Information Security · Unit 3
Symmetric Encryption
Exam-focused notes for Symmetric Encryption (Information Security, BIT303): what the TU syllabus asks and how it has actually been tested, with 4 solved past questions from this unit.
What this unit covers
- Symmetric cryptography principles
- DES algorithm and round operations
- DES sub-key generation
- S-box operations in DES
- DES encryption and decryption
- Hill cipher and matrix operations
DES encryption and decryption
Discuss how encryption and decryption is done in the DES algorithm.[10]
DES (Data Encryption Standard) is a symmetric-key block cipher developed by IBM and adopted as a federal standard by NIST in 1977. It encrypts data in 64-bit blocks using a 56-bit key and performs 16 rounds of substitution and permutation operations. --- Pa...
Full solved answer →S-box operations in DES
What is the use of S-box in DES? Illustrate S-box operation with an example. [5]
This is a conceptual/illustrative question. The only numeric data needed comes from the standard DES S-box specification (the S1 table) and a chosen example input. No numeric data is supplied in the question itself, so I use the standard DES S1 table and th...
Full solved answer →DES algorithm and round operations
What is symmetric cryptography? Explain round operation of DES algorithm. Describe Sub-Key generation process for DES rounds.[10]
Note: No curriculum notes were found for this topic. The answer below is based on standard, well-established cryptography curriculum content as taught in BSc CSIT programs. --- Symmetric cryptography (also called secret-key or conventional cryptography) is ...
Full solved answer →Hill cipher and matrix operations
Decrypt the cipher text "CRHG" using the Hill cipher with the key matrix $$\begin{bmatrix} 3 & 4 \ 3 & 5 \end{bmatrix}$$. [5]
- Ciphertext: CRHG - Key matrix: $K = \begin{bmatrix} 3 & 4 \\ 3 & 5 \end{bmatrix}$ - Alphabet mapping: A = 0, B = 1, ..., Z = 25 - Modulus: 26 C R H G ------------ 2 17 7 6 Column vectors: $\begin{bmatrix}2\\17\end{bmatrix}$, $\begin{bmatrix}7\\6\end{bmatr...
Full solved answer →Make Unit 3 stick
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