95 lines
2.7 KiB
Python
95 lines
2.7 KiB
Python
from cStringIO import StringIO
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import os
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from Crypto.Util import number
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flag = "wow_"
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def egcd(a, b):
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if a == 0:
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return (b, 0, 1)
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else:
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g, y, x = egcd(b % a, a)
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return (g, x - (b // a) * y, y)
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def modinv(a, m):
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g, x, y = egcd(a, m)
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if g != 1:
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raise Exception('modular inverse does not exist')
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else:
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return x % m
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def randleetify(s, random):
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i = list(s)
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for c in range(len(i)):
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if i[c] == 'i':
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if random.random() > 0.66:
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i[c] = '1'
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elif random.random() > 0.33:
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i[c] = 'I'
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elif i[c] == 'o':
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if random.random() > 0.66:
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i[c] = '0'
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elif random.random() > 0.33:
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i[c] = 'O'
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elif i[c] == 'a':
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if random.random() > 0.66:
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i[c] = '4'
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elif random.random() > 0.33:
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i[c] = 'A'
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elif i[c] == 'l':
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if random.random() > 0.66:
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i[c] = '1'
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elif random.random() > 0.33:
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i[c] = 'L'
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elif i[c] == 's':
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if random.random() > 0.66:
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i[c] = '5'
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elif random.random() > 0.33:
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i[c] = 'S'
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elif i[c] == 'e':
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if random.random() > 0.66:
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i[c] = '3'
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elif random.random() > 0.33:
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i[c] = 'E'
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elif i[c].isalpha():
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if random.random() > 0.5:
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i[c] = i[c].upper()
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return ''.join(i)
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def get_problem(random):
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n_length = 2048
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p = number.getPrime(n_length, os.urandom)
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q = number.getPrime(n_length, os.urandom)
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n = p*q
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e = 65537
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phi = (p-1)*(q-1)
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d = modinv(e, phi)
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cut = len(bin(d).strip('0b').strip('L'))//2 - 2
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given = bin(d).strip('0b').strip('L')[cut:]
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deez = hex(int(given,2)).zfill(len(given)/4)
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salt = randleetify("i_probably_shouldnta_leeked_d",random)
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return (n, e, cut, deez, salt)
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def generate_ciphertext(random):
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n, e, cut, deez, salt = get_problem(random)
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encoded = int(("easyctf{%s%s}" % (flag, salt)).encode('hex'),16)
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ciphertext = 'n: '+hex(n)+'\n'
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ciphertext += 'e: '+hex(e)+'\n'
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ciphertext += 'd: [??? '+str(cut)+' REDACTED BITS ???]'+str(deez)+'\n'
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ciphertext += 'c: '+hex(pow(encoded, e, n))+'\n'
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return StringIO(ciphertext)
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def generate(random):
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return dict(files={
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"ciphertext.txt": generate_ciphertext
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})
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def grade(random, key):
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n, e, cut, deez, salt = get_problem(random)
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if key.find("%s%s" % (flag, salt)) >= 0:
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return True, "Correct!"
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return False, "Nope."
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