gitlab-org--gitlab-foss/doc/security/ssh_keys_restrictions.md

Restrict allowed SSH key technologies and minimum length

ssh-keygen allows users to create RSA keys with as few as 768 bits, which falls well below recommendations from certain standards groups (such as the US NIST). Some organizations deploying GitLab will need to enforce minimum key strength, either to satisfy internal security policy or for regulatory compliance.

Similarly, certain standards groups recommend using RSA, ECDSA, or ED25519 over the older DSA, and administrators may need to limit the allowed SSH key algorithms.

GitLab allows you to restrict the allowed SSH key technology as well as specify the minimum key length for each technology.

In the Admin area under Settings (/admin/application_settings), look for the "Visibility and Access Controls" area: