在python中使用rsa加密时处理零

Question

I have been given a word "NETLAB" and have been told to encrypt it the following way by giving each letter a two-digit positional code, so this then becomes 14, 05, 20, 12, 01, 02. The next step is to deal with these in 3 blocks on 4 digits so they become 1405, 2012 and 0102, I can encrypt and decrypt the first two fine, however, I have run into a problem trying to encrypt and decrypt with '0102', I am pretty certain this is due to the number starting with 0 and that with it being an int the 0 is disregarded, which does not help when encrypting/decrypting data. So my question is how do I either stop the 0 from being disregarded? I have tried putting all the number into an array then concatenating them but I run into problems when using lists and powers of calculations. My code is below:

from __future__ import division
import fractions
import itertools
import urllib2

ml = []
p = 47
q = 59
x = 2
d = 0
e = 0


z = (p-1)*(q-1)
print z
n = p*q
print n

for x in range(z):
    if (fractions.gcd(x, z) == 1):
        ml.append(x)
    ##print ml

s = 2
for s,x in itertools.product(range(65),ml):
    t = s * x 
    if t == z + 1:
        ##print s
        ##print x
        break
d = x
e = s
print d
print e

med = []
message = "NETLAB"
for c in message:
    m = ord(c) - 64
    m = ("%02d" % m)
    med.append(m)
    print m

print "m^e(mod n)"

A = med.join(0, 1)
##B = 
##C = 


Ea = A ** e % n
##Eb = B ** e % n
##Ec = C ** e % n 

print Ea
##print Eb
##print Ec


print "Ea^d(mod n)"
Da = Ea ** d % n
##Db = Eb ** d % n
##Dc = Ec ** d % n

print Da
##print Db
##print Dc

Answer 1

I think this all depends on what you mean by the leading 0 being "disregarded". When you apply the following expression, you're implying that A is an integer:

Ea = A ** e % n

In positional notation leading zeros have no value, but this does not mean they are being disregarded. The integer 0102 will always have the value of 102, whereas for any other x, x102 will not have the value 102.

As for the output (let's say you were writing this to a file, or some other encoding where the leading 0 is important), then it's simply a matter of formatting. For example, you could try the following function:

def encrypt_decrypt(m,d,e,n):
    print "m           %4s" % m

    Ea = (int(m) ** e) % n
    print "Ea          %d" % Ea

    Da = (Ea ** d) % n
    print "Ea^d(mod n) %04d" % Da

Calling this function with

encrypt_decrypt(''.join(med[0:2]),d,e,n)
encrypt_decrypt(''.join(med[2:4]),d,e,n)
encrypt_decrypt(''.join(med[4:6]),d,e,n)

Gives the output

m           1405
Ea          2641
Ea^d(mod n) 1405
m           2012
Ea          1453
Ea^d(mod n) 2012
m           0102
Ea          1395
Ea^d(mod n) 0102

(Note that I used the following...

p = 47
q = 59
x = 2
d = 5
e = 0

...)