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Encrypt10n

Table of Contents

  1. Encrypt10n (Part 1)
  2. Encrypt10n (Part 2)
  3. Conclusion

Encrypt10n (Part 1)

Overview

Background

We made a memory dump on the criminal machine after entering the crime scene. Our investigator thought he was using encryption software to hide the secret. can you help me to detect it?

Q1 : crew{password}

Link

Author : 0xSh3rl0ck

Find the flag

In this challenge, we can download a file:

┌[siunam♥Mercury]-(~/ctf/CrewCTF-2023/Forensics/Encrypt10n)-[2023.07.08|21:10:29(HKT)]
└> ls -lah dump.raw && file dump.raw 
-rw-r--r-- 1 siunam nam 1.0G Jul  8 20:49 dump.raw
dump.raw: Windows Event Trace Log

As you can see, it’s a memory dump file.

To perform memory forensic, we can use a tool called Volatility. Through out this challenge, I’ll use Volatility version 2 (volatility2).

First, we need to know the machine’s profile:

┌[siunam♥Mercury]-(~/ctf/CrewCTF-2023/Forensics/Encrypt10n)-[2023.07.08|21:12:15(HKT)]
└> python2 /opt/volatility/vol.py imageinfo -f dump.raw 
[...]
          Suggested Profile(s) : Win7SP1x86_23418, Win7SP0x86, Win7SP1x86_24000, Win7SP1x86
[...]

Then, we can find all the processes in the memory dump:

┌[siunam♥Mercury]-(~/ctf/CrewCTF-2023/Forensics/Encrypt10n)-[2023.07.08|21:13:38(HKT)]
└> python2 /opt/volatility/vol.py --profile=Win7SP1x86_23418 -f dump.raw pslist
[...]
0x85c596c0 TrueCrypt.exe          3196   1384      2       67      1      0 2023-02-16 12:02:07 UTC+0000                                 
[...]

In here, we can found that there’s a TrueCrypt.exe process.

TrueCrypt is a discontinued source-available freeware utility used for on-the-fly encryption (OTFE). It can create a virtual encrypted disk within a file, or encrypt a partition or the whole storage device (pre-boot authentication). (From https://en.wikipedia.org/wiki/TrueCrypt)

In volatility2, there’s a plugin called truecryptsummary, which displays TrueCrypt summary information:

┌[siunam♥Mercury]-(~/ctf/CrewCTF-2023/Forensics/Encrypt10n)-[2023.07.08|21:15:29(HKT)]
└> python2 /opt/volatility/vol.py --profile=Win7SP1x86_23418 -f dump.raw truecryptsummary
[...]
Registry Version     TrueCrypt Version 7.0a
Password             Strooooong_Passwword at offset 0x8d23de44
Process              TrueCrypt.exe at 0x85c596c0 pid 3196
Service              truecrypt state SERVICE_RUNNING
Kernel Module        truecrypt.sys at 0x8d20a000 - 0x8d241000
Symbolic Link        Volume{a2e4e949-a9a8-11ed-859c-50eb71124999} -> \Device\TrueCryptVolumeZ mounted 2023-02-16 12:02:56 UTC+0000
Driver               \Driver\truecrypt at 0x3f02fc98 range 0x8d20a000 - 0x8d240980
Device               TrueCrypt at 0x84e2a9d8 type FILE_DEVICE_UNKNOWN

Nice! We found the password!

Encrypt10n (Part 2)

Overview

Background

Congrats Investigator for finding the first part can you use it to get the secret message?

Link

Author : 0xSh3rl0ck

Find the flag

In this challenge, we can download a file:

┌[siunam♥Mercury]-(~/ctf/CrewCTF-2023/Forensics/Encrypt10n)-[2023.07.08|21:21:39(HKT)]
└> ls -lah flag && file flag
-rw-r--r-- 1 siunam nam 10M Jul  8 21:18 flag
flag: data
┌[siunam♥Mercury]-(~/ctf/CrewCTF-2023/Forensics/Encrypt10n)-[2023.07.08|21:21:52(HKT)]
└> head -n 3 flag
K��3-��J,K�}��W��)29[|d ���C�6k��A�~�)���DA29Kw����`�u���6�B�?}����0e�]UbƢLj���!�!w.�W|z�'���;������1��F�-��q�y����ԝD&�o�e�{J#�%�|���\D�����&��%+}����ʖ�V��vl˾�����4���_ ���P:���o�P���=Βr��s�XD��av闐�L��j� �1og���@��ye�e{�
��p4�~,�dшkٙ�s�5��܏��:�y��rН�����l|�2�=J�?�[�Θ��n���vZލ�����Q����"�����{��<v]w+��>�Ǜ�JA�6��o���3��_����./6����F�ܽ
����/��е�`�����ɍ�Z$����>K�P~ꦓh������N�:�6�/��;{$^���SԮ�ɒ|��S�����^z�'DJQ7�N�Xl��M�3ơ\���لj�>���q�

As you can see, the flag file is just some raw bytes.

