Documentation/config/extensions.txt

   1 extensions.objectFormat::
   2         Specify the hash algorithm to use.  The acceptable values are `sha1` and
   3         `sha256`.  If not specified, `sha1` is assumed.  It is an error to specify
   4         this key unless `core.repositoryFormatVersion` is 1.
   5 +
   6 Note that this setting should only be set by linkgit:git-init[1] or
   7 linkgit:git-clone[1].  Trying to change it after initialization will not
   8 work and will produce hard-to-diagnose issues.