Add a 16-bit token index into the anti-clogging token. This can be used
to enforce only a single use of each issued anti-clogging token request.
The token value is now token-index |
last-30-octets-of(HMAC-SHA256(sae_token_key, STA-MAC-address |
token-index)), i.e., the first two octets of the SHA256 hash value are
replaced with the token-index and token-index itself is protected as
part of the HMAC context data.
Track the used 16-bit token index values and accept received tokens only
if they use an index value that has been requested, but has not yet been
used. This makes it a bit more difficult for an attacker to perform DoS
attacks against the heavy CPU operations needed for processing SAE
commit since the attacker cannot simply replay the same frame multiple
times and instead, needs to request each token separately.
While this does not add significant extra processing/CPU need for the
attacker, this can be helpful in combination with the queued processing
of SAE commit messages in enforcing more delay during flooding of SAE
commit messages since the new anti-clogging token values are not
returned before the new message goes through the processing queue.
Signed-off-by: Jouni Malinen <jouni@codeaurora.org>
a9af1da0b5