GSEC Cryptography Practice Question
A security engineer is implementing a digital signature solution using RSA. The engineer must ensure that signatures provide authenticity, integrity, and non-repudiation. Which TWO of the following practices are essential to achieve these goals? (Choose two.)
⚠ Common exam trap
It's easy for candidates to confuse digital signatures with encryption, leading to the misconception that the recipient's public key or the sender's private key is used to encrypt the whole message.
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
✓
Hash the message with a collision-resistant hash function before signing.
To create a digital signature with RSA, the sender must hash the message using a collision-resistant hash function and then sign that hash with their private key. This provides integrity (via the hash), authenticity and non-repudiation (via the private key signature). The recipient can verify by hashing the message and decrypting the signature with the sender's public key.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Hash the message with a collision-resistant hash function before signing.
Why this is correct
Signing a hash of the message rather than the raw message is essential for performance and security. A collision-resistant hash ensures that it is infeasible to find two different messages with the same hash, which would allow signature forgery. This practice is fundamental to achieving integrity and non-repudiation in digital signatures.
- ✗
Include a timestamp from a trusted Time Stamping Authority (TSA) in the signature.
Why it's wrong here
A timestamp from a TSA proves that the signature existed at a certain time, which is useful for long-term validation and non-repudiation in some contexts. However, it is not essential for basic digital signature authenticity and integrity. The core requirements are hashing and using the signer's private key. Timestamps are an additional layer, not a fundamental practice.
- ✗
Use the recipient's public key to encrypt the hash before signing.
Why it's wrong here
Digital signatures use the signer's private key, not the recipient's public key. Encrypting the hash with the recipient's public key would provide confidentiality to the recipient but not a signature. Signatures must be verifiable by anyone with the signer's public key, so this practice is incorrect and does not achieve authenticity or non-repudiation.
- ✗
Encrypt the entire message with the sender's private key.
Why it's wrong here
Encrypting the entire message with the sender's private key is not a standard digital signature practice. It would be computationally expensive and does not provide confidentiality, since anyone with the public key could decrypt it. Moreover, signing is not encryption; it is a separate cryptographic operation. This approach is inefficient and incorrect for achieving the stated goals.
- ✓
Sign the hash with the sender's private key.
Why this is correct
Signing the hash with the sender's private key is the core operation of a digital signature. Only the sender possesses the private key, so a valid signature verifies that the sender originated the message. This provides authenticity and non-repudiation because the sender cannot deny having signed the message, assuming the private key is securely held.
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 |
About these practice questions
This GSEC question is part of Courseiva's 351-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official GIAC exam blueprint
This GSEC practice question is part of Courseiva's free GIAC 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 GSEC exam.