# ASISCTF 2021

***Note : A JOURNEY TO GAIN KNOWLEDGE***

## ***#Warmup***

```
#!/usr/bin/env python3
 
from Crypto.Util.number import *
import string
from secret import is_valid, flag
 
def random_str(l):
    rstr = ''
    for _ in range(l):
        rstr += string.printable[:94][getRandomRange(0, 93)]
    return rstr
 
def encrypt(msg, nbit):
    l, p = len(msg), getPrime(nbit)
    rstr = random_str(p - l)
    msg += rstr
    while True:
        s = getRandomNBitInteger(1024)
        if is_valid(s, p):
            break
    enc = msg[0]
    for i in range(p-1):
        enc += msg[pow(s, i, p)]
    return enc
 
nbit = 15
enc = encrypt(flag, nbit)
print(f'enc = {enc}')
```

[output.txt](https://github.com/GiongfNef/ChallFile/blob/main/ASISCTF2021/output.txt)

\#Solve

```
with open('output.txt') as f:
    enc = f.read()[6:]
p = len(enc)
print(enc)
for s in range(9900,p-1):
# maybe you can find ASIS{_how_dFC.YptZTh1S?h0mx_m4d;_lGD_w;dr\_CUYpI0_5J2T3+?k!!!*Z} when s = 8562 but it stil wrong
# the correct one is ASIS{_how_d3CrYpt_Th1S_h0m3_m4dE_anD_wEird_CrYp70_5yST3M?!!!!!!} when s = 10927
    flag = ['']*p
    for i in range(p-1):
        flag[pow(s, i, p)] = enc[i+1]
         
    flag = 'A' + ''.join(flag)
    flag = flag.encode()
    if b'ASIS' in flag:
        print(flag)
        break
    print(s)
```

Thanks for reading. Have a nice day <3 .


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://giongfnef.gitbook.io/ctf-2021/ctf2021-2/asisctf-2021.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.