TMCTF Qualification Round 2015 - Crypto 300
Description for this challenge was:
What is the most famous default password of "keystore"?
along with the provided password protected file level1.zip.
Googling for famous default password keystore gave us the following entry at the first page of results:
Setting a Keystore Password - JXplorer (jxplorer.org/help/Setting_a_Keystore_Password.htm)
The cacerts keystore file has a default password of changeit; the clientcerts keystore file has a default password of passphrase. This option allows you to set a ...
Trying to open the password protected file level1.zip with the password changeit was a success. Inside of it there were three files:
level2.file.encrypted
level2.key.encrypted
Readme.txt
Content of file Readme.txt was as follows:
Welcome to the published key quest!
Your Quest is to find the published key!
You have a encrypted file and a encrypted key.
- levelX.file.encrypted
- levelX.key.encrypted
If you can find the key for decrypting "levelX.key.encrypted", then you can decrypt the file.
We encrypted the file using the following command.
>openssl enc -aes-256-cbc -salt -base64 -in ./levelX+1.zip -out levelX.file.encrypted -pass file:./levelX.key
We also encrypted the key using the following command.
>openssl rsautl -encrypt -inkey ThePublishedPublicKey.pem -pubin -in levelX.key | openssl base64 >levelX.key.encrypted
If you can decrypt "levelX.file.encrypted", you can get a next level zip file.
All zip files are encrypted by the level 1 quest's answer.
========================================================================
Level 2 quest's hint :
The key of the most famous "Snakeoil" CA.
========================================================================
Have fun!
Googling for Snakeoil CA ext:key resulted with the following entry at the first page:
libapache-mod-ssl/snakeoil-ca-rsa.key at master ... - GitHub (https://github.com/...mod-ssl/.../snakeoil-ca-rsa.key)
Contribute to libapache-mod-ssl development by creating an account on GitHub.
Using that same file to decrypt the Level2 files produced the following results:
$ wget https://raw.githubusercontent.com/ByteInternet/libapache-mod-ssl/master/pkg.sslcfg/snakeoil-ca-rsa.key
--2015-09-29 14:09:00-- https://raw.githubusercontent.com/ByteInternet/libapache-mod-ssl/master/pkg.sslcfg/snakeoil-ca-rsa.key
Resolving raw.githubusercontent.com (raw.githubusercontent.com)... 23.235.43.133
Connecting to raw.githubusercontent.com (raw.githubusercontent.com)|23.235.43.133|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 887 [text/plain]
Saving to: ‘snakeoil-ca-rsa.key’
100%[===================================================================================================================================================================================================>] 887 --.-K/s in 0s
2015-09-29 14:09:00 (369 MB/s) - ‘snakeoil-ca-rsa.key’ saved [887/887]
$ PASS=$(cat level2.key.encrypted | base64 -d | openssl rsautl -decrypt -inkey snakeoil-ca-rsa.key)
$ openssl enc -d -aes-256-cbc -salt -base64 -in level2.file.encrypted -out level2.file -pass pass:$PASS
$ file level2.file
level2.file: Zip archive data, at least v2.0 to extract
$ mv level2.file level2.zip
Unzipping the level2.zip with the (reused) password changeit resulted with the following three files:
level3.file.encrypted
level3.key.encrypted
Readme.txt
Content of Readme.txt was as follows:
========================================================================
Level 3 quest's hint :
-This RSA key is intended for testing the most popular packet analyzer.
-Prime1 < Prime2
========================================================================
Have fun!
By visiting the (most popular packet analyzer) Wireshark's Github repository (https://github.com/wireshark/wireshark), we found the following files inside the directory /test/keys:
dhe1_keylog.dat add a test for SSL/TLS decryption using the master secret
key.p12 SSL: Add support for private key password when decrypting
rsa-p-lt-q.key ssl-utils: fix failing decryption for some RSA keys
rsasnakeoil2.key Remove svn:executable attribute.
snakeoil-rsa.key Add a test for DTLS decryption.
As the hint says Prime1 < Prime2 by using the rsa-p-lt-q.key we got the following results:
$ wget https://raw.githubusercontent.com/wireshark/wireshark/master/test/keys/rsa-p-lt-q.key
--2015-09-29 14:09:41-- https://raw.githubusercontent.com/wireshark/wireshark/master/test/keys/rsa-p-lt-q.key
Resolving raw.githubusercontent.com (raw.githubusercontent.com)... 185.31.19.133
Connecting to raw.githubusercontent.com (raw.githubusercontent.com)|185.31.19.133|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 887 [text/plain]
Saving to: ‘rsa-p-lt-q.key’
100%[===================================================================================================================================================================================================>] 887 --.-K/s in 0s
2015-09-29 14:09:41 (474 MB/s) - ‘rsa-p-lt-q.key’ saved [887/887]
$ PASS=$(cat level3.key.encrypted | base64 -d | openssl rsautl -decrypt -inkey rsa-p-lt-q.key)
$ openssl enc -d -aes-256-cbc -salt -base64 -in level3.file.encrypted -out level3.file -pass pass:$PASS
$ file level3.file
level3.file: Zip archive data, at least v2.0 to extract
$ mv level3.file level3.zip
Unzipping the level3.zip with the (reused) password changeit resulted with the following three files:
level4.file.encrypted
level4.key.encrypted
Readme.txt
Content of Readme.txt was as follows:
========================================================================
Level 4 quest's hint :
-This RSA key is intended for testing the most famous implementation of Python.
