Question

Consider the following statements about symmetric encryption :
A. Same key for encryption and decryption

B. Faster than asymmetric encryption

C. Key distribution is simpler

D. Stream ciphers encrypt one bit byte at a time

E. Block ciphers operate on groups of bits

Choose the correct answer from the options given below :

• A. A, B, C, E only
• B. B, C, D only
• C. A, C, D, E only
• D. A, B, D, E only

Hint:

Symmetric = Shared Key. Asymmetric = Public/Private pair. If you see "Simple Key Distribution," it's referring to Asymmetric/Public-key cryptography!

Answer 1

The Correct Option is D

Concept:
• Symmetric Encryption: A cryptographic system that uses a single shared secret key for both the encryption of plaintext and the decryption of ciphertext.
• Common types include DES, AES (block ciphers), and RC4 (stream ciphers).

Step 1: Evaluate the fundamental characteristics (A and B)
Symmetric encryption is defined by using a single shared key. Because the mathematical operations involved (like XOR and substitution) are less complex than the modular exponentiation used in Asymmetric systems (like RSA), symmetric encryption is significantly faster. Statements A and B are Correct.

Step 2: Evaluate the Key Distribution problem (C)
One of the major disadvantages of symmetric encryption is that the secret key must be shared securely between parties. As the number of users \(n\) grows, the number of keys required grows as \(O(n^2)\). This is much more complex than asymmetric systems. Statement C is Incorrect.

Step 3: Evaluate Ciphers types (D and E)
Stream ciphers convert plaintext to ciphertext by processing one bit or byte at a time using a keystream. Block ciphers divide the plaintext into fixed-size blocks (e.g., 64 or 128 bits) and process them as a single unit. Statements D and E are Correct.

Step 4: Conclusion
The correct set of statements is A, B, D, and E.