Claude Shannon presented the encryption design principles of-1

Assignment Brief

INFA 640 Homework 2
Choose the best answer (one) and give reason in a few sentences for your choice or not choosing others. Please give a reference. To get full credit the reason should be in your own words, not a copy from any reference. Without reason in your own words you will not get full credit.

Claude Shannon presented the encryption design principles of _________________.

1. multiplication and factoring
2. exponentiation and Logarithms
3. confusion and diffusion
4. perplexion and reflection

Reason: how and why those principles guide the encryption?

A good hash function creates _________ mapping between the source string and the output string.

1. complex
2. as many as needed
3. divisional
4. one to one

Reason why is it considered good?

To create a digital signature, a sender needs the plain text, the asymmetrical encryption algorithm, and ___________.

1. his/her public key
2. the receiver’s public key
3. his/her private key
4. the receiver’s private key

Reason How is it used?

A number is relatively prime to another if they _____________.

1. have only each other as factors
2. have no prime factors in common
3. only have one prime factor in common
4. are both divisible by 7

Reason:  

Repudiation means

Faking one’s identity

Uproot

Deny ownership

Plant clues in the text

Reason: Why it is important?

(25 pts) The following is a ciphertext:

ZQ GDH LMJ XHBIG JODHAC PD CLUJ XZUJF ZO KLMZV LV L GDHOA RLO, PCJO ECJMJUJM GDH AD QDM PCJ MJVP DQ GDHM XZQJ ZP VPLGV EZPC GDH, QDM KLMZV ZV L RDUJLNXJ QJLVP

JMOJVP CJRZOAELG

What kind of cipher text is this? Mono- or Poly alphabetic; [Hint: assume one and when that does not work look for the other] [2 points]

Describe your cryptanalysis process. List all the steps you went through to decrypt the message. The steps should be in sufficient details so that a reader would be able to decrypt the encrypted text without needing any help from you.

[If you find solution online or use online tools please give reference. However, you should describe the steps as if you are working without the tool, (Hint consider starting with the frequency analysis) to get full credit]

[If you list partial steps you will get partial credit]

[15points]

State the plain text message in readable form i.e. separating words if required

[the solution worked without the help from online tools will be given full credit] [2 pts]

List features of the cipher- text that hindered and helped your decryption process. mention of helpful and hindering features [ 6 pts]

Note: Only a decrypted message even if it is correct one without the methodology and the detailed description of the self-explanatory steps used to decrypt, would not get points.

Sample Answer

1. Claude Shannon presented the encryption design principles of: Answer:

Confusion and diffusion

Reason: Claude Shannon introduced these principles to enhance encryption security. Confusion means making the relationship between the key and ciphertext as complex as possible, so patterns are hidden. Diffusion means spreading the plaintext`s influence over the ciphertext to make statistical analysis ineffective. The other options, multiplication/factoring, exponentiation/logarithms, are mathematical operations, not encryption design principles.

Reference: Shannon, C. E. (1949). Communication Theory of Secrecy Systems.

2. A good hash function creates: Answer:

One to one

Reason: A strong hash function should ideally map each unique input to a unique output, meaning a one-to-one relationship. While hash collisions are theoretically possible due to limited output space, a good hash function minimises them. This ensures data integrity and supports authentication and digital signatures.

Reference: Stallings, W. (2017). Cryptography and Network Security.

3. To create a digital signature, a sender needs the plain text, the asymmetrical encryption algorithm, and: Answer

His/her private key

Reason: Digital signatures are created by encrypting a message digest with the sender`s private key. This ensures that only the sender could have signed it, providing authenticity. The receiver verifies the signature using the sender’s public key.

Reference: Katz, J., & Lindell, Y. (2014). Introduction to Modern Cryptography.

4. A number is relatively prime to another if they: Answer:

Have no prime factors in common

Reason: Two numbers are relatively prime (coprime) if their greatest common divisor is 1, meaning they do not share any common prime factor. This property is key in algorithms like RSA, where choosing coprime numbers ensures the algorithm works correctly.

Reference: Rosen, K. H. (2012). Discrete Mathematics and Its Applications.

5. Repudiation means: Answer:

Deny ownership

Reason: Repudiation refers to the act of a user denying that they sent a message or performed an action. In cybersecurity, it’s important to prevent this using digital signatures or logging, so that individuals cannot deny their actions.

Reference: Pfleeger, C. P., & Pfleeger, S. L. (2015). Security in Computing.

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