Questions & Answers on Symmetric Block Cipher and Encryption Process

1QUESTIONS & ANSWERS
QUESTIONS & ANSWERS
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2QUESTIONS & ANSWERS
SECTION A
Answer ALL questions.
Question 1(a)
The “mode of operation” concept in a symmetric block cipher is an algorithm that
utilizes block cipher in order to provide information services such as authenticity and
confidentiality. This is because block ciphers when independent are only suitable for securing
cryptographic transformations i.e1 decryption and encryption of fixed-length bits also known
as blocks. Mode of operation, therefore, describes how single-block ciphers are applied
repeatedly in operations to transform larger amounts of data securely. Most of the modes
require unique binary sequences, commonly known as the initialization vector (IV) for
different encryption operations.
Cipher-Block Chaining (CBC) Mode
CBC encryption mode which was invented in 1976 mainly entails the addition
of XOR in any plaintext block to ciphertext block produced. The resulting text is then
encrypted by a cipher algorithm as usual. For that matter, subsequent ciphertext blocks
depend on the previous ones. XOR is added to the initial plaintext block’s random
initialization vector which has the same size as the plaintext block.
Cipher-Block Chaining (CBC) advantages
 With this mode, equal messages utilizing similar keys are encrypted to different
cryptograms
 Messages encrypted in this mode can be decrypted from any part
1MJ Dworkin. Recommendation for block cipher modes of operation: The CMAC mode for authentication. 2016 Oct 6.

3QUESTIONS & ANSWERS
 Its error multiplication features strengthen its security
Cipher-Block Chaining (CBC) disadvantages
 The message length under this mode must be aligned with its cipher block size
 After modification of message blocks, they cannot be re-encrypted
 Implementation of decryption is needed
 In case an attacker succeeds in inserting some parts into the message and gets the
ciphertext; parts of user messages are compromised.
Question 1(b)
Based on the communication layer where the encryption process takes place, there are
three different types of encryption namely SSL, TLS and HTTPS2
SSL stands for Secure Sockets Layer, a type of encryption operating at the
presentation layer to secure internet connections and safeguard sensitive data being sent
between two systems to prevent it from being read or modified in the course of transmission.
TSL which stands for Transport Layer Security, on the other hand, is an updated and
more secure version of SSL operating under the transport layer and which has the three
options of encryption: RSA, ECC or DSA
HTTPS which stands for Hyper Text Transfer Protocol Secure and operates under the
application layer is a form of encryption which appears on the URL of a website which has
been secured using an SSL certificate.
2 P.A Grassi, EM Newton, RA Perlner, AR Regenscheid, WE Burr, JP Richer, NB Lefkovitz, JM Danker, YY Choong, K
Greene, MF Theofanos. Digital identity guidelines: Authentication and lifecycle management. 2017 Jun 22.

4QUESTIONS & ANSWERS
Among the three, SSL and TLS are likely to raise ethical considerations because they
entail the security of private information which according to privacy policies should be kept
confidential.
Question 1(c) (i)
Government agencies and lawyers will definitely be against the idea of people being
allowed to create encryptions that cannot be broken by the argument. First of all, they will
argue that the approach will put national security under risk because terrorists will be able to
communicate from different places and make terror attacks whose success rate will be high
due to lack of intelligence3.
Secondly, they will argue that the approach will deter criminal investigations
especially investigations regarding online transactions. In this matter, they will argue that
most of the offenders will upgrade into online platforms like PayPal and Shrill where
evidence won’t be easily obtainable considering the fact that their communication will be on
an encrypted format which cannot break.
Question 1(c) (ii)
The advocates of free software and human rights will support the idea because they
will look at it from the privacy protection point of view. They will argue that government
agencies and their lawyers are normal human beings like any other and being granted an
opportunity to have access to private information is a compromise to privacy of other people.
Question 1(c) (iii)
According to me, individuals should not be allowed to create encryptions which
cannot be broken by the government. This is in consideration of the dangers which the idea is
3 P Mell, K Scarfone, S Romanosky. A complete guide to the common vulnerability scoring system version 2.0 (2007).
Διαθέσιμο On-line στο: http://www. first. org/cvss/cvss-guide. pdf [Accessed 20 March 2012]. 2017.