Tolerate installation of pycryptodome

Newer versions of pysaml2 uses pycryptodome, so if by
accident if this library gets installed, Nova breaks.

paramiko folks are working on this:
https://github.com/paramiko/paramiko/issues/637

In the meanwhile, we should tolerate if either pycrypto
or pycryptodome is installed.

Closes-Bug: #1545370
Change-Id: If88beeb3983705621fe736995939ac20b2daf1f3

nova/crypto.py

@@ -26,6 +26,7 @@ import base64
 import binascii
 import os
 
+from Crypto.PublicKey import RSA
 from cryptography import exceptions
 from cryptography.hazmat import backends
 from cryptography.hazmat.primitives.asymmetric import padding
@@ -161,8 +162,27 @@ def generate_x509_fingerprint(pem_key):
                      'Error message: %s') % ex)
 
 
+def generate_key(bits):
+    """Generate a paramiko RSAKey"""
+    # NOTE(dims): pycryptodome has changed the signature of the RSA.generate
+    # call. specifically progress_func has been dropped. paramiko still uses
+    # pycrypto. However some projects like latest pysaml2 have switched from
+    # pycrypto to pycryptodome as pycrypto seems to have been abandoned.
+    # paramiko project has started transition to pycryptodome as well but
+    # there is no release yet with that support. So at the moment depending on
+    # which version of pysaml2 is installed, Nova is likely to break. So we
+    # call "RSA.generate(bits)" which works on both pycrypto and pycryptodome
+    # and then wrap it into a paramiko.RSAKey
+    rsa = RSA.generate(bits)
+    key = paramiko.RSAKey(vals=(rsa.e, rsa.n))
+    key.d = rsa.d
+    key.p = rsa.p
+    key.q = rsa.q
+    return key
+
+
 def generate_key_pair(bits=2048):
-    key = paramiko.RSAKey.generate(bits)
+    key = generate_key(bits)
     keyout = six.StringIO()
     key.write_private_key(keyout)
     private_key = keyout.getvalue()

nova/tests/unit/test_crypto.py

@@ -361,7 +361,7 @@ class KeyPairTest(test.NoDBTestCase):
         keyin.seek(0)
         key = paramiko.RSAKey.from_private_key(keyin)
 
-        with mock.patch.object(paramiko.RSAKey, 'generate') as mock_generate:
+        with mock.patch.object(crypto, 'generate_key') as mock_generate:
             mock_generate.return_value = key
             (private_key, public_key, fingerprint) = crypto.generate_key_pair()
             self.assertEqual(self.rsa_pub, public_key)