SSL and Code Signing are two very different uses for encryption. SSL is a protocol for securing communication in real-time. Code signing is a time-stamped signature that can be used to verify publisher identity and software integrity. Outside of the fact that both make use of public key encryption, there’s not much other overlap. Certificates are issued with their intended purpose coded and signed into the certificate itself, in the Extended Key Usage field. https://comodosslstore.com/resources/can-i-use-an-ssl-certificate-for-code-signing/

The most likely cause of the signature failing is that the certi fi cate is set for the wrong key usage. Key usage is anextension of a certi fi cate that defi nes the purpose and functi onality of the public key contained in the certi fi cate.Key usage can include digital signature, key encipherment, data encipherment, certi fi cate signing, and others. Ifthe certi fi cate is set for a diff erent key usage than digital signature, it will not be able to sign the applicati onsproperly. The administrator should check the key usage extension of the certi fi cate and make sure it matches the intended purpose.

Verify Key Pair Compatibility: Ensure that the key pair used for signing is compatible with the applications. Verify that the algorithms and key lengths match the requirements of the signing process for the applications

It's C

Timing is essential, but I think incorrect implementation is more common. Source: Verifying each answer against Chat GPT, my experience, other test banks, a written book, and weighing in the discussion from all users to create a 100% accurate guide for myself before I take the exam. (It isn't easy because of the time needed, but it is doing my diligence)

the MOST likely cause of the signature failing on all applications despite the key pair working properly on the website is option C: The certificate is set for the wrong key usage. Digital certificates are used to verify the identity of the signer and ensure the integrity of the signed content. Certificates have specific key usage flags that indicate what the certificate can be used for. For example, a certificate may be issued for digital signatures or for encryption. If the certificate is not set up for the correct key usage, it will not be able to sign the application correctly. Therefore, it is likely that the certificate being used to sign the applications has been set up for the wrong key usage, causing the signature process to fail. The administrator should review the certificate's key usage and ensure it is set up correctly for signing applications.

Having taught CA design and implementation, I've seen this NTP issue multiple times when students forget set the correct time in their VM labs. If the machine that cuts a CSR is not within the time threshold of the Signing CA, i.e. is in the future, this is a typical error. You can try it yourself by building it out on a VM=)

Agree with C

The most likely cause of the signature failing is that the certificate is set for the wrong key usage. Digital signatures typically require a certificate with the key usage of "digital signature" enabled. If the certificate is not set for this key usage, it will not be able to be used for signing applications. Other possible causes, such as issues with the NTP server or the CA's CRL, would not affect the ability of the certificate to be used for signing. Similarly, missing a SAN or wildcard entry on the certificate would not cause the signing process to fail.

A is the correct answer

What can I do for when my 'certificate is not yet valid'? configure NTP​​ The time is not configured properly https://learn.umh.app/guides/open-source/k3os/troubleshooting/fix-not-yet-valid-cert/