Tags: cryptography crypto decode
Rating:
## Description
* **Name:** [School](https://2019.peactf.com/problems)
* **Points:** 100
* **Tag:** Crypto
## Tools
* Firefox Version 60.8.0 https://www.mozilla.org/en-US/firefox/60.8.0/releasenotes/
* Alphabetical Substitution https://www.dcode.fr/ascii-code
* Cryptovenom https://github.com/lockedbyte/cryptovenom
## Writeup
Download the file called enc.txt (4fc5d4517a98bd97fede504d6f5e42bc) through the link where we find a cipher text.
```bash
root@1v4n:~/CTF/peaCTF2019/crypto/School# wget https://shell1.2019.peactf.com/static/6999a90c2dc921d2e0de4720df921549/enc.txt
root@1v4n:~/CTF/peaCTF2019/crypto/School# md5sum enc.txt
e0aee564db0a8f5f26118817784859ef enc.txt
root@1v4n:~/CTF/peaCTF2019/crypto/School# file enc.txt
enc.txt: UTF-8 Unicode text
root@1v4n:~/CTF/peaCTF2019/crypto/School# cat enc.txt
Alphabet: WCGPSUHRAQYKFDLZOJNXMVEBTI
zswGXU{ljwdhsqmags}
```
We use the AS online tool to decipher the message >
or with Cryptovenom python tool
```bash
root@1v4n:~/CTF/peaCTF2019/crypto/School# git clone https://github.com/lockedbyte/cryptovenom.git
root@1v4n:~/CTF/peaCTF2019/crypto/School/cryptovenom# python2 cryptovenom.py
▄▄· ▄▄▄ ▄· ▄▌ ▄▄▄·▄▄▄▄▄ ▌ ▐·▄▄▄ . ▐ ▄ • ▌ ▄ ·.
▐█ ▌▪▀▄ █·▐█▪██▌▐█ ▄█•██ ▪ ▪█·█▌▀▄.▀·•█▌▐█▪ ·██ ▐███▪
██ ▄▄▐▀▀▄ ▐█▌▐█▪ ██▀· ▐█.▪ ▄█▀▄ ▐█▐█•▐▀▀▪▄▐█▐▐▌ ▄█▀▄ ▐█ ▌▐▌▐█·
▐███▌▐█•█▌ ▐█▀·.▐█▪·• ▐█▌·▐█▌.▐▌ ███ ▐█▄▄▌██▐█▌▐█▌.▐▌██ ██▌▐█▌
·▀▀▀ .▀ ▀ ▀ • .▀ ▀▀▀ ▀█▄▀▪. ▀ ▀▀▀ ▀▀ █▪ ▀█▄▀▪▀▀ █▪▀▀▀
...
-[MENU]-
...
4) Classical Algorithms
...
[=] Option: 4
...
-[MENU:Classical]-
...
11) Simple Substitution Cipher
...
[=] Option: 11
...
-=[OPTIONS]=-
...
2) Decrypt
...
[=] Option: 2
[=] [F]ile or [T]ext: T
[=] Text: zswGXU{ljwdhsqmags}
[=] Output format (Eg.: raw or base64): raw
[=] Key: WCGPSUHRAQYKFDLZOJNXMVEBTI
[+] Out = PEACTFORANGEJUICE
[+] All done!
```
and also you can use the [pycipher module](https://pypi.org/project/pycipher/)
```python
>>> from pycipher import SimpleSubstitution
>>> ss = SimpleSubstitution('wcgpsuhraqykfdlzojnxmvebti')
>>> ss.decipher('zswGXU{ljwdhsqmags}')
'PEACTFORANGEJUICE'
````
### Flag
```bash
___ ____ ____ _ __ __ _
_ ___ ____ ___ _ ,"___"./_ _\ F ___J ."_J ____ _ ___ ___ _ _ ___ ___ _ ____ LJ _ _ LJ ____ ____ F_".
J '__ J F __ J F __` L FJ---L][J L]J |___: _/ /-' F __ J J '__ ",F __` L J '__ J F __` L F __ J _ J | | L F ___J. F __ J '-\ \_
| |--| | | _____J | |--| |J | LJ | | | _____|_ (/ | |--| | | |__|-| |--| | | |__| | | |--| | | _____J J J | | | | FJ | |---LJ | _____J \) _|
F L__J J F L___--.F L__J J| \___--.F J F |____L_L."-__ F L__J J F L `-F L__J J F L J J F L__J J F L___--. J LF L__J JJ LF L___--.F L___--.__-".J_J
J _____/J\______/J\____,__J\_____/J____J__F "_"-__J\______/J__L J\____,__J__L J__L)-____ J\______/,-_J J\____,__J__J\______/J\______/J__-"_"
|_J_____F J______F J____,__FJ_____F|____|__| "-__|J______F|__L J____,__|__L J__J\______/FJ______F\_____/J____,__|__|J______F J______F|__-"
L_J J______F \_____/
```