Based on the previous part, the flag file should be encrypted with TrueCrypt.

So, we can use truecrypt2john to crack it:

┌[siunam♥Mercury]-(~/ctf/CrewCTF-2023/Forensics/Encrypt10n)-[2023.07.08|21:20:00(HKT)]
└> truecrypt2john flag > flag.truecrypt
┌[siunam♥Mercury]-(~/ctf/CrewCTF-2023/Forensics/Encrypt10n)-[2023.07.08|21:20:07(HKT)]
└> john --wordlist=/usr/share/wordlists/rockyou.txt orestis_id_rsa_hash.txt
┌[siunam♥Mercury]-(~/ctf/CrewCTF-2023/Forensics/Encrypt10n)-[2023.07.08|21:20:10(HKT)]
└> nano password.txt
┌[siunam♥Mercury]-(~/ctf/CrewCTF-2023/Forensics/Encrypt10n)-[2023.07.08|21:20:23(HKT)]
└> john --wordlist=password.txt flag.truecrypt 
[...]
Strooooong_Passwword (flag)

Can confirm the password is Strooooong_Passwword.

To decrypt the file file, we can use cryptsetup. (All steps are from https://kenfavors.com/code/how-to-open-a-truecrypt-container-using-cryptsetup/)

┌[siunam♥Mercury]-(~/ctf/CrewCTF-2023/Forensics/Encrypt10n)-[2023.07.08|21:31:31(HKT)]
└> sudo cryptsetup --type tcrypt open flag flag 
Enter passphrase for flag:

Note: The first flag is the encrypted flag file, the second one is a name of your choice.

┌[siunam♥Mercury]-(~/ctf/CrewCTF-2023/Forensics/Encrypt10n)-[2023.07.08|21:37:26(HKT)]
└> mkdir /mnt/flag

┌[siunam♥Mercury]-(~/ctf/CrewCTF-2023/Forensics/Encrypt10n)-[2023.07.08|21:32:33(HKT)]
└> sudo mount -o uid=1000 /dev/mapper/flag /mnt/flag 

