Developing secure coding in Azure Sphere


This article was originally published by Jewell Seay in the Internet of Things blog


"How do you develop secure code?" I've been asked this a lot recently and it is time for a blog post as the public and various parts of Microsoft have gotten a glimpse of how much Azure Sphere goes through to hold to our security promises. This will not be a short blog post as I have a lot to cover.


I joined Microsoft in February 2019 with the goal of improving the security posture of Azure Sphere and also desired to give back to the public community when possible. My talk at the Platform Security Summit talks about the hardware however the talk did not provide detailed answers on how to improve security for software development and testing. Azure Sphere's focus is IoT however we still give back to the open source community and want to see the software industry improve too, this blog post is to help reveal the efforts we go through and hopefully help others understand what it means to sign up saying you are secure.


First, you must realize that there is no magic bullet or single solution to keep a system secure, there are a wide range of potential issues and problems that require solutions. You must also accept that all code must be questioned regardless of where it is from, so how does Azure Sphere handle this? We have a range of guidelines and rules that we refuse to bend on. These become our foundation when questions come up about allowing an exception or if a new feature has the right design by checking if it violates a rule we refuse to bend on. The 7 properties is a good starting point and provides a number of overarching requirements, this is further extended with internal requirements that we do not want to bend on, an example being no unsigned code can ever be allowed to execute.


What is your foundation? What lines are you willing to draw in the sand that can not be compromised, bent, or ignored? Our foundation of what we deem secure is always being improved and expanded with the following being a few examples. These are meant to help drive thoughts on what works on your own software and is not meant to be a complete list. By having these lines along with the 7 properties allows for better security decisions as new features are added.


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