Organisers ask us to NetCat chal.ctf.b01lers.com on Port 2008.

After connecting on the server we got some interfface like this one:


-----

There is 3 option called:
Method (which declare the method of encryption),
Ciphertext (which declare the encrypted text)
Input (this is a input field to submit decrypted text)

Organisers also provided a python script template which is:
```
# You can install these packages to help w/ solving unless you have others in mind
# i.e. python3 -m pip install {name of package}
from pwn import *
import codecs
from base64 import b64decode
from string import ascii_lowercase

HOST = ''
PORT = 0

r = remote(HOST,PORT)

def bacon(s):
# Do this

def rot13(s):
# And this

def atbash(s):
# And this one

def Base64(s):
# Lastly this one

if __name__ == '__main__':
count = 0
while True:
r.recvuntil('Method: ')
method = r.recvuntil('\n').strip()
r.recvuntil('Ciphertext: ')
argument = r.recvuntil('\n').strip()

result = globals()[method.decode()](argument.decode()) # :)

r.recv()
r.sendline(result.encode())
count += 1
if count == 1000:
print(r.recv())
exit(0)

```

If we read the code then we can understand that we need to decrypt 4 types of encryption which are:
1. [Bacon](https://en.wikipedia.org/wiki/Bacon%27s_cipher)
2. [ROT13](https://en.wikipedia.org/wiki/ROT13)
3. [Atbash](https://en.wikipedia.org/wiki/Atbash)
4. [Base64](https://en.wikipedia.org/wiki/Base64)

And we will get the flag ater 1000 times correct decryption.

so we just need to implement python decryption codes to the template.

After getting ready the python program, codes looks like this:
```
# You can install these packages to help w/ solving unless you have others in mind
# i.e. python3 -m pip install {name of package}
from pwn import *
import codecs
from base64 import b64decode
from string import ascii_lowercase

HOST = '104.197.187.199'
PORT = 2008

r = remote(HOST,PORT)

lookup = {'a':'AAAAA', 'b':'AAAAB', 'c':'AAABA', 'd':'AAABB', 'e':'AABAA',
'f':'AABAB', 'g':'AABBA', 'h':'AABBB', 'i':'ABAAA', 'j':'ABAAB',
'k':'ABABA', 'l':'ABABB', 'm':'ABBAA', 'n':'ABBAB', 'o':'ABBBA',
'p':'ABBBB', 'q':'BAAAA', 'r':'BAAAB', 's':'BAABA', 't':'BAABB',
'u':'BABAA', 'v':'BABAB', 'w':'BABBA', 'x':'BABBB', 'y':'BBAAA', 'z':'BBAAB'}

# Function to encrypt the string according to the cipher provided
def bacon(s):
decipher = ''
i = 0

# emulating a do-while loop
while True :
# condition to run decryption till
# the last set of ciphertext
if(i < len(s)-4):
# extracting a set of ciphertext
# from the message
substr = s[i:i + 5]
# checking for space as the first
# character of the substring
if(substr[0] != ' '):
'''
This statement gets us the key(plaintext) using the values(ciphertext)
Just the reverse of what we were doing in encrypt function
'''
decipher += list(lookup.keys())[list(lookup.values()).index(substr)]
i += 5 # to get the next set of ciphertext

else:
# adds space
decipher += ' '
i += 1 # index next to the space
else:
break # emulating a do-while loop

return decipher

def rot13(s):
chars = "abcdefghijklmnopqrstuvwxyz"
trans = chars[13:]+chars[:13]
rot_char = lambda c: trans[chars.find(c)] if chars.find(c)>-1 else c
return ''.join( rot_char(c) for c in s )

lookup_table = {'a' : 'z', 'b' : 'y', 'c' : 'x', 'd' : 'w', 'e' : 'v',
'f' : 'u', 'g' : 't', 'h' : 's', 'i' : 'r', 'j' : 'q',
'k' : 'p', 'l' : 'o', 'm' : 'n', 'n' : 'm', 'o' : 'l',
'p' : 'k', 'q' : 'j', 'r' : 'i', 's' : 'h', 't' : 'g',
'u' : 'f', 'v' : 'e', 'w' : 'd', 'x' : 'c', 'y' : 'b', 'z' : 'a'}

def atbash(s):
cipher = ''
for letter in s:
# checks for space
if(letter != ' '):
#adds the corresponding letter from the lookup_table
cipher += lookup_table[letter]
else:
# adds space
cipher += ' '

return cipher

def Base64(s):
decodedBytes = base64.b64decode(s)
decodedStr = str(decodedBytes)
return (decodedStr)

if __name__ == '__main__':
count = 0
while True:
r.recvuntil('Method: ')
method = r.recvuntil('\n').strip()
r.recvuntil('Ciphertext: ')
argument = r.recvuntil('\n').strip()

result = globals()[method.decode()](argument.decode()) # :)

r.recv()
r.sendline(result.encode())
count += 1
if count == 1000:
print(r.recv())
exit(0)

```

After run this program we got the Flag:
> We must be dreaming, here's your flag: ctf{4n_313g4nt_s01ut10n_f0r_tr4cking_r341ity}

Original writeup (https://abbishal.me/).