CISSP Security Architecture and Engineering Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  RC4

  Why this is correct

  RC4 is indeed a symmetric stream cipher, meaning it encrypts data one byte or bit at a time, generating a pseudorandom keystream that is then XORed with the plaintext to produce ciphertext. This approach makes it highly efficient for real-time communication and variable-length data streams, as it does not require padding to fixed block sizes. While widely used in protocols like WEP and SSL/TLS in the past, RC4 is now largely deprecated due to identified vulnerabilities when used improperly, particularly related to weak keys and non-random keystream generation.

• ✗

  AES

  Why it's wrong here

  AES (Advanced Encryption Standard) is a prominent example of a symmetric block cipher, not a stream cipher. It operates by encrypting fixed-size blocks of plaintext, typically 128 bits, using a secret key. Unlike stream ciphers that process data bit by bit, AES applies a series of substitutions, permutations, and other transformations to an entire data block simultaneously. Its security and efficiency have made it the global standard for symmetric encryption, widely implemented in various applications and protocols.

• ✗

  3DES

  Why it's wrong here

  3DES (Triple DES) is a symmetric block cipher that applies the original Data Encryption Standard (DES) algorithm three times to each data block. It processes data in 64-bit blocks, using either two or three distinct keys to enhance security beyond single DES, which was found vulnerable to brute-force attacks. Despite its improved security over DES, 3DES is considerably slower than modern block ciphers like AES and is gradually being phased out due to its smaller block size and computational overhead, though it still sees use in legacy systems.

• ✗

  RSA

  Why it's wrong here

  RSA is an asymmetric cryptographic algorithm, fundamentally different from symmetric ciphers like RC4, AES, or 3DES. Asymmetric cryptography, also known as public-key cryptography, utilizes a pair of mathematically linked keys: a public key for encryption and a private key for decryption. This distinct key pair allows for secure communication without prior sharing of a secret key, enabling digital signatures and key exchange, which symmetric algorithms cannot inherently provide.

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