SSCP Cryptography Practice Question
An organization is implementing a digital signature solution to ensure non-repudiation of documents. Which combination of keys is used during the signing process?
⚠ Common exam trap
ISC2 SSCP often tests the misconception that signing uses a public key or that verification uses a private key, leading candidates to confuse the roles of keys in encryption versus signing.
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
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Sender's private key to sign, sender's public key to verify
Digital signatures use asymmetric cryptography where the sender creates a signature with their private key, and the recipient verifies it with the sender's public key. This ensures non-repudiation because only the sender possesses their private key, so they cannot deny having signed the document. The process typically involves hashing the document and encrypting the hash with the sender's private 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.
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Recipient's public key to sign, recipient's private key to verify
Why it's wrong here
The recipient's key pair is irrelevant to signing; only the sender's private key can produce a signature verifiable with the sender's public key. Using the recipient's keys would let the recipient forge signatures, destroying non-repudiation. This option confuses encryption to a recipient with signing by an originator.
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Sender's private key to sign, sender's public key to verify
Why this is correct
Non-repudiation requires the signer to use their private key, which only they hold, and verifiers to use the corresponding public key. This asymmetric pairing proves origin and prevents the sender denying authorship of the signed document.
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Sender's public key to sign, recipient's private key to verify
Why it's wrong here
Signing uses the sender's private key, not their public key, and verification uses the sender's public key, not the recipient's private key. The recipient's key pair plays no part in signing. This reversed pairing is tempting because public-key operations do involve both key types, but the signer must hold the private half.
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A shared symmetric key for both signing and verification
Why it's wrong here
Symmetric keys cannot provide non-repudiation: both parties hold the same secret, so either could have produced the signature. Symmetric cryptography suits bulk data confidentiality, such as AES session encryption, but digital signatures require the sender's private key to sign and the sender's public key to verify.
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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JA
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.