SSL in Wikipedia 
The public SSL certificate authority system is not to be trusted. Too many security breaches happened before. 
See also Man-in-the-middle attacks.
Whonix Technical Design
SSL certificates, especially for https://check.torproject.org (check.tpo) are not yet pinned in Whonix. Eventually that will be done in future. That needs some more discussion. How that technically could be done is documented under Dev/SSL Certificate Pinning. This has low priority for Whonix, since not even the Tor Browser Bundle does pin the check.tpo SSL certificate, which is a much bigger issue. Whonix developer adrelanos does not agree with "low priority" in TBB. See TBB: hardcode SSL cert check to prevent MITM.
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