SSCP Cryptography Practice Question
A security analyst is reviewing a proposed solution that uses a stream cipher to encrypt real-time voice traffic. Which property of stream ciphers makes them well suited for this scenario?
⚠ Common exam trap
The trap here is attributing asymmetric or compression features to stream ciphers, or overlooking that their main advantage for voice is low latency and no padding.
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
✓
They encrypt data one bit or byte at a time, avoiding the need to pad to a block boundary.
Stream ciphers operate on small units of data, such as bits or bytes, and do not require padding to a block boundary. This makes them efficient for continuous, low-latency traffic like real-time voice, where waiting for a full block would add delay. They are symmetric and provide confidentiality only, so properties such as non-repudiation, per-call key pairs, and compression are not inherent to them.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
They require a unique public/private key pair for every call.
Why it's wrong here
Stream ciphers are symmetric and use a shared secret key, not public/private key pairs. Requiring a key pair per call would be an asymmetric design and would add significant overhead. This property is unrelated to the efficiency advantages that make stream ciphers attractive for voice traffic.
- ✓
They encrypt data one bit or byte at a time, avoiding the need to pad to a block boundary.
Why this is correct
Stream ciphers generate a keystream and combine it with plaintext one unit at a time, so they do not require padding and can handle continuous data streams. This is advantageous for real-time voice, where traffic is generated continuously and buffering to fill a block could introduce latency. The absence of padding also avoids ciphertext expansion.
- ✗
They provide built-in non-repudiation for each voice packet.
Why it's wrong here
Non-repudiation requires asymmetric digital signatures or comparable mechanisms; stream ciphers are symmetric and cannot provide it. A stream cipher only transforms plaintext into ciphertext using a shared secret. The scenario asks about suitability for real-time encryption, not about proving the origin of each packet.
- ✗
They automatically compress voice data before encryption.
Why it's wrong here
Stream ciphers do not perform compression; compression is a separate function that must be applied before encryption if desired. Combining compression and encryption incorrectly can also leak information. The advantage of stream ciphers in this context is their low latency and lack of padding, not any built-in compression capability.
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 and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official ISC2 exam blueprint
This SSCP practice question is part of Courseiva's free ISC2 certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SSCP exam.