R4v!dus

Greatest Common Divisor

def gcd(m, n):
    if m < n:
        m,n = n, m
    if n == 0:
        return m
    if m % n == 0:
        return n
    else:
        return gcd(n, m%n)

def main():
    print(gcd(66528, 52920))   
    
if __name__ == "__main__":
	main()

def gcd(m,n):
    while n != 0:
       r = m%n
       (m,n) = (n,r)
    return abs(m)

def main():
    print(gcd(66528, 52920))   
    
if __name__ == "__main__":
	main()

MODULAR ARITHMETIC

def extended_gcd(a, b):
    if b > a:
        a, b = b, a
    if b == 0:
        return 0, 1  
    r = a % b
    print("a:{}, b:{}, r:{}".format(a, b, r))      
    v, u = extended_gcd(r, b)
    print("exit - a:{}, b:{}, v:{}, u:{}, r:{}".format(a, b, v, u, r))  
    return u - (a//b) * v, v


def main():  
    u, v = extended_gcd(26513, 32321)
    print("{}, {}".format(u, v))
    
if __name__ == "__main__":
	main()

Finding Flags

Great Snakes

#!/usr/bin/env python3

import sys
# import this

if sys.version_info.major == 2:
    print("You are running Python 2, which is no longer supported. Please update to Python 3.")

ords = [81, 64, 75, 66, 70, 93, 73, 72, 1, 92, 109, 2, 84, 109, 66, 75, 70, 90, 2, 92, 79]

print("Here is your flag:")
print("".join(chr(o ^ 0x32) for o in ords))

ASCII

a = [99, 114, 121, 112, 116, 111, 123, 65, 83, 67, 73, 73, 95, 112, 114, 49, 110, 116, 52, 98, 108, 51, 125]
result = ''
for i in range(0, len(a)):
    result += chr(a[i])    
print(result)​

Hex

a ='63727970746f7b596f755f77696c6c5f62655f776f726b696e675f776974685f6865785f737472696e67735f615f6c6f747d'
a = bytes.fromhex(a)
print(a)​

Base64

import base64

a = '72bca9b68fc16ac7beeb8f849dca1d8a783e8acf9679bf9269f7bf'
a = base64.b64encode(bytes.fromhex(a))
print(a)

Bytes and Big Integers

from Crypto.Util.number import *

a = 11515195063862318899931685488813747395775516287289682636499965282714637259206269
a = long_to_bytes(a)
print(a)

XOR Starter

a = "label"
result = ''

for c in a:
    result += chr(ord(c) ^ 13)

print(result)

XOR Properties

from Crypto.Util.number import *
import binascii

k1 = "a6c8b6733c9b22de7bc0253266a3867df55acde8635e19c73313"
k2_k1 = "37dcb292030faa90d07eec17e3b1c6d8daf94c35d4c9191a5e1e"
k2_k3 = "c1545756687e7573db23aa1c3452a098b71a7fbf0fddddde5fc1"
flag_k1_k3_k2 = "04ee9855208a2cd59091d04767ae47963170d1660df7f56f5faf"

result = long_to_bytes(bytes_to_long(binascii.unhexlify(flag_k1_k3_k2)) ^ bytes_to_long(binascii.unhexlify(k1)) ^ bytes_to_long(binascii.unhexlify(k2_k3)))

print(result)

Favourite byte

import binascii

a = '73626960647f6b206821204f21254f7d694f7624662065622127234f726927756d'
result=''

a = binascii.unhexlify(a)
for c in a:
    result += chr(c^(a[0]^ord('c')))
    
print(result)

You either know, XOR you don't

import binascii
from Crypto.Util.strxor import *
a = '0e0b213f26041e480b26217f27342e175d0e070a3c5b103e2526217f27342e175d0e077e263451150104'
key=''
result =''
# key 획득 및 유추
a = binascii.unhexlify(a)
key = strxor((a[:7]), b'crypto{')

# xor 연산
key = list('myXORkey')
for i in range(len(a)):
    result += chr(a[i] ^ ord(key[i%8]))

print(result)