Wireless Security
- Integrity Attacks
Integrity of the
information is a characteristic that ensures that data was not tampered, when
going from point A to point B over the network (either wireless or wired). When
speaking about wireless communication, 802.11 radios can be overheard by any 3rd party on the
same frequency channel. A simple type of attack against integrity of the
information is illustrated in the following diagram
Let's imagine that legitimate wireless client called victim (Step
1) is writing an e-mail to the friend (e-mail will go to the internet), asking
for money return of 1000$ and putting bank account number in the e-mail.
Assuming
the information is not well encrypted (or attacker broke the encryption and
have the chance of reading everything in clear text), wireless attacker (Step
2) reads the whole packet flowing in the air to the AP. The attacker modifies a
message by swapping the bank account number to its own and re-inject a message
back to the air, to go to the internet via the AP.
In
that situation, if there are no integrity checks that would detect a change in
the content of the message - the recipient would get a message with a modified
bank account number. Probably, the situation described would be extremely hard
to implement in real life, since all the tools like mail exchange, are secure
against those types of attacks (via proper encryption and message integrity
checks), it perfectly shows the concept of the attack.
There
are 2 main counter-measures against this type of an integrity attack −
encryption (so that attacker would not be able to read the message at all) and Message Integrity Codes(MICs) that are
basically hashing function like MD5 or SHA1that take a footprint of the whole
message and create a hash of 128 bits (MD5) or 160 bits (SHA1). Anytime, there
is a change in the packet content, the hash value would also change, resulting
in message being denied (already by wireless router).
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