-This published key is password-encrypted, and you may also have to find the password.
-SHA1 hash for the encrypted key is 81754334cd36efd8ac0664ef78f92be4b1f9f4ac.
========================================================================
Have fun!
By visiting the (most famous implementation of Python) CPython's Github repository (https://github.com/python/cpython), we found the file ssl_key.pem inside the directory /Lib/test. Using it we got the following results:
$ wget https://raw.githubusercontent.com/python/cpython/master/Lib/test/ssl_key.pem
--2015-09-29 14:19:36-- https://raw.githubusercontent.com/python/cpython/master/Lib/test/ssl_key.pem
Resolving raw.githubusercontent.com (raw.githubusercontent.com)... 23.235.43.133
Connecting to raw.githubusercontent.com (raw.githubusercontent.com)|23.235.43.133|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 916 [text/plain]
Saving to: ‘ssl_key.pem’
100%[===================================================================================================================================================================================================>] 916 --.-K/s in 0s
2015-09-29 14:19:36 (378 MB/s) - ‘ssl_key.pem’ saved [916/916]
$ PASS=$(cat level4.key.encrypted | base64 -d | openssl rsautl -decrypt -inkey ssl_key.pem)
$ openssl enc -d -aes-256-cbc -salt -base64 -in level4.file.encrypted -out level4.file -pass pass:$PASS
$ file level4.file
level4.file: Zip archive data, at least v2.0 to extract
$ mv level4.file level4.zip
Unzipping the level4.zip with the (reused) password changeit resulted with the following three files:
level5.file.encrypted
level5.key.encrypted
Readme.txt
Content of Readme.txt was as follows:
========================================================================
Level 5 quest's hint :
The key is one of the keys related to a famous vulnerable random generator.
========================================================================
Have fun!
By Googling for famous vulnerable random generator we've seen that there are references to the Debian OpenSSL Bug. Hence, by Googling for Debian OpenSSL keys we were being brought to the Debian OpenSSL Predictable PRNG Github repository (https://github.com/g0tmi1k/debian-ssh). By using its collection of predictable SSH/RSA private keys in a brute-force manner we got the following results:
$ wget https://github.com/g0tmi1k/debian-ssh/raw/master/common_keys/debian_ssh_rsa_2048_x86.tar.bz2
--2015-09-29 14:30:37-- https://github.com/g0tmi1k/debian-ssh/raw/master/common_keys/debian_ssh_rsa_2048_x86.tar.bz2
Resolving github.com (github.com)... 192.30.252.131
Connecting to github.com (github.com)|192.30.252.131|:443... connected.
HTTP request sent, awaiting response... 302 Found
Location: https://raw.githubusercontent.com/g0tmi1k/debian-ssh/master/common_keys/debian_ssh_rsa_2048_x86.tar.bz2 [following]
--2015-09-29 14:30:38-- https://raw.githubusercontent.com/g0tmi1k/debian-ssh/master/common_keys/debian_ssh_rsa_2048_x86.tar.bz2
Resolving raw.githubusercontent.com (raw.githubusercontent.com)... 23.235.43.133
Connecting to raw.githubusercontent.com (raw.githubusercontent.com)|23.235.43.133|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 50226987 (48M) [application/octet-stream]
Saving to: ‘debian_ssh_rsa_2048_x86.tar.bz2’
100%[===================================================================================================================================================================================================>] 50.226.987 2,26MB/s in 21s
2015-09-29 14:31:01 (2,26 MB/s) - ‘debian_ssh_rsa_2048_x86.tar.bz2’ saved [50226987/50226987]
$ tar xjf debian_ssh_rsa_2048_x86.tar.bz2
$ cat level5.key.encrypted | base64 -d > level5.key.raw
$ for i in $(find ./rsa/2048/ -iname "*"); do openssl rsautl -decrypt -inkey $i -in level5.key.raw >> brute_results.txt; echo >> brute_results.txt; done 2>/dev/null
$ sort -u brute_results.txt # to trim the blank lines
WZIj2mhQmOsp8A26hqVlRC6aLoB94+9yNWATCTnWzwo=
$ PASS="WZIj2mhQmOsp8A26hqVlRC6aLoB94+9yNWATCTnWzwo="
$ openssl enc -d -aes-256-cbc -salt -base64 -in level5.file.encrypted -out level5.file -pass pass:$PASS
$ file level5.file
level5.file: Zip archive data, at least v2.0 to extract
$ mv level5.file level5.zip
Unzipping the level5.zip with the (reused) password changeit resulted with the following file:
flag.txt
Content of flag.txt was as follows:
Congratulations!
This is the final quest.
TMCTF{Anyway, don't use (disclosed|default) keys:)}
Hence, the final flag was:
TMCTF{Anyway, don't use (disclosed|default) keys:)}
-stamparm
Written on September 29, 2015