┌[siunam♥Mercury]-(~/ctf/CrewCTF-2023/Forensics/Encrypt10n/file)-[2023.07.08|21:32:40(HKT)]
└> ls -lah /mnt/flag  
total 12K
drwxrwxrwx 1 siunam root 4.0K Feb 16 19:38 .
drwxr-xr-x 3 root   root 4.0K Jul  8 21:30 ..
-rwxrwxrwx 2 siunam root 2.4K Feb 12 01:08 flaaaaaaaaaaaaaaaaaaaaaaaag.txt
┌[siunam♥Mercury]-(~/ctf/CrewCTF-2023/Forensics/Encrypt10n/file)-[2023.07.08|21:32:44(HKT)]
└> cat /mnt/flag/flaaaaaaaaaaaaaaaaaaaaaaaag.txt 
Vm0wd2QyUXlVWGxWV0d4V1YwZDRXRmxVU205V01WbDNXa2M1VjFac2JETlhhMk0xVjBaS2MySkVUbGhoTWsweFZtcEJlRll5U2tWVWJHaG9UV3N3ZUZadGNFdFRNVWw1VTJ0V1ZXSkhhRzlVVmxaM1ZsWmFkR05GWkZwV01VcEpWbTEwYTFkSFNrZGpSVGxhVmpOU1IxcFZXbUZrUjA1R1UyMTRVMkpIZHpGV1ZFb3dWakZhV0ZOcmJGSmlSMmhZV1d4b2IwMHhXbGRYYlhSWFRWZDBObGxWV2xOVWJGcFlaSHBDVjAxdVVuWlZha1pYWkVaT2MxZHNhR2xTTW1oWlYxWmtNRmxXVWtkV1dHaFlZbGhTV0ZSV2FFTlNiRnBZWlVoa1YwMUVSbGRaTUZaM1ZqSktWVkpZWkZkaGExcFlXa1ZhVDJNeFpITmhSMnhUVFcxb1dsWXhaRFJWTVZsNFUydGthbEp0VWxsWmJGWmhZMVpzY2xkdFJteFdia0pIVmpKNFQxWlhTa2RqUm14aFUwaENSRlpxU2tabFZsSlpZVVprVTFKWVFrbFhXSEJIVkRKU1YxZHVUbFJpVjJoeldXeG9iMWRXV1hoYVJGSnBUV3RzTkZkclZtdFdiVXB5WTBac1dtSkhhRlJXTVZwWFkxWktjbVJHVWxkaWEwcElWbXBLZWs1V1dsaFRhMXBxVWxkb1dGUlhOVU5oUmxweFVtMUdUMkpGV2xwWlZWcGhZVWRGZUdOSE9WaGhNVnBvVmtSS1QyTXlUa1phUjJoVFRXMW9lbGRYZUc5aU1XUnpWMWhvWVZKR1NuQlVWM1J6VFRGU1ZtRkhPVmhTTUhCNVZHeGFjMWR0U2toaFJsSlhUVVp3VkZacVJuZFNWa1p5VDFkc1UwMHlhRmxXYlhCTFRrWlJlRmRzYUZSaVJuQnhWV3hrVTFsV1VsWlhiVVpPVFZad2VGVXlkREJXTVZweVkwWndXR0V4Y0hKWlZXUkdaVWRPU0U5V1pHaGhNSEJ2Vm10U1MxUnRWa2RqUld4VllsZG9WRlJYTlc5V1ZtUlhWV3M1VWsxWFVucFdNV2h2V1ZaS1IxTnNaRlZXYkZwNlZGUkdVMk15UmtaUFYyaHBVbGhDTmxkVVFtRmpNV1IwVTJ0a1dHSlhhRmhaVkVaM1ZrWmFjVkp0ZEd0U2EzQXdXbFZhYTJGV1NuTmhNMmhYWVRGd2FGWlVSbFpsUm1SMVUyczFXRkpZUW5oV1Z6QjRZakZaZUZWc2FFOVdlbXh6V1d0YWQyVkdWWGxrUkVKWFRWWndlVll5ZUhkWGJGcFhZMGhLVjJGcldreFdha3BQVWpKS1IxcEdaRTVOUlhCS1ZqRmFVMU14VlhoWFdHaFlZbXhhVjFsc2FHOVdSbXhaWTBaa1dGWnNjRmxaTUZVMVlWVXhXRlZ1Y0ZkTlYyaDJWMVphUzFJeFRuTmFSbFpYWWtadmVsWkdWbUZaVjFKR1RsWmFVRll5YUhCVmJHaENaREZrVjFadE9WVk5WbkF3VlcwMVMxWkhTbGhoUm1oYVZrVmFNMVpyV21GalZrcDFXa1pPVGxacmIzZFhiRlpyWXpGVmVWTnVTbFJoTTFKWVZGYzFiMWRHYkZWU2EzQnNVbTFTZWxsVldsTmhSVEZaVVc1b1YxWXphSEpXVkVaclVqRldjMkZGT1ZkaGVsWjVWMWQwWVdReVZrZFdibEpyVWtWS2IxbFljRWRsVmxKelZtNU9XR0pHY0ZoWk1GSlBWMnhhV0ZWclpHRldNMmhJV1RJeFIxSXlSa2hoUlRWWFYwVktSbFpxU2pSV01XeFhWVmhvWVZKWFVsWlpiWFIzWWpGV2NWTnRPVmRTYlhoNVZtMDFhMVl4V25OalNHaFdWak5vY2xaclZYaFhSbFp6WVVaa1RtRnNXazFXYWtKclV6Rk9SMVp1VWxCV2JGcFlXV3RvUTJJeFdrZFdiVVphVm14c05WVnRkRzlWUmxsNVlVWm9XbGRJUWxoVk1GcGhZMVpPY1ZWc1drNVdNVWwzVmxSS05GWXhWWGxUYTJSVVlsVmFWbFp0ZUhkTk1WcHlWMjFHYWxacmNEQlZiVEV3VmpKS2NsTnJiRmROYmxKeVdYcEdWbVF3TVVsaVIwWnNZVEZ3V1ZkWGVHOVJNVkpIVld4YVlWSldjSE5WYlRGVFYyeHNjbGRzVG1oU1ZFWjZWVEkxYjFZeFdYcGhSMmhoVWtWYVlWcFZXbXRrVmxaMFpVWk9XRkpyY0ZwV2ExcGhXVlpzVjFSclpGZGlhelZYV1cxek1WWXhXblJsUjBaWFlrWktWMVpYTlV0VlZsWlZUVVJyUFE9PQ==

Uhh… The flaaaaaaaaaaaaaaaaaaaaaaaag.txt file is in base64 encoding. (You can tell it’s base64 encoded is because the last 2 characters are =, which is a padding character in base64 encoding)

Let’s base64 decode it:

┌[siunam♥Mercury]-(~/ctf/CrewCTF-2023/Forensics/Encrypt10n)-[2023.07.08|21:39:58(HKT)]
└> nano flag.b64 
┌[siunam♥Mercury]-(~/ctf/CrewCTF-2023/Forensics/Encrypt10n)-[2023.07.08|21:40:08(HKT)]
└> base64 -d flag.b64 
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

Bruh, base64 heaven…

┌[siunam♥Mercury]-(~/ctf/CrewCTF-2023/Forensics/Encrypt10n)-[2023.07.08|21:41:16(HKT)]
└> base64 -d flag.b64 | base64 -d | base64 -d | base64 -d | base64 -d | base64 -d | base64 -d | base64 -d | base64 -d | base64 -d | base64 -d | base64 -d | base64 -d | base64 -d
crew{Tru33333_Crypt_w1th_V014t1l1ty!}

You could write a script to automate it, but I’m lazy :D

Conclusion

What we’ve learned:

  1. Memory Forensic With Volatility
  2. Decrypting TrueCrypt Encrypted File