There is only one file type that uses the .KEYTAB extension:
Kerberos Keytab File
Keytab file created and used by Kerberos, a network authentication protocol; contains pairs of Kerberos principals along with an encrypted copy of that principal's key.
The KEYTAB file is used to authenticate a principal on a host to Kerberos without any user interaction or having to store a password in a plain text file. The file is encrypted but should be secured well because whoever has access to the file can act as that principal.
Kerberos provides authentication tools and secret-key cryptography to secure communications by client/server applications. The Massachusetts Institute of Technology (MIT) has made a free implementation of the protocol available in source form. The protocol is also available in a variety of commercial products.
krb5.keytab - Keytab file used by a Kerberos server machine to authenticate the Key Distribution Center (KDC) network service.
Updated: October 21, 2015