Explanation/Reference:
Explanation:
The certificate used for the backup vault in Azure must fulfill the following prerequisites:
You can create a self-signed certificate using the makecert tool, or use any valid SSL certificate issued

by a Certification Authority (CA) trusted by Microsoft, whose root certificates are distributed via the Microsoft Root Certificate Program.
The certificate should be an x.509 v3 certificate.

The certificate must have a valid ClientAuthentication EKU.

To upload to the certificate to the vault, you must export it as a .cer format file that contains the public

key.
The key length should be at least 2048 bits.

The certificate should be currently valid with a validity period that does not exceed 3 years.

The certificate should reside in the Personal certificate store of your Local Computer.

The private key should be included during installation of the certificate.

References: https://blogs.technet.microsoft.com/hybridcloud/2014/03/16/using-azure-backup-with-dpm/