SecSign ID Plugin: FTP PAM

Please read the SecSign ID PAM Tutorial before using the SecSign ID PAM for SSH Authentication. Follow steps 3 to 5 to configure and install PAM correctly.

Note: Using the FTP protocol without additional security measurements results in unencrypted data transfer and is regarded as unsafe. Passwords and other data are transmitted in plain text and can be wiretapped. Using FTP with SSL/TSL generates encrypted data transfer with FTPS and the SecSign ID Two-Factor Authentication acts as additional security measurement.

Since there are several ways to encrypt FTP connections we use the term FTP in the following tutorial – an encrypted connection is implied, even with the additional protection of the SecSign ID Two-Factor Authentication eliminating the thread of user data compromise.

We use the common FTP server “ProFTPd” for this tutorial. Other FTP server, for example “vsftpd” support PAM as well and are connected as or similar to the following description.

Overview on the configuration and installation:

1. libcurl and gcc are required
2. inquire SecSignID PAM and unpack
3. Adjust the path to the configuration file in secsign.c
4. Add all user names and corresponding SecSign IDs in secsignid.config
5. make
6. Copy the compiled file pam_secsignid.so in the PAM library (usually /lib/security)

Install the ProFTPd as standalone version via apt-get install proftpd openssl. Open the configuration file/etc/proftpd/proftpd.conf and adjust all envirnomental settings for the FTP like data transfer via TLS.

The ProFTPd configuration script verifies the system’s support for PAM and runs mod_auth_pam automatically.

With other FTP server (like “vsftpd”) you may have to stare the utilization of PAM manually.

To grant the user some time to accept the login on his smartphone the values in TimeoutNoTransfer, TimeoutStalled und TimeoutIdle should be extended accordingly, providing at least two minutes.

Open the configuration file for the ProFTPd PAM settings/etc/pam.d/proftpd and change the following parameter:

#%PAM-1.0
auth [success=1 default=ignore] pam_secsignid.so
auth requisite pam_deny.so
auth required pam_permit.so
#auth required pam_listfile.so item=user sense=deny file=/etc/ftpusers onerr=$
#@include common-auth 

Save the file and reboot the FTP server by employing service proftpd restart.

In the next step the FTP server can be tested. Please adjust the timeout value in the FTP client program (for example FileZilla) to two minutes to allow the user to accept the session on his smartphone.

Compilation errors

The library libcurl needs to be installed in the standard path, otherwise make fails. If libcurl is not on the standard path the compilation needs to be executed manually.

Authentication errors

If the authentication fails the debug- and logmodus should be activated (see PAM debug- and logmodus) and the output should be written in a file. This is necessary since PAM normally needs to be silent and does not allow for output for security reasons. If no log- or debug-files are generated the paths provided in secsignid.c are incorrect or no read-and-write authorizations are available.

A log-file is produced stating all errors. It is determined if libcurl works accurate, if the SecSign ID server is available, if port 443 is available to communicate with the server, if the configuration file is available and if PAM has reading authorization.

A debug file is created which records the interface communication. It is determined wether errors in the communication persists because no SecSign ID for the specific user was found or if there are errors in a different parameter, for example the service name.