Remove dependency on pycryptodome (#17)

* Remove dependancy on PyCryptodome (Martin's code)

* Minor fix to signature verification

* Update setup.py

licensing/internal.py

@@ -5,9 +5,6 @@
 @author: Artem Los
 """
 import base64
-from Crypto.Signature import PKCS1_v1_5
-from Crypto.Hash import SHA256
-from Crypto.PublicKey import RSA
 import urllib.request
 import hashlib
 from subprocess import Popen, PIPE
@@ -23,16 +20,67 @@ def get_SHA256(string):
         """
         return hashlib.sha256(string.encode("utf-8")).hexdigest()
 
+    @staticmethod
+    def I2OSP(x, xLen):
+        if x > (1 << (8 * xLen)):
+            return None
+        Xrev = []
+        for _ in range(0, xLen):
+            x, m = divmod(x, 256)
+            Xrev.append(m)
+        return bytes(reversed(Xrev))
+
+    @staticmethod
+    def OS2IP(X):
+        import binascii
+        h = binascii.hexlify(X)
+        return int(h, 16)
+
+    @staticmethod
+    def RSAVP1(pair, s):
+        n, e = pair
+        if s < 0 or n-1 < s:
+            return None
+        return pow(s, e, n)
+
+    @staticmethod
+    def EMSA_PKCS1_V15_ENCODE(M, emLen):
+        import hashlib
+        h = hashlib.sha256()
+        h.update(M)
+        H = h.digest()
+
+        T = bytes([0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, 0x05, 0x00, 0x04, 0x20]) + H
+        tLen = len(T)
+        if emLen < tLen + 11:
+            return None
+        PS = bytes([0xff for _ in range(emLen - tLen - 3)])
+        return b"".join([b"\x00\x01", PS, b"\x00", T])
+
+    @staticmethod
+    def RSAASSA_PKCS1_V15_VERIFY(pair, M, S):
+        n, e = pair
+        s = HelperMethods.OS2IP(S)
+        m = HelperMethods.RSAVP1((n,e), s)
+        if m is None: return False
+        EM = HelperMethods.I2OSP(m, 256)
+        if EM is None: return False
+        EM2 = HelperMethods.EMSA_PKCS1_V15_ENCODE(M, 256)  # Can return None, but it's OK since EM is not None
+        return EM == EM2
+
     @staticmethod
     def verify_signature(response, rsaPublicKey):       
         """
         Verifies a signature from .NET RSACryptoServiceProvider.
         """
-        cryptoPubKey = RSA.construct((HelperMethods.base642int(rsaPublicKey.modulus),\
-                                      HelperMethods.base642int(rsaPublicKey.exponent)))
-        h = SHA256.new(base64.b64decode(response.license_key.encode("utf-8")))
-        verifier = PKCS1_v1_5.new(cryptoPubKey)
-        return verifier.verify(h, base64.b64decode(response.signature.encode("utf-8")))
+
+        n = HelperMethods.OS2IP(base64.b64decode(rsaPublicKey.modulus))
+        e = HelperMethods.OS2IP(base64.b64decode(rsaPublicKey.exponent))
+
+        m = base64.b64decode(response.license_key)
+        r = base64.b64decode(response.signature)
+
+        return HelperMethods.RSAASSA_PKCS1_V15_VERIFY((n,e), m, r)
 
     @staticmethod
     def int2base64(num):

setup.py

@@ -2,17 +2,14 @@
 setup(
   name = 'licensing',         # How you named your package folder (MyLib)
   packages = ['licensing'],   # Chose the same as "name"
-  version = '0.12',      # Start with a small number and increase it with every change you make
+  version = '0.13',      # Start with a small number and increase it with every change you make
   license='MIT',        # Chose a license from here: https://help.github.com/articles/licensing-a-repository
   description = 'Client library for Cryptolens licensing Web API.',   # Give a short description about your library
   author = 'Cryptolens AB',                   # Type in your name
   author_email = 'support@cryptolens.io',      # Type in your E-Mail
   url = 'https://cryptolens.io',   # Provide either the link to your github or to your website
-  download_url = 'https://github.com/Cryptolens/cryptolens-python/archive/v_12.tar.gz',    # I explain this later on
+  download_url = 'https://github.com/Cryptolens/cryptolens-python/archive/v_13.tar.gz',    # I explain this later on
   keywords = ['software licensing', 'licensing library', 'cryptolens'],   # Keywords that define your package best
-  install_requires=[            # I get to this in a second
-          'pycryptodome'
-      ],
   classifiers=[
     #'Development Status :: 5 - Stable',      # Chose either "3 - Alpha", "4 - Beta" or "5 - Production/Stable" as the current state of your package
     'Intended Audience :: Developers',      # Define that your audience are developers