Placing certs in /usr/local/share/ca-certificates and running the script didn't work for me on Debian testing x64...
I only needed https://www.thawte.com/roots/thawte_Premium_Server_CA.pem
Downloaded it and copied/renamed as /usr/share/ca-certificates/mozilla/thawte_Premium_Server_CA.crt (needs to be .crt to be recognised). After that I did "sudo dpkg-reconfigure ca-certificates" when asked if I trust new certs I said yes, and then explicitly enabled thawte-Premium_Server_CA which resulted in:
root@hvulin:/etc# dpkg-reconfigure ca-certificates Processing triggers for ca-certificates (20160104) ... Updating certificates in /etc/ssl/certs... WARNING: Skipping duplicate certificate thawte_Primary_Root_CA.pem WARNING: Skipping duplicate certificate thawte_Primary_Root_CA.pem 1 added, 0 removed; done. Running hooks in /etc/ca-certificates/update.d... Adding debian:thawte_Premium_Server_CA.pem done. Updating Mono key store Linux Cert Store Sync - version 4.2.1.0 Synchronize local certs with certs from local Linux trust store. Copyright 2002, 2003 Motus Technologies. Copyright 2004-2008 Novell. BSD licensed. I already trust 175, your new list has 178 Certificate added: C=IL, O=StartCom Ltd., OU=Secure Digital Certificate Signing, CN=StartCom Certification Authority Certificate added: C=ZA, S=Western Cape, L=Cape Town, O=Thawte Consulting cc, OU=Certification Services Division, CN=Thawte Premium Server CA, E=premium-server@thawte.com Certificate added: O=CAcert Inc., OU=http://www.CAcert.org, CN=CAcert Class 3 Root Certificate added: O=Root CA, OU=http://www.cacert.org, CN=CA Cert Signing Authority, E=support@cacert.org Certificate added: C=ZA, S=Western Cape, L=Cape Town, O=Thawte Consulting cc, OU=Certification Services Division, CN=Thawte Premium Server CA, E=premium-server@thawte.com Certificate added: C=US, O="thawte, Inc.", OU=Certification Services Division, OU="(c) 2006 thawte, Inc. - For authorized use only", CN=thawte Primary Root CA 6 new root certificates were added to your trust store. Import process completed. Done done.