easyctf-2017/rsa2/grader.py
2017-03-14 01:20:41 -05:00

48 lines
1.4 KiB
Python

from cStringIO import StringIO
flag = "l0w_n"
def modx(base,exp,mod):
r = 1;
while (exp > 0):
if (exp % 2 == 1):
r = (r * base) % mod
base = (base * base) % mod
exp = exp/2
return r
def probprime(s):
if s%2==0:
s += 1
smolprimes = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97]
while len(set([modx(i,s-1,s) for i in smolprimes])) != 1 or modx(2,s-1,s) != 1:
s+=2
return(s)
def get_problem(random):
# add Probable Prime function later
p = probprime(random.randint(10**20,9*10**20))
q = probprime(random.randint(10**20,9*10**20))
e = 65537
salt = "".join([random.choice("0123456789abcdef") for i in range(4)])
return (p, q, e, salt)
def generate_ciphertext(random):
p, q, e, salt = get_problem(random)
encoded = int(("flag{%s_%s}" % (flag, salt)).encode('hex'),16)
ciphertext = 'n: '+str(p*q)+'\n'
ciphertext += 'e: '+str(e)+'\n'
ciphertext += 'c: '+str(pow(encoded, e, p*q))+'\n'
return StringIO(ciphertext)
def generate(random):
return dict(files={
"ciphertext2.txt": generate_ciphertext
})
def grade(random, key):
p, q, e, salt = get_problem(random)
if key.find("%s_%s" % (flag, salt)) >= 0:
return True, "Correct!"
return False, "Nope."