200-201 Security Concepts Practice Question
A security analyst needs to ensure that a message has not been tampered with during transit and that the sender cannot deny sending it. Which cryptographic method should be used?
⚠ Common exam trap
Cisco often tests the distinction between hashing (which provides integrity only) and digital signatures (which provide both integrity and non-repudiation), leading candidates to mistakenly choose hashing when non-repudiation is required.
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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Digital signature
A digital signature provides both integrity (ensuring the message has not been tampered with) and non-repudiation (preventing the sender from denying they sent it). It works by hashing the message and encrypting that hash with the sender's private key; the recipient verifies the signature using the sender's public key. This cryptographic method uniquely binds the sender to the message, unlike other options that only address one of these requirements.
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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Digital signature
Why this is correct
A digital signature uses the sender's private key to sign a message hash, letting the recipient verify integrity via the public key and providing non-repudiation, since only the sender could have produced that signature. This satisfies both the tamper-detection and non-deniability requirements.
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Symmetric encryption
Why it's wrong here
Symmetric encryption uses one shared secret key for confidentiality, providing neither tamper detection nor sender non-repudiation, since both parties hold the same key. It is the right choice for bulk data confidentiality, such as encrypting stored files or VPN tunnels, not for proving integrity and origin.
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Hashing
Why it's wrong here
Hashing alone detects alteration but uses no key, so anyone can recompute a digest; it cannot bind a message to a sender or prevent denial. Hashing is correct for verifying file integrity or storing password digests, not for authenticating origin.
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Public key infrastructure (PKI)
Why it's wrong here
PKI is the framework of certificates, CAs and revocation that issues and validates keys; it does not itself provide the message-level integrity and non-repudiation properties required. A digital signature, generated with the sender's private key and verified with their public key, delivers both. PKI would be the choice when deploying certificates at scale.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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