Let's move on that the security measures for ensuring data confidentiality as we've said the first security
measure developed was what or what key is indirectly used not only for secure data but also to authenticate
computers one access point doesn't encrypt frames it can't decrypt if the frames were encrypted with
an incorrect Webcke it will be rejected.
What are the flaws of the web technology.
One of the fundamental rules of cryptography is that one should not be used frequently.
The more often you use the same key the less secure it becomes
the standard doesn't define any solutions for automating key generation.
If you wanted to change a key you'd have to do this manually and separately for each computer as a result
of this.
These are rarely changed
the encryption used in the standard is weak.
The process can be seen in the picture below.
It's necessary to calculate the checks some of the packet first.
It's an ordinary CRC checksum not a cryptographic hash function.
This means that the well protected packets are vulnerable to tamper and attacker can modify the contents
of the frame and forward it by calculating the correct checksum.
Checksum is hazarded Tuason packet we've mentioned already that this is not secured in any way.
RC for a stream cypher is used for encryption.
We'll talk about this cipher at the end of all modules in secure use of the RC for algorithm is based
on the rule that the key shouldn't be used more than once to encrypt the same data.
If this rule is flouted working the ciphertext is trivially easy.
Or C 4 is based on X or operations.
Let's leave aside cryptographic details for a moment.
The same data is exchanged repeatedly over the network this transmission doesn't relate to people visiting
the same web site.
It's about packet headers having a set structure
predicting field values of the headers is very easy.
Given those randomisation was required to improve security in this case randomisation is provided by
the presence of an initialization vector.
Ivy unfortunately it's just 24 bit 24 bit.
ITV is too small this doesn't end the list of problems though.
We'll return to that soon.
When an I.V. is used data stream has to be mapped to the keystream the exclusive or ex-SO are is used
for this purpose.
The end result is the ciphertext or the encrypted version of a packet that was sent to an access point
length depends on what version it can be a 64 bit or even 256 bit long even if the key is really long
you can ensure the security of a network on its own.
This is due to a small number of initialization vectors.
There's only 16 million seven hundred and seventy seven thousand two hundred sixteen available IVI values
in the pool.
The problem is that the risk of repeated values the risk of collision is much higher than it would seem
at first glance.
It's enough to capture more or less 5000 packets for the risk of finding two packets encrypted with
the same IP to be over 50 percent.
And having the same vector equals having the same key because as we said WEP doesn't support dynamic
change.
This means that we've managed to capture data encrypted with the same key.
All it takes now to extract nearly full information on the key is to combine the ciphertext using ex-SO
or
implementation of this week security mechanism is even worse.
The standard doesn't specify the entities responsible for generating Ivey's this has to be done by a
network card how standard doesn't say initially network card manufacturers use the following system.
One was for the Wii for encrypting the first packet two was for encrypting the second packet three for
the third it was highly predictable.
This means that there can be attacks that consist of assuming a specific value of a vector.
You can also encrypt data but not encrypt headers.
In that case an attacker is not only able to capture physical addresses of the clan he's eavesdropping
on.
You can also modify them.
You can control the packets transmitted in this network.
We've talked about the potential problems connected to adding up checksum to packets this issue will
be noticed for example by korek another's.
If we had a checksum to an encrypted packet there's a one to one relationship between the checks some
bits and the ciphertext
by modifying any checksum bit can determine the validity of any part of the packet.
The checksums will or won't match accordingly.
An access point rejects the packets that have an incorrect checksum.
This is a basic mechanism for maintaining reliability of data sent over wireless networks where there's
a lot of interference.
You can modify a ciphertext byte by byte modify the checksum and see if an access point rejects the
packet.
This will help you make sure whether or not you have correctly cracked the valid combination for the
key for each part.
The RC for algorithm is vulnerable to revealing certain relationships between the key NIV.
How can all of these problems be solved.
Don't use WEP to start with look at the alternative solutions.