Remove OpenSSL support; only support PyCryptodome

This allows us to clean up the code a lot.

On Windows, it isn't installed by default and
most of the time not be found at all.

On M1 Macs, the kernel will kill the process instead.

Closes #33.

DeDRM_plugin/adobekey_get_passhash.py

@@ -23,20 +23,13 @@ import sys, os, time
 import base64, hashlib
 try: 
     from Cryptodome.Cipher import AES
-except:
+    from Cryptodome.Util.Padding import unpad
+except ImportError:
     from Crypto.Cipher import AES
+    from Crypto.Util.Padding import unpad
 
 PASS_HASH_SECRET = "9ca588496a1bc4394553d9e018d70b9e"
 
-def unpad(data):
-
-    if sys.version_info[0] == 2:
-        pad_len = ord(data[-1])
-    else:
-        pad_len = data[-1]
-
-    return data[:-pad_len]
-
 
 try:
     from calibre.constants import iswindows, isosx
@@ -55,7 +48,7 @@ def decrypt_passhash(passhash, fp):
     hash_key = hashlib.sha1(bytearray.fromhex(serial_number + PASS_HASH_SECRET)).digest()[:16]
 
     encrypted_cc_hash = base64.b64decode(passhash)
-    cc_hash = unpad(AES.new(hash_key, AES.MODE_CBC, encrypted_cc_hash[:16]).decrypt(encrypted_cc_hash[16:]))
+    cc_hash = unpad(AES.new(hash_key, AES.MODE_CBC, encrypted_cc_hash[:16]).decrypt(encrypted_cc_hash[16:]), 16)
     return base64.b64encode(cc_hash).decode("ascii")