CEH Practice Question: Advanced Topics: Wireless, Cloud, IoT, Cryptography
Which cryptographic algorithm is classified as symmetric and uses a block cipher with key sizes of 128, 192, or 256 bits?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
AES
AES is a symmetric block cipher that supports key sizes of 128, 192, and 256 bits, and is widely used for encryption.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
AES
Why this is correct
AES (Advanced Encryption Standard) is correctly classified as a symmetric block cipher, meaning it utilizes the same secret key for both encrypting and decrypting data. It processes data in fixed-size blocks and supports key lengths of 128, 192, or 256 bits, making it highly efficient for bulk data encryption. Its widespread adoption as a standard for secure communication underscores its robust symmetric properties.
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ECC
Why it's wrong here
Elliptic Curve Cryptography (ECC) is fundamentally an asymmetric cryptographic algorithm, relying on the mathematical properties of elliptic curves over finite fields for its security. Unlike symmetric algorithms, ECC employs a distinct public key for encryption and a corresponding private key for decryption, making it suitable for key exchange and digital signatures. Its asymmetric nature means it does not fit the criteria of a symmetric algorithm as specified in the question.
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Diffie-Hellman
Why it's wrong here
Diffie-Hellman is a renowned key exchange protocol, not an encryption algorithm itself, and therefore is neither symmetric nor asymmetric in the context of data encryption. Its primary function is to enable two parties to securely establish a shared secret key over an insecure communication channel. This shared secret can then be used by a symmetric encryption algorithm, like AES, for subsequent secure data transmission.
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RSA
Why it's wrong here
RSA (Rivest-Shamir-Adleman) is a prominent asymmetric cryptographic algorithm, distinguished by its use of a public-private key pair derived from the computational difficulty of factoring large prime numbers. The public key encrypts data, while only the corresponding private key can decrypt it, making it unsuitable for the 'symmetric' classification. It is widely employed for secure data transmission, digital signatures, and key exchange in public-key infrastructure.
Quick reference
Symmetric Encryption Algorithm Comparison
| Algorithm | Key Size | Block Size | Status | Notes |
|---|---|---|---|---|
| AES-128 | 128-bit | 128-bit | Current standard | NIST approved; WPA3, TLS |
| AES-256 | 256-bit | 128-bit | Current standard | Preferred for sensitive / govt data |
| 3DES | 112-bit effective | 64-bit | Deprecated (2023) | Replaced by AES |
| DES | 56-bit | 64-bit | Broken | Cracked in < 24 h; never deploy |
| ChaCha20 | 256-bit | Stream cipher | Current | TLS 1.3, WireGuard |
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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