Question 347 of 1,013
Digital Signature: Proving Authenticity and Integrity
Exhibit
Package verification steps: 1. sha256sum update.zip = 9f7c2a4b6f1d8e4c... 2. Vendor website shows the same hash 3. openssl dgst -sha256 -verify vendor_pub.pem -signature update.zip.sig update.zip Verified OK Audit note: The security team wants proof of origin, not just proof that the file content stayed the same.
Based on the exhibit, which cryptographic mechanism provides proof that the update came from the vendor and was not altered?
Quick Answer
The answer is digital signature, because only the vendor’s private key can produce a signature that verifies with the corresponding public key, proving both authenticity and integrity. A digital signature uses asymmetric cryptography: the vendor signs the update with their private key, and the customer validates it using the vendor’s public key. If the signature checks out, the update is confirmed as coming from the vendor and unaltered, since any tampering would break the cryptographic verification. On the Security+ SY0-701 exam, this concept tests your understanding of how digital signatures differ from hashing—hashing alone ensures integrity but not authenticity, as it lacks a private key component. A common trap is confusing a hash value for a signature; remember that a hash only detects changes, while a digital signature also proves the source. Memory tip: “Sign with private, verify with public—hash is just a fingerprint, a signature is a sealed envelope.”
⚠ Common exam trap
Many candidates confuse hashing with digital signatures, thinking that a hash match alone proves the source, when in fact hashing only verifies integrity, not authenticity or non-repudiation.
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
✓
Digital signature, because only the vendor's private key can produce the verified signature.
A digital signature uses the vendor's private key to sign the update, and the customer verifies it using the vendor's public key. This asymmetric cryptographic mechanism ensures both authenticity (the update came from the vendor) and integrity (the update was not altered), as only the vendor's private key can produce a signature that validates with the corresponding 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.
- ✗
Hashing, because matching SHA-256 values alone prove the file came from the vendor.
Why it's wrong here
A hash can confirm integrity if the expected value is trustworthy, but it does not prove who created the file or the hash. If an attacker can alter both the file and the published hash source, the match becomes meaningless. The exhibit asks for proof of origin, which requires more than a checksum comparison.
- ✗
Symmetric encryption, because only the vendor and the customer share the secret key.
Why it's wrong here
Symmetric encryption protects confidentiality, but it does not provide a strong public proof of origin for software distribution. Both sides would need the same secret key, and sharing that key widely would make distribution and verification harder. The scenario is about authenticity and tamper evidence, which are better addressed by signatures.
- ✓
Digital signature, because only the vendor's private key can produce the verified signature.
Why this is correct
Digital signature is correct because the signature check proves both integrity and authenticity. The vendor signs the update with a private key, and anyone with the matching public key can verify that the file has not changed and that the signer possessed the private key. That is exactly the proof of origin the audit note is asking for.
- ✗
Salting, because adding random data makes the update file easier to trust.
Why it's wrong here
Salting is used with password hashing to make precomputed attacks harder. It is not a mechanism for proving software origin or file integrity. Adding a salt would not tell the customer who created the update or whether it was altered after signing. The concept belongs to password storage, not software verification.
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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Same concept, more angles
1 more way this is tested on SY0-701
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Before installing a vendor patch package on hundreds of endpoints, the security team wants to confirm the file was published by the vendor and was not altered during download. Which two verification steps should the team perform? Select two.
hard- ✓ A.Verify the package signature with the vendor's public key.
- ✓ B.Compare the downloaded package hash to the hash in the signed manifest.
- C.Decrypt the package with the vendor's private key before installation.
- D.Rotate the organization's internal encryption key before downloading.
- E.Check only the file timestamp and size on disk.
Why A: Verifying the package signature with the vendor's public key confirms the package was cryptographically signed by the vendor, proving its authenticity and integrity. This process uses asymmetric cryptography where the vendor signs the package with their private key, and the security team uses the corresponding public key to validate that signature. Additionally, comparing the downloaded package hash to the hash provided in the signed manifest ensures that the file content exactly matches what the vendor published, detecting any alteration during download. These two steps together provide strong assurance that the package is genuine and unchanged.
Last reviewed: Jun 11, 2026
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