SY0-701 Question 43
Single answerDigital signaturesA software company distributes internal update packages to thousands of managed laptops. After a recent phishing incident, the security team wants to ensure administrators can verify that each package truly came from the build server and was not modified in transit. The team does not need to hide the package contents because the updates are not confidential. Which solution best meets this requirement?
- A
Digitally sign each update package with the build server's private key and have clients verify it with the corresponding public key
- B
Encrypt each update package with the build server's private key so only authorized laptops can decrypt it
- C
Hash each update package with SHA-256 and publish the hash on the company intranet without using any keys or certificates
- D
Compress each update package and store it on a restricted file share that only administrators can access
Show answer and explanation
Correct answer: A
Explanation
The best answer is to digitally sign the update package. In real software distribution, digital signatures are commonly used to validate publisher identity and verify package integrity. This matches security best practices and common PKI usage: the signer uses a private key to create the signature, and recipients validate it using the corresponding public key contained in a trusted certificate. Digital signatures provide integrity and authentication, while encryption provides confidentiality. A standalone cryptographic hash such as SHA-256 is useful for change detection but does not establish trust in the publisher unless the hash itself is authenticated. This aligns with standard guidance from NIST on digital signatures and integrity protections, including FIPS 186 for digital signature standards and broader PKI best practices described by NIST.
- A. Correct.
Correct. A digital signature provides integrity, authentication of the signer, and non-repudiation. The build server signs the package using its private key, and clients verify the signature using the associated public key, typically distributed through a certificate. If the package is altered after signing, signature verification fails. This directly addresses the requirement to prove origin and detect tampering without providing confidentiality.
- B. Incorrect.
Incorrect. Private keys are not used this way for confidentiality. In public key cryptography, data encrypted with a private key is not a standard method for restricting access because anyone with the public key could recover it. This option confuses digital signatures with encryption. Signatures use the private key to sign a hash of the data, not to encrypt the package for secrecy.
- C. Incorrect.
Incorrect. A plain SHA-256 hash can detect accidental or malicious changes only if the recipient already trusts the source of the hash. If an attacker can replace the package, they may also replace the published hash. Without a digital signature, HMAC, or another trusted authentication mechanism, the hash alone does not verify who created the package.
- D. Incorrect.
Incorrect. Compression and file share permissions do not provide cryptographic proof of origin or integrity after distribution. Access controls may reduce who can retrieve the file, but they do not allow every managed laptop to verify that the package was created by the authorized build server and not modified in transit or on a mirror.