easyctf-2017/RSA1/grader.py

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from cStringIO import StringIO
flag = "wh3n_y0u_h4ve_p&q_RSA_iz_ez"
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):
while (modx(2,s-1,s) != 1 or modx(3,s-1,s) != 1 or modx(5,s-1,s) != 1 or modx(7,s-1,s) != 1):
s += 1
return(s)
def get_problem(random):
# add Probable Prime function later
2017-03-04 23:04:37 +00:00
p = probprime(random.randint(3*10**59,4*10**59))
q = probprime(random.randint(3*10**59,4*10**59))
e = 3
salt = "".join([random.choice("0123456789abcdef") for i in range(8)])
return (p, q, e, salt)
def generate_ciphertext(random):
p, q, e, salt = get_problem(random)
encoded = int(("easyctf{%s_%s}" % (flag, salt)).encode('hex'),16)
ciphertext = 'p: '+str(p)+'\n'
ciphertext += 'q: '+str(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={
"ciphertext_rsa1.txt": generate_ciphertext
})
def grade(random, key):
n, salt = get_problem(random)
if key.find("%s_%s" % (flag, salt)) >= 0:
return True, "Correct!"
return False, "Nope."