In the process, I learned a new simple Python fact: the
pow function (which is now a built-in), can take a modulus as a third argument. And, it works where this doesn't seem to: (x**y) % z
(I discovered this by digging into the rsa module source).
python -m timeit -s "import rsa; \
f = open('id_rsa'); data = f.read(); f.close(); k = rsa.PrivateKey.load_pkcs1(data)"\
"41330915578951772302369**k.e % k.n"
10000 loops, best of 3: 79.4 usec per loop
python -m timeit -s "import rsa; \
f = open('id_rsa'); data = f.read(); f.close(); k = rsa.PrivateKey.load_pkcs1(data)"\
"pow(41330915578951772302369, k.e, k.n)"
10000 loops, best of 3: 70.2 usec per loop |
In the example here, both work and have about the same timing. But in the code below, the first version hangs when doing decryption (with a large base). Here's the output, followed by the script.
> python encode.py m: Hello, secret world! p: .xyz.Hello, secret world!.xyz. a: 413309155789517723023698766343791993289928631329 c: 11434905702482726455415220687715293368262190253795 .. i: 413309155789517723023698766343791993289928631329 r: Hello, secret world! |
encode.pyimport rsa
with open('id_rsa') as f:
data = f.read()
k = rsa.PrivateKey.load_pkcs1(data)
n = k.n
e = k.e
d = k.d
def my_atoi(s):
L = [ord(c) for c in s]
k = 256
iL = L[:]
iL.reverse()
x = iL[0]
for i in iL[1:]:
x += i*k
k *= 256
return x
def my_itoa(i):
rL = list()
while i:
rL.append(i%256)
i = i/256
rL.reverse()
return ''.join([chr(n) for n in rL])
def encrypt(m):
return m**e % n
def decrypt(c):
# note: c**d % n fails
return pow(c,d,n)
if __name__ == '__main__':
m = 'Hello, secret world!'
pad = '.xyz.'
p = pad + m + pad
a = my_atoi(m)
c = encrypt(a)
i = decrypt(c)
r = my_itoa(i)
r = r.replace(pad,'')
L = zip('mpacir',[m,p,a,c,i,r])
N = 50
for varname, var in L:
s = str(var)
print varname + ': ', s[:N],
if len(s) > N: print '..'
else: print |
