libwifi: make decrpyt_ccmp more robust

It should not also work if the provided packet contains a Dot11WEP
packet for some reason.

krackattack/libwifi/crypto.py

@@ -108,7 +108,7 @@ def decrypt_ccmp(p, tk, verify=True):
 	p = p.copy()
 
 	# Get used CCMP parameters
-	keyid = p.key_id
+	keyid = get_ccmp_keyid(p)
 	priority = dot11_get_priority(p)
 	pn = dot11ccmp_get_pn(p)
 

krackattack/libwifi/wifi.py

@@ -354,6 +354,11 @@ def dot11_get_priority(p):
 
 #### Crypto functions and util ####
 
+def get_ccmp_keyid(p):
+	if Dot11WEP in p:
+		return p.keyid
+	return p.key_id
+
 def get_ccmp_payload(p):
 	if Dot11WEP in p:
 		# Extract encrypted payload: