Artifactory natively supports SHA-256 starting Artifactory 5.5.
Artifactory servers initiated at version 5.5 or above are automatically SHA-256 ready, and any new artifact deployed into Artifactory 5.5 or above has its checksum SHA-256 calculated.
However, artifacts that were already hosted in Artifactory prior to the upgrade will not have their SHA-256 checksum in the database yet.
To make full use of Artifactory's SHA-256 capabilities, you need to run a process that migrates Artifactory's database making sure that the record for each artifact includes its SHA-256 checksum.