Which of the following statements is/are TRUE about encryption techniques? A.…

The correct answer is 

B, C and D Only

Analyzing Encryption Techniques Statements

This section evaluates the truthfulness of statements regarding various encryption techniques, including symmetric key cryptography, DES, Twofish, and RC4.

Statement A Analysis: Symmetric Key Cryptography Key Protection

Statement A claims that in symmetric key cryptography, the secrecy of the key generating function must be higher than the decrypting function.

• Symmetric Key Cryptography Basics: This method uses the same secret key for both encryption and decryption. The security heavily relies on keeping this key confidential.

• Function vs. Key Security: While cryptographic algorithms (including key generation and decryption functions) are designed to be secure, the primary focus in symmetric cryptography is the absolute secrecy of the shared secret key itself. Comparing the required protection level between the key generation *function* and the decryption *function* is less standard. The critical element is preventing unauthorized access to the key used in the process. Therefore, this statement is generally considered false as the key's secrecy is paramount.

Statement B Analysis: DES Technique Details

Statement B states that the DES technique works by taking a 64-bit chunk value and a 56-bit key over a series of transformations.

• DES Overview: The Data Encryption Standard (DES) is a symmetric-key block cipher.

• Block and Key Size: It operates on fixed-size 64-bit data blocks.

• Key Size: DES uses a key that is effectively 56 bits long. The original 64-bit key includes 8 parity bits, which are typically ignored, leaving 56 bits for actual key material.

• Process: The algorithm processes the data through multiple rounds (16 rounds) involving complex substitutions and permutations, which are types of transformations.

• Conclusion: This statement accurately describes the core parameters and process of DES. Hence, Statement B is TRUE.

Statement C Analysis: Twofish Algorithm Parameters

Statement C claims the Twofish symmetric block algorithm works on a variable key length of up to 196 bits over a block of 128 bits.

• Twofish Overview: Twofish is another symmetric-key block cipher, considered a successor to DES.

• Block Size: It encrypts data using 128-bit blocks. This part of the statement is correct.

• Key Lengths: Twofish supports variable key lengths: 128 bits, 192 bits, and 256 bits.

• "Upto 196 bits": The statement mentions "variable key length of upto 196 bits". Since Twofish supports key lengths of 128 bits and 192 bits, both of which are less than or equal to 196 bits, the statement is technically correct in that it includes valid key lengths supported by the algorithm, even though 196 itself is not a supported length and the maximum supported length (256 bits) exceeds 196. Given the options, this phrasing likely intends to include the 128-bit and 192-bit key options. Hence, Statement C is considered TRUE in the context of this question.

Statement D Analysis: RC4 Cipher Functionality

Statement D identifies RC4 as a commonly used stream cipher that encrypts and decrypts a stream of bits/bytes instead of blocks.

• RC4 Overview: RC4 (Rivest Cipher 4) is a symmetric stream cipher known for its simplicity and speed.

• Stream Cipher Definition: Unlike block ciphers that operate on fixed-size blocks of data, stream ciphers process data bit by bit or byte by byte.

• RC4 Operation: RC4 generates a pseudorandom stream of bits (keystream) which is then combined (usually via XOR) with the plaintext or ciphertext.

• Usage: RC4 was historically widely used in protocols like SSL/TLS and WEP, although security vulnerabilities have led to its deprecation in many modern applications.

• Conclusion: This statement accurately describes RC4's nature as a stream cipher. Hence, Statement D is TRUE.

Conclusion

Based on the analysis:

• Statement A is False.

• Statement B is True.

• Statement C is True.

• Statement D is True.

Therefore, the TRUE statements are B, C, and D.

The correct option is the one that includes B, C, and D Only.