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8 byte aligement in ISAKMP
When the ISAKMP packet is not 8 byte aligned, we pad it with zero's to make
it 8 byte aligned before we encrypt it during Oakley QM. Some packets
require that we calculate hash on the payloads so that the other end can
also authenticate us. When we calculate, do we also consider the padding? It
is better that we consider the padding as well as it will be easier to
verify on the other end. All we have to do is to calculate the length of the
data on which to calcuate hash is (payload_len - isakmp header_len - hash
payload_len - hash_data_len). We dont have to parse the ISAKMP payload to
find out the lenght of the data on which to calculate hash. That way, if the
hash fails we can drop the packet immediatly.
On the other hand, if we dont use the pad in calculating hash, then the last
byte of the hash should represent the lenght of the pad as that will help in
calculating the lenght of the data on which to calculate hash.
Comments?
Naganand
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