Expert answer:paraphrase the answers.
Expert answer:Can you please paraphrase the answers of the attachment files. In which it does not change the meaning and write it in different way. ( you need to understand the answer well in order to do so.Thank you.
20171124084504security_doc__1_.docx
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1-Can you “decrypt” a hash of a massage to get the original message? Explain your answer.
No, it is not possible. A hash can’t be reversed means in no way can it be decrypted. The reason
for this being that hash functions are usually one-way functions. For instance, provided any kind
of hash value, the initial message can’t be recovered, e.g., provided with h in such a way that h =
H(m), m cannot in any way be recovered h).
“Decryption” to obtain the initial message can’t be possible as a result of the fixed length of the
hash and thus can be very short to be in possession of all the message contents at once. By design
a hash algorithm typically does not possess an inverse meaning there is not possible to obtain the
original message from the hash. This type of function is utilized in many applications where
messages validated and passwords stored securely meaning any tampering with file or message
can be easily determined.
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2- Suppose Alice has a message that she is ready to send to anyone who asks. Thousands of
people want to obtain Alice’s message, but each wants to be sure of the integrity of the
message. In this context, do you think a mac-based or a digital-signature-based integrity
scheme is more suitable? Why?
In this instance, people in thousands need to receive a message from Alice. They, however, want
assurance of message’s integrity. In this kind of circumstance, using digital-signature-based
integrity scheme is most appropriate here as compared to Message Authentication Code (MAC)
algorithm.
For Message Authentication Code based integrity schemes, shared keys for each receiver must be
maintained by Alice. For digital-signature-based integrity scheme, however, Alice can utilize
similar digital signatures for all receivers. MAC scheme has the advantage of not involving
complex encryption/decryption and involves reduced time however the message integrity is very
low which is the main objective of the people in thousands who desire to get the message from
Alice. Digital-signature-based integrity makes sure of increased message integrity being that they
are non-forgeable and verifiable.
If Alice utilizes the digital-signature-based integrity scheme, then she will make use of identical
digital signature for every receiver. If MAC algorithm kind of scheme is utilized, Alice will find
its management difficult as she has to maintain a single key that is shared for every receiver
involved. Deriving from this, digital-signature-based integrity scheme is the best option compared
to MAC algorithm scheme in this particular scenario.
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3-Suppose Bob initiates a TCP connection to Trudy who is pretending to be Alice. During
the handshake, Trudy sends Bob Alice’s certificate. In what step of the SSL handshake
algorithm will Bob discover that he is not communicating with Alice?
Step 1 of this process begins with Bob initiating a TCP connection with Trudy who sends Alice’s
certificate, in step 2. In step3, Bob verifies the certificate and identifies that the certificate belongs
to Alice and then goes ahead to extract Alice’s public key. Now, Bob produces a Pre-Master secret
(PMS) and encrypts it with the public key belonging to Alice, and transmits it to Alice (who in this
case is Trudy pretending to be Alice).
In step 4, both the sender and receiver have to create Master secret (MS) form nonces and PMS.
MS is split to produce two encryption keys as well as two MAC keys independently. Bob can
successfully create these four keys. But, Trudy can’t create Master secret (MS) and four keys,
since Trudy doesn’t know the private key of Alice, and can’t decrypt the PMS. So, Trudy guesses
random or false MAC keys. In the step5, bob sends the MAC of messages.
In step 6, Trudy sends MAC of messages. But these messages fail the MAC test. Thus, Bob finds
out he is not in communication with Alice. The moment Bob gets the MAC, the MAC test fails,
and the TCP connection is ended. Therefore, Bob can know he is not in communication with Alice,
in the final step (step 6) of SSL hand shake algorithm.
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4- Stateful packet filters maintain two data structures. Name them and briefly describe what
they do.
State full packet filters use the following two data structures:
1. Connection table
2. Access control list
State full packet filters the packets based on the information stored in the connection table
and access control list. That is, state full packet filter makes a decision whether the packet is
allowed or not, based on these tables’ information.
1. Connection Table
In the Stateful filters, the connection table is utilized in tracing information related to the current
TCP connection. The creation of entries in the tables takes place when a new TCP connection is
observed that is the moment SYN, SYNACK, and ACK are observed. An entry is gotten rid of,
the moment FIN bit is observed, an indication of the end of TCP connection.
2. Access control list
The access control list in the Stateful filter has a vital role in permitting and disallowing packets
via the firewall. The firewall plays an essential role in the access control list of maintaining filtering
rules. With this list as its basis, firewall makes decisions of allowing or disallowing packets. The
moment a packet arrives; the firewall first makes a check of the access control list. If access control
list shows that connection table must be checked, the firewall makes a check of this table and lastly
makes a decision on whether the packet is permitted or disallowed the connection.
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References
Dally, W. J., & Towles, B. P. (2004). Principles and practices of interconnection networks.
Elsevier.
Kurose, J. F., & Ross, K. W. (2012). Computer networking: a top-down approach
…
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