SC-900 Practice Question: Describe the concepts of security, compliance, and identity
A company uses digital signatures on all official emails sent to customers. The signature is created using the sender’s private key, allowing recipients to verify that the email truly came from the claimed sender and that it was not altered in transit. Which security goal is primarily achieved by the digital signature?
⚠ Common exam trap
Candidates often confuse integrity with non-repudiation, but while digital signatures do ensure integrity, the primary security goal they achieve is non-repudiation because they provide cryptographic proof of the sender's identity that cannot be repudiated.
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
✓
Non-repudiation
Digital signatures use asymmetric cryptography where the sender signs the email with their private key. The recipient can verify the signature using the sender's public key, which proves the identity of the sender and ensures the message has not been tampered with. This directly achieves non-repudiation because the sender cannot deny having sent the email, as only their private key could have created the signature.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Confidentiality
Why it's wrong here
Confidentiality ensures that information is accessible only to authorized individuals, preventing unauthorized disclosure. Digital signatures, however, do not encrypt the content of an email; they only provide authentication of the sender and verification of message integrity. To achieve confidentiality, the email's content would need to be encrypted using the recipient's public key, ensuring that only the intended recipient possessing the corresponding private key can decrypt and read the message.
When this WOULD be correct
A question asking which security goal is achieved by encrypting the email body with the recipient's public key, or by using a symmetric key to encrypt data before transmission, would have confidentiality as the correct answer.
- ✗
Integrity
Why it's wrong here
While digital signatures are instrumental in verifying message integrity, ensuring that the email has not been altered in transit, this is not the primary benefit highlighted by the scenario's emphasis on "official emails sent to." Digital signatures work by signing a hash of the email content; if any part of the email changes, the recipient's re-calculated hash will not match the signed hash, indicating tampering. However, the core purpose of digitally signing "official emails" is typically to prevent the sender from later denying they sent it, which is the definition of non-repudiation.
When this WOULD be correct
A question that asks: 'Which security goal ensures that data has not been modified during transmission?' In that context, integrity is the correct answer, as it focuses solely on detecting unauthorized changes, not on sender identity or non-repudiation.
- ✗
Availability
Why it's wrong here
Digital signatures ensure non-repudiation and integrity by binding the sender’s identity to the email via asymmetric cryptography, whereas availability concerns uninterrupted access to systems and data—a requirement not addressed by signing an email. This option tempts because availability is a core security triad pillar, and a recipient might assume that a verifiable signature guarantees the email service remains accessible; however, availability would be the correct choice only if the scenario described a denial-of-service attack or redundant infrastructure ensuring the email system stays online.
When this WOULD be correct
In a scenario where a company implements redundant servers and failover mechanisms to ensure that its email system remains operational even during a hardware failure, the security goal primarily achieved is availability.
- ✓
Non-repudiation
Why this is correct
Digital signatures achieve non-repudiation by cryptographically linking a message to its sender in a way that cannot be legitimately denied later. When a sender signs an email with their unique private key, they are essentially creating an unforgeable proof of origin. This signature, verifiable by anyone using the sender's public key, confirms that only the holder of that specific private key could have sent the message, thereby preventing the sender from disavowing their actions.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The SC-900 exam frequently reuses these exact scenarios with slightly different constraints.
✓Non-repudiationCorrect answer▾
Why this is correct
Digital signatures achieve non-repudiation by cryptographically linking a message to its sender in a way that cannot be legitimately denied later. When a sender signs an email with their unique private key, they are essentially creating an unforgeable proof of origin. This signature, verifiable by anyone using the sender's public key, confirms that only the holder of that specific private key could have sent the message, thereby preventing the sender from disavowing their actions.
✗ConfidentialityWrong answer — click to see why▾
Why this is wrong here
Digital signatures do not encrypt the email content; they only provide authentication and integrity verification. Confidentiality is about preventing unauthorized access, which is not achieved by signing with a private key.
★ When this WOULD be the correct answer
A question asking which security goal is achieved by encrypting the email body with the recipient's public key, or by using a symmetric key to encrypt data before transmission, would have confidentiality as the correct answer.
Why candidates choose this
Candidates may confuse digital signatures with encryption because both involve cryptographic keys, or they might think that signing ensures the message is hidden from eavesdroppers.
✗IntegrityWrong answer — click to see why▾
Why this is wrong here
Digital signatures primarily ensure non-repudiation and integrity, but the question specifically asks for the goal 'primarily achieved.' While integrity is partially achieved (detecting tampering), the primary goal is non-repudiation—proving the sender's identity and preventing denial. Integrity alone does not tie the signature to a specific sender's private key.
★ When this WOULD be the correct answer
A question that asks: 'Which security goal ensures that data has not been modified during transmission?' In that context, integrity is the correct answer, as it focuses solely on detecting unauthorized changes, not on sender identity or non-repudiation.
Why candidates choose this
Candidates may confuse integrity with non-repudiation because digital signatures do verify that the message was not altered (integrity). They overlook that the signature's primary purpose is to bind the sender's identity to the message, which is non-repudiation.
✗AvailabilityWrong answer — click to see why▾
Why this is wrong here
Digital signatures primarily ensure non-repudiation and integrity, not availability. Availability refers to systems and data being accessible when needed, which is not addressed by digital signatures.
★ When this WOULD be the correct answer
In a scenario where a company implements redundant servers and failover mechanisms to ensure that its email system remains operational even during a hardware failure, the security goal primarily achieved is availability.
Why candidates choose this
Candidates may confuse integrity (which digital signatures also provide) with availability, or mistakenly think that signing ensures the email service is always up.
Analysis generated from the official SC-900blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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 |
Go deeper
Related to this question
Learn chapter
Core Security Concepts
Key term
Non-repudiation
Non-repudiation is a security principle that ensures a party in a digital transaction cannot deny their involvement or the authenticity of their digital signature.
Key term
Security
Security in IT is the practice of protecting systems, networks, and data from unauthorized access, damage, or theft.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SC-900 practice question is part of Courseiva's free Microsoft 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 SC-900 exam.