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SSCP Practice Question: In RSA, the public exponent e is often chosen as…
In RSA, the public exponent e is often chosen as 65537. What is the primary reason for this choice?
⚠ Common exam trap
ISC2 often tests the misconception that a larger exponent always means higher security, when in fact the exponent's size has negligible impact on security compared to the modulus length, and the real benefit of 65537 is performance due to its low Hamming weight.
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
✓
It offers a balance between security and performance due to low Hamming weight
65537 (0x10001) has a low Hamming weight of only 2 bits set, which makes modular exponentiation significantly faster than using a random large exponent, while still providing strong security. This choice balances computational efficiency with cryptographic strength, as a larger exponent would slow down encryption without proportional security gains.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
It ensures that the private key d is small
Why it's wrong here
e does not influence d size; d is computed from e and φ(n).
- ✗
It prevents side-channel attacks
Why it's wrong here
Side-channel attacks are mitigated by constant-time algorithms, not exponent choice.
- ✗
It provides the highest security level
Why it's wrong here
Security depends on key size, not exponent value within reason.
- ✓
It offers a balance between security and performance due to low Hamming weight
Why this is correct
Few 1 bits speed up modular exponentiation.
Quick reference
Asymmetric Encryption Algorithm Comparison
| Algorithm | Key Exchange | Signatures | Equivalent Security Key | Notes |
|---|---|---|---|---|
| RSA-3072 | Yes | Yes | 128-bit | Widely deployed; slow for bulk data |
| ECDSA P-256 | No | Yes | 128-bit | Fast signatures; standard TLS certs |
| ECDH / ECDHE | Yes | No | 128-bit | Perfect forward secrecy in TLS 1.3 |
| DH / DHE | Yes | No | 128-bit (3072-bit key) | Replaced by ECDHE in modern TLS |
| Ed25519 | No | Yes | ~128-bit | SSH keys, modern PKI |
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.