torproject.org has public-key pinning in Chrome, although without the "More" information I can't tell whether it's a pinning error or just that your ISP is blocking the site.
to get the certificates that are coming back. You can copy and paste a "-----BEGIN CERTFICIATE-----" ... "-----END CERTIFICATE-----" block into `openssl x509 -text -noout` to get a dump.
I would guess that it's a self-signed certificate fronting a "sorry, this site is blocked" page.
You can try running:
$ openssl s_client -connect blog.torproject.org:443 -showcerts > /tmp/log
to get the certificates that are coming back. You can copy and paste a "-----BEGIN CERTFICIATE-----" ... "-----END CERTIFICATE-----" block into `openssl x509 -text -noout` to get a dump.
I would guess that it's a self-signed certificate fronting a "sorry, this site is blocked" page.