Friday, 16 May 2014

Should OpenSSL be Considered Safety Critical Software?


I'd like to make a case that OpenSSL should be considered safety-critical software.


Thanks to qlkzy, Andrew Stevens and my other half for proof-reading my initial drafts of this and offering valuable feed back.

Safety Critical

Safety critical software is a system in which the failure of the software would lead to a "safety loss event". That is, if it all went to shit, there would be a loss of life, injury or major property loss.

The medical, automotive, aerospace and rail industry are all quite good at delivering high integrity software, and over the billions of operational hours, the number of defects is incredibly low. Although, the number of defects is non-zero, and lives have been lost.


OpenSSL is a library which is used world-wide to ensure the confidentiality and authenticity of communications. That is, no one can read your communication, and no one can tamper with it.

It is most commonly used to secure communications between a client's web browser and a web server. To most people, this just means that their Facebook password remains from safe prying eyes when sent to Facebook.

We can look at some not-too-unrealistic scenarios in which the safety of life and limb are placed in OpenSSL's hands.

Becoming a Critical System

Here are a few scenarios that, although they rely on social effects, are very much protecting the life of their user.

Scenario 1

A person who is in an abusive relationship attempts to find resources on the internet that will help them leave the relationship. Most likely, their Google searches will be protected from prying eyes by the fact that their searches are protected by an SSL connection, provided courtesy of OpenSSL.

If the abusive partner finds out about them seeking help, it may end with the victim being forced out of their home, or further abuse or violence from their abusive partner.

Scenario 2

A member of the LGBT community would like to get support or friendship from other members of their community whilst living in a country where being an LGBT person could result in death (for example, Uganda), or living with family who would ostracise an LGBT member (especially problematic for youngsters with no income or home of their own).

The person could use a fake Facebook profile or Reddit account to connect with other LGBT people, and put themselves at serious risk, were their communications not sufficiently protected. Should OpenSSL fail, these people could be killed or forced out of their homes.

Scenario 3

Almost all banks use SSL connections to secure their online-banking facilities.

Assuming that they use OpenSSL (and they will at some level, most web-browsers use it), then the potential damage to the economy of a large-scale failure is massive.

Scenario 4

A political dissident uses The Onion Router (TOR) to hide their identity and make their opinion of the government known in a country where the price of dissent is death.

TOR currently uses OpenSSL to protect its communications. Should this fail for those users, there would be serious implications for their users, including prosecution, torture or death.

Scenario 5

This is definitely my most out-there scenario, but it could arise, especially in countries where the safety regulations are much more lax.

A nuclear power station is remotely monitored with some control being off-site (e.g. night shifts, etc.)

If the control communications were protected by OpenSSL, and could be interfered with in any way, this could obviously lead to a major ecological disaster, loss of life and serious health issues for the local population.


I hope I've made it clear that I consider OpenSSL (and similar libraries) to be safety critical software, since it is being used to protect life and sizeable swathes of the economy.

I feel strongly that, like a good police force, your safety should be free and available to all regardless of who you are.

Unfortunately, we do not currently treat them as such. There is limited auditing in OpenSSL, and the only SSL library that has had any in-depth review is PolarSSL, and that is not free for commercial applications. This means that commercial systems (e.g. banks) will be less likely to use the verified implementation when a free, more well-known implementation is available.