SFTPPlus on the OSI

The OSI model is a model that characterizes and standardizes communication functions. The layers range from layer 1 right through to layer 7. In the OSI, or Open Systems Interconnection model, SFTPPlus sits in the OSI Layer 7 or on the application layer.

The application layer sits at the top of the OSI model and is the software, hence the name application, layer between the end-user and the networking layers underneath.

Introduction

When you create file transfer systems that interact with services, protocols, databases, users and data, it is important to ensure that the system is being protected and monitored from unauthorized modifications, use, access or destruction.

Ensuring that activities are under proper monitoring and logging is also an important aspect of secure file transfer infrastructures. Should there be access attempts from that particular IP range? Should this file transfer service port be in use at all? Are there subsets of data that are critical enough that an alert mechanism be put in place for failed transfers in that source? The answers to questions like these will help provide the basis for meeting logging and auditing requirements for your infrastructure through our audit and logging mechanisms.

Potential use case for HTTP Authorization

A potential use case for the API is utilizing the HTTP Authorization for SFTPPlus. This is deployed in a DMZ where certificate-based authentication cannot be used, only a username/password authentication with a time limit expiration.

Case study with load balancers and HTTPS push from third party via SFTPPlus API

This case study involves integrating with a third party. In this case, the third party is a web application functioning as the client.

Through the HTTPS service that is available with SFTPPlus, the third party developer works with the SFTPPlus HTTP API to authenticate the users and to allow them to upload content (push) to the SFTP servers.

Subsequently the corporate, or internal network, are authenticating via the SSH key exchange (as one of the possible methods) and pulling content from the servers.

While the topic is covered in another article, the servers are also set up for high availability and resilient environment via a load balancer. In this case, the load balancer is utilizing the weighted round-robin algorithm depending on the server ‘weight’.

Ensuring high availability is also a pathway to secure file transfer operations by making sure that critical data is constantly available. Load balancers can be used with SFTPPlus to set up high availability.

Through a combination of choosing secure file transfer protocols, smart use of the SFTPPlus API and structuring file transfer operations to function in a high availability environment, you can further secure your data and file transfers with your company.

Case study with DMZ and buffer zones

For a case study on how SFTPPlus is integrated with a DMZ, see above for an example of an internal company user transferring files towards external, public-facing servers.

In this case, the FTP/SFTP ‘Inbox’ folder which resides within the DMZ will utilize the SFTPPlus file-dispatcher Event Handler to dispatch files to the ‘Outbox’ folder within the DMZ.

The file-dispatcher event handler has been configured to move files from the SFTPPlus Inbox folder to the SFTPPlus Outbox folder based on a matching expression - either global or regular expression. In this instance, we can say that the matching expression is for all PDF files. All of this happens with the DMZ which acts as a buffer zone between the media PC in an internal network to external servers.

From the SFTPPlus Outbox folder, which serves as a cache of matched files, users can initiate a client transfer to the external public facing servers outsize the DMZ.

Accounting part of the AAA framework

As SFTPPlus operates, it will emit a set of events which contains a unique ID and defines a specific operation carried out by the server. A common action for an event is to send it to one of the supported logging systems. This covers the Accounting requirement of the AAA (Authentication, Authorization, and Accounting) security design framework.

Utilizing an accounting, also seen as auditing, framework is a way to ensure that any compliance or logging obligations and requirements are met.

Authorization part of the AAA framework

The use of authorization is one of the fundamental aspects of network and resource management security. By building an authorization framework, you can ensure that users have correct access to network resources.

In the above diagram, we have two users in the same department or user group but both of these users have different access requirements. After authentication via the authentication server, how does an administrator ensure that the correct authentication framework is applied? One user can only have read-only rights to shared folder and full-control for a common home folder. Whereas another user has full-control-allowed access to both the common folder and all other folders underneath, including a shared folder with the first user.

In the above diagram, the permissions framework can be set up on a global or on a per-path basis, including fine-grain details such as permissions for matching expressions.

Even after a user group is authenticated and the correct users are in their respective accounts, a solid authorization framework will ensure that any additional user access rights policies are applied.

Authentication part of the AAA framework

The server-side security of SFTPPlus is designed based on the Authentication, Authorization and Accounting (AAA) components. Authentication can be integrated with external third parties - Windows Domain Accounts - or with external resources such as via the domain controller, via the SSH RSA/DSA keys or SSL certificates.

When compiling how you will secure your system, it is important to take stock of how you are mediating and managing network access based on meeting authentication, authorization and accounting requirements.