I hