The first column in this field allows you to select the authentication type for this export. The options are :

sys
  Old-style NFS IP or network based security, which is enforced entirely by the client IP address.

krb5
  Kerberos authentication (requires that the client and server systems have Kerberos configured).

libkey
  The LIPKEY security mechanism.

spkm-3
  SPKM3 authentication mechanism.