Tutorial - Using Host-Based Authentication for an SFTP Server

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Stonebranch
Last updated: Sept 30, 2022

In this tutorial, you will:

  • Configure a local SFTP server to allow host-based authentication for certain accounts.

  • Check that the server is refusing to serve connections for invalid combination of account and keys.

  • The client connection is performed by UDMG client partner as explained in the Tutorial - Using Host-Based Authentication for an SFTP Partner.


To configure host-based authentication for an SFTP server, several configuration parameters are set to mimic the behaviour of the known_hosts and .shosts files in a traditional SSH environment, where the public keys and the authorized users for a given client host are configured.

Step 1

From the UDMG navigation pane, select Management > Servers. The Server list displays.

Step 2

Select the stonebranch-sftp-01 server and note the address 0.0.0.0 and port 4000 on the Server details tab.

Step 3

Select the Configuration tab and click on the add button (with the plus sign) next to the Host-based authentication label. A Client Details window appears:

Step 4

  • In Host Name field, input a comma separated list of the hostnames or IP addresses that are allowed to authenticate using this public key.

    hostnames are matched without considering the port, so there is no need to specify the incoming port (e.g.: hostA.example.com should be used instead of [hostA.example.com]:2222 for a server running on port 2222).
    For the tutorial, type 0.0.0.0

  • In Key Algorithm field, the algorithm used to generate the public key: ssh-rsa

  • In Public Key field, paste the client public key: from the file stonebranch-client-01.crt.pub, only the key value without the comment and the algorithm label

  • In Account field, select a server local account for which the host-based authentication will be enabled for connection from this client: stonebranch-01

  • In the Remote Users field, input a list of remote users which are allowed to connect to this local account: stonebranch-01

  • Additional mappings of local accounts and remote users can be added with the ‘plus’ button.

Step 5

Click Confirm to close the Client Details window

Step 6

Click Save and Confirm to store the updated server configuration

Step 7

Restart the MFT Waarp Gateway service.

For exmple on Linux:

systemctl restart mft_waarp_gateway

The local SFTP server is restarted with the new configuration and the restricted list of encryption algorithms.

Step 8

Verify that the server accepts host-based authentication attempts:

$ sftp -v \
-o "PubkeyAuthentication=no" -o "PasswordAuthentication=no" \
-o"HostbasedAuthentication=yes" -o "HostbasedKeyTypes=ssh-rsa" \
-P 4000 stonebranch-01@0.0.0.0 2>&1 |grep hostbased
debug1: Authentications that can continue: password,publickey,hostbased
debug1: Next authentication method: hostbased
debug1: userauth_hostbased: trying hostkey ssh-rsa SHA256:CYzKciuXNJBKSolgD6F/fQZOXDd6tObHz/d1x4E0OgA
debug1: Authentications that can continue: password,publickey,hostbased
debug1: No more client hostkeys for hostbased authentication.
Permission denied (password,publickey,hostbased).


Step 9

To verify the connection to the local UDMG server, either configure your favorite SFTP client with the client key and the parameters that are defined on the server in Step 4

or follow the tutorial “Tutorial - Using Host-Based Authentication for an SFTP Partner” on how to setup a UDMG remote partner with host-based authentication and perform sample file transfer between the UDMG server and partner.

References: