3740 On ch=1 n=53 v=100
3960 Off ch=1 n=53 v=0
3960 On ch=1 n=73 v=100
4180 Off ch=1 n=73 v=0
4180 On ch=1 n=99 v=100
4400 Off ch=1 n=99 v=0
4400 On ch=1 n=95 v=100
4620 Off ch=1 n=95 v=0
4620 On ch=1 n=87 v=100
4840 Off ch=1 n=87 v=0
4840 On ch=1 n=49 v=100
5060 Off ch=1 n=49 v=0
5060 On ch=1 n=55 v=100
5280 Off ch=1 n=55 v=0
5280 On ch=1 n=104 v=100
5500 Off ch=1 n=104 v=0
5500 On ch=1 n=95 v=100
5720 Off ch=1 n=95 v=0
5720 On ch=1 n=109 v=100
5940 Off ch=1 n=109 v=0
5940 On ch=1 n=73 v=100
6160 Off ch=1 n=73 v=0
6160 On ch=1 n=68 v=100
6380 Off ch=1 n=68 v=0
6380 On ch=1 n=49 v=100
6600 Off ch=1 n=49 v=0
6600 On ch=1 n=53 v=100
6820 Off ch=1 n=53 v=0
6820 On ch=1 n=95 v=100
7040 Off ch=1 n=95 v=0
7040 On ch=1 n=76 v=100
7260 Off ch=1 n=76 v=0
7260 On ch=1 n=51 v=100
7480 Off ch=1 n=51 v=0
7480 On ch=1 n=116 v=100
7700 Off ch=1 n=116 v=0
7700 On ch=1 n=53 v=100
7920 Off ch=1 n=53 v=0
7920 On ch=1 n=95 v=100
8140 Off ch=1 n=95 v=0
8140 On ch=1 n=72 v=100
8360 Off ch=1 n=72 v=0
8360 On ch=1 n=52 v=100
8580 Off ch=1 n=52 v=0
8580 On ch=1 n=118 v=100
8800 Off ch=1 n=118 v=0
8800 On ch=1 n=69 v=100
9020 Off ch=1 n=69 v=0
9020 On ch=1 n=95 v=100
9240 Off ch=1 n=95 v=0
9240 On ch=1 n=97 v=100
9460 Off ch=1 n=97 v=0
9460 On ch=1 n=95 v=100
9680 Off ch=1 n=95 v=0
9680 On ch=1 n=114 v=100
9900 Off ch=1 n=114 v=0
9900 On ch=1 n=52 v=100
10120 Off ch=1 n=52 v=0
10120 On ch=1 n=118 v=100
10340 Off ch=1 n=118 v=0
10340 On ch=1 n=51 v=100
10560 Off ch=1 n=51 v=0
10560 On ch=1 n=125 v=100
10780 Off ch=1 n=125 v=0
11780 Meta TrkEnd
TrkEnd

3. Alternatively you can use midicsv that convert MIDI to CSV. It's only up to you which file you prefer to parse.

0, 0, Header, 1, 1, 220
1, 0, Start_track
1, 0, Note_on_c, 0, 73, 100
1, 220, Note_off_c, 0, 73, 0
1, 220, Note_on_c, 0, 99, 100
1, 440, Note_off_c, 0, 99, 0
1, 440, Note_on_c, 0, 101, 100
1, 660, Note_off_c, 0, 101, 0
1, 660, Note_on_c, 0, 67, 100
1, 880, Note_off_c, 0, 67, 0
1, 880, Note_on_c, 0, 84, 100
1, 1100, Note_off_c, 0, 84, 0
1, 1100, Note_on_c, 0, 70, 100
1, 1320, Note_off_c, 0, 70, 0
1, 1320, Note_on_c, 0, 123, 100
1, 1540, Note_off_c, 0, 123, 0
1, 1540, Note_on_c, 0, 72, 100
1, 1760, Note_off_c, 0, 72, 0
1, 1760, Note_on_c, 0, 65, 100
1, 1980, Note_off_c, 0, 65, 0
1, 1980, Note_on_c, 0, 99, 100
1, 2200, Note_off_c, 0, 99, 0
1, 2200, Note_on_c, 0, 107, 100
1, 2420, Note_off_c, 0, 107, 0
1, 2420, Note_on_c, 0, 49, 100
1, 2640, Note_off_c, 0, 49, 0
1, 2640, Note_on_c, 0, 110, 100
1, 2860, Note_off_c, 0, 110, 0
1, 2860, Note_on_c, 0, 57, 100
1, 3080, Note_off_c, 0, 57, 0
1, 3080, Note_on_c, 0, 95, 100
1, 3300, Note_off_c, 0, 95, 0
1, 3300, Note_on_c, 0, 109, 100
1, 3520, Note_off_c, 0, 109, 0
1, 3520, Note_on_c, 0, 85, 100
1, 3740, Note_off_c, 0, 85, 0
1, 3740, Note_on_c, 0, 53, 100
1, 3960, Note_off_c, 0, 53, 0
1, 3960, Note_on_c, 0, 73, 100
1, 4180, Note_off_c, 0, 73, 0
1, 4180, Note_on_c, 0, 99, 100
1, 4400, Note_off_c, 0, 99, 0
1, 4400, Note_on_c, 0, 95, 100
1, 4620, Note_off_c, 0, 95, 0
1, 4620, Note_on_c, 0, 87, 100
1, 4840, Note_off_c, 0, 87, 0
1, 4840, Note_on_c, 0, 49, 100
1, 5060, Note_off_c, 0, 49, 0
1, 5060, Note_on_c, 0, 55, 100
1, 5280, Note_off_c, 0, 55, 0
1, 5280, Note_on_c, 0, 104, 100
1, 5500, Note_off_c, 0, 104, 0
1, 5500, Note_on_c, 0, 95, 100
1, 5720, Note_off_c, 0, 95, 0
1, 5720, Note_on_c, 0, 109, 100
1, 5940, Note_off_c, 0, 109, 0
1, 5940, Note_on_c, 0, 73, 100
1, 6160, Note_off_c, 0, 73, 0
1, 6160, Note_on_c, 0, 68, 100
1, 6380, Note_off_c, 0, 68, 0
1, 6380, Note_on_c, 0, 49, 100
1, 6600, Note_off_c, 0, 49, 0
1, 6600, Note_on_c, 0, 53, 100
1, 6820, Note_off_c, 0, 53, 0
1, 6820, Note_on_c, 0, 95, 100
1, 7040, Note_off_c, 0, 95, 0
1, 7040, Note_on_c, 0, 76, 100
1, 7260, Note_off_c, 0, 76, 0
1, 7260, Note_on_c, 0, 51, 100
1, 7480, Note_off_c, 0, 51, 0
1, 7480, Note_on_c, 0, 116, 100
1, 7700, Note_off_c, 0, 116, 0
1, 7700, Note_on_c, 0, 53, 100
1, 7920, Note_off_c, 0, 53, 0
1, 7920, Note_on_c, 0, 95, 100
1, 8140, Note_off_c, 0, 95, 0
1, 8140, Note_on_c, 0, 72, 100
1, 8360, Note_off_c, 0, 72, 0
1, 8360, Note_on_c, 0, 52, 100
1, 8580, Note_off_c, 0, 52, 0
1, 8580, Note_on_c, 0, 118, 100
1, 8800, Note_off_c, 0, 118, 0
1, 8800, Note_on_c, 0, 69, 100
1, 9020, Note_off_c, 0, 69, 0
1, 9020, Note_on_c, 0, 95, 100
1, 9240, Note_off_c, 0, 95, 0
1, 9240, Note_on_c, 0, 97, 100
1, 9460, Note_off_c, 0, 97, 0
1, 9460, Note_on_c, 0, 95, 100
1, 9680, Note_off_c, 0, 95, 0
1, 9680, Note_on_c, 0, 114, 100
1, 9900, Note_off_c, 0, 114, 0
1, 9900, Note_on_c, 0, 52, 100
1, 10120, Note_off_c, 0, 52, 0
1, 10120, Note_on_c, 0, 118, 100
1, 10340, Note_off_c, 0, 118, 0
1, 10340, Note_on_c, 0, 51, 100
1, 10560, Note_off_c, 0, 51, 0
1, 10560, Note_on_c, 0, 125, 100
1, 10780, Note_off_c, 0, 125, 0
1, 11780, End_track
0, 0, End_of_file

4. I used the first one because I found it's was easier to parse.
5. To get the flag, we need to the value of n into ASCII only for On/Note_on_c lines (or only Off/Note_off_c,) because each value is in double.
6. Here's my script:

import re

filename = "blue_monday_alt.txt"

binary = ""
text = ""

with open(filename, 'r') as fh:
    for line in fh:
        #print(line.rstrip('\n'))
        if 'On' in line:
            regex_result = re.compile(r'n=(.*?)\sv=').search(line)
            if regex_result:
                text += chr(int(regex_result.group(1)))

print(text)

7. And the result:

python3 blue_monday.py
IceCTF{HAck1n9_mU5Ic_W17h_mID15_L3t5_H4vE_a_r4v3}