Tags: forensics 


# whyOS
***Category: Forensics***
> *Have fun digging through that one. No device needed.*
> *Note: the flag is not in flag{} format*
> *HINT: the flag is literally a hex string. Put the hex string in the flag submission box*
> *Update (09/15 11:45 AM EST) - Point of the challenge has been raised to 300 Update*
> *Sun 9:09 AM: its a hex string guys*
## Solution
For this challenge, we are given two files: [com.yourcompany.whyos_4.2.0-28debug_iphoneos-arm.deb](com.yourcompany.whyos_4.2.0-28debug_iphoneos-arm.deb) and [console.log](console.log). Admittedly, I had almost no experience with iOS prior to this, so my solution relied heavily on the hints given and a bit of luck. I probably would not have found the flag otherwise.

We begin by taking a quick glance through the `console.log` to see what we were dealing with. The `console.log` turned out to be an extremely large file containing 185,088 log entries, which meant `com.yourcompany.whyos_4.2.0-28debug_iphoneos-arm.deb` had to contain some clues to help us narrow down the search criteria. I begin looking through the file for any clues that might point us towards where the flag might be. After a quick search through the contents of the files, we find a file named `Root.plist` located in `data.tar.lzma/Library/PreferenceBundles/whyOSsettings.bundle/` which contained the following snippet of code:

<string>Put the flag{} content here</string>

Since I had almost no experience with iOS prior to this, I was not sure what exactly it meant, but it was one of the only files which showed any indication of where the flag could possibly be. I assumed this was the format for the log entry where the flag was hiding, so I figured it wouldn't hurt to try a quick search. Based on the snippet of code above, I assumed the flag was in the last field of the log entry. Combining this with the hint, `the flag is literally a hex string`, I was able to narrow down my search results immensely. I also assumed the flag was at least 32 characters long in order to narrow down the initial search results even more. Using this criteria, I wrote a quick python script to filter through the log entries:
import re
with open('console.log', 'r') as f:
data = [i for i in f]

matches = []
for i in data:
if i.isspace():
if re.match('^[a-f0-9]{32,}$', i.split()[-1], re.I):

for i in matches:
print i
Surprisingly, the script returned only three results:
default 19:09:48.701395 -0400 securityd session[0x102c43610] failed to decrypt, session: <Done c i FPDk 6:7 PT 0 Mrse>, mk: <SecOTRFullDHKeyRef@0x102b4ba00: x: E4FF45A23909E20AB8FEA0A8C9563737A326EDA49CC91C55538316A30569D27F y: 53627A4C1446D7BE3956C5E0CB55E31AD23CF7490D9B4380CF4057423A73DF38 [5EC13ED1FFE1BDCF875BA2CD31C0A017524672C7]>, mpk: <SecOTRFullDHKeyRef@0x102b55560: x: F7009D0863F90B650E0D8725CC04E7D375572EF97EACBB5AC4E14806713C8AAE y: 744B2996A4CFC79D95D5E5B87D2A8ADC205C4A0383DCA04344B87B4FCABB7A87 [6CE646617B058CDFB1DCBBF5C3DE3C991219C0FE]>, tpk: <SecOTRPublicDHKeyRef@0x102b2c640: x: E705E1726FE049DBD6AF9713BF98FB0EEA97F2DA63B63B15AE83C8789D4E0B2D y: 7A53E0F1EB2DEADEA2012AFBFFCA8B7524EEA84E65C0C771A24536EE5DD456D9 [621BF69F134448C3FAE3BCB114CF58C446DD2D67]>, tk: <SecOTRPublicDHKeyRef@0x102b4b670: x: A183EF7B34E0924D1A49317AB2DDC77365BFCAF158A058A8BD3D9896D1FF3E8A y: 4774FF271BA4CFCE6B5A787AC9B74AEC70574A7B62B8D5189D76169835F0195A [82EE8C5862AF5E2017A1F9D92DD86F3AEF796B30]>, chose tktu: <SecOTRPublicDHKeyRef@0x102b2c640: x: E705E1726FE049DBD6AF9713BF98FB0EEA97F2DA63B63B15AE8
default 19:09:48.704576 -0400 securityd session[0x102c402d0] failed to decrypt, session: <Done c i FPdk 319:319 PT 0 Mrse>, mk: <SecOTRFullDHKeyRef@0x102b1e210: x: 06B7C203FA950F848F46E3C9AD4946141EACE5E8015F58BE1E11C2D343EBF1E0 y: 19E64A4A8C1A420E1702C38972A5754C3564F24C5F823175CFA6A4B9A074210E [27AB14752A96A358E385E7161968EE4DF90A34E5]>, mpk: <SecOTRFullDHKeyRef@0x102b4b430: x: 15D5FF367C910C32A903391C61DD3BCCD59DD86F1C4F9ABB39E4C789BC2802F2 y: 7D1D9CC90611ABEB8BADB606816D55DF1BC09358EEFAAD65537CD7569DDC4CE9 [43FDF4F8ED5094C1CB3F63A6E81FBC869F1B07FE]>, tpk: <SecOTRPublicDHKeyRef@0x10294f220: x: 9EB6562D61A0BB1C1FFCEF1C1C184AB2BC39E6889126370AEE47BD6EE4BC0D01 y: 460C25FEDAD5A42470AD029B757F3849D2A6271CDB0176D7A1DB74929628FF05 [C5C06D0001663B7552BBA8ED442A7E13DEA90D42]>, tk: <SecOTRPublicDHKeyRef@0x102c80750: x: 07282DF3961CDDEB26007E061740FF4F2727B73F36A40006C747B9805635C866 y: 067FCCEB2ACB818E748B4525CBF3816D33B3949806028D97D9C77EC4D48EFD80 [7649E1A68A560B72F76F8C27176A2B6B7970C335]>, chose tktu:

Original writeup (https://github.com/scai16/CTF/tree/master/2018/CSAW%20CTF%202018/whyOS).