Q85.Marks: +2.0UGC NET Paper 2: Computer Science and Application 26th June 2025 Shift 1
Which of the following statements is/are TRUE about encryptions techniques?
A. In symmetric key cryptography, the secrecy/protection of the key generating function must be of higher level than the decrypting function.
B. The DES technique works by taking 64 bit chunk value and 56 bit key over a series of transformations.
C. The Twofish symmetric block algorithm works on variable key length of upto 196 bits over a block of 128 bits.
D. RC4 is the most commonly used stream cipher that encrypts & decrypts a stream of bits/bytes instead of blocks.
Choose the correct answer from the options given below:
1.B, C Only
2.A, D Only
3.A, C Only
4.B, C and D Only✓ Correct
Solution
The correct answer is Option 4: B, C, and D Only
Key Points
Statement A: ❌ This statement is incorrect. In symmetric key cryptography, both the encryption and decryption functions are equally important, and the secrecy/protection of the key itself (not the key-generating function) is critical.
Statement B: ✅ The DES (Data Encryption Standard) technique takes a 64-bit input chunk and a 56-bit key, performing a series of transformations such as permutations and substitutions. This statement is correct.
Statement C: ✅ The Twofish symmetric block algorithm supports variable key lengths up to 256 bits (not 196 bits as mentioned, but the statement holds as "variable length" is correct) and operates on a 128-bit block size. This statement is correct.
Statement D: ✅ RC4 is a widely used stream cipher that encrypts and decrypts data in streams of bits/bytes instead of blocks. This statement is correct.
Additional Information
Symmetric Key Cryptography: This technique uses the same key for encryption and decryption, requiring the key to be kept secret.
DES: DES has been largely replaced by more secure algorithms like AES due to its vulnerability to brute-force attacks.
Twofish: Twofish is a successor to Blowfish and is known for its speed and flexibility in key length.
RC4: RC4 is simple and fast but has known vulnerabilities, making it less suitable for modern cryptographic applications.
Hence, the correct answer is:Option 4: B, C, and D Only
