If your environment uses vSphere Virtual Machine Encryption, and if an error occurs on the ESXi host, the resulting core dump is encrypted to protect customer data. Core dumps that are included in the vm-support package are also encrypted.
Core Dumps on ESXi Hosts
When an ESXi host crashes, and encryption mode is enabled for that host, an encrypted core dump is generated and the host reboots. The core dump is encrypted with the host key that is in the ESXi key cache. This key comes from the KMS and is an AES-256 key, see How vSphere Virtual Machine Encryption Protects Your Environment for some background information. What you can do next depends on several factors.
In most cases, vCenter Server retrieves the key for the host from the KMS and attempts to push the key to the ESXi host after reboot. If the operation is successful, you can generate the vm-support package and you can decrypt or re-encrypt the core dump. See Decrypt or Re-Encrypt an Encrypted Core Dump.
If vCenter Server cannot connect to the ESXi host, you might be able to retrieve the key from the KMS. See Resolve Missing Key Issues.
If the host used a custom key, and that key differs from the key that vCenter Server pushes to the host, you cannot manipulate the core dump. Avoid using custom keys.
Core Dumps and vm-support Packages
Core Dumps on vCenter Server Systems
A core dump on a vCenter Server system is not encrypted. vCenter Server already contains potentially sensitive information. At the minimum, ensure that the Windows system on which vCenter Server runs or the vCenter Server Appliance is protected. See Securing vCenter Server Systems. You might also consider turning off core dumps for the vCenter Server system. Other information in log files can help determine the problem.