Read you FAQ
https://whonix.org/wiki/FAQ#Why_aren.27t_you_using_OpenBSD.2C_it.27s_the_most_secure_OS_ever.21.21.211.21
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There doesn't seem to be a modern MAC, instead there's systrace which has been criticized for having fundamental security problems (this may or may not have changed since then)
Why don't you take a FreeBSD? There is a complete modern MAC.
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OpenBSD is also a very small OS (small TCB),
It is not a Linux zoo, you right. It is secure focused OS.Quote
OpenBSD's target audience aren't end users, that's why they don't care to provide signed updates for the masses, see How to check downloaded package on OpenBSD 5.1?.
OpenBSD produce OpenSSH, there is rsync gateway for download packages, also there is AFS(Andrew File System) with alot of mirrors of OpenBSD repositories.
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OpenBSD's website isn't reachable over SSL or as a Tor hidden service. How are users supposed to securely view the OpenBSD site and not learn things set up by a man-in-the-middle?
You develop over TOR, Do you know how it can help you browse OpenBSD's website? You still worry about the middle?
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"buy the CDs"
Let me tell you once again, look at AFS( Andrew File System ).
Anyway, Linux - is a great choose, too. Good luck you with your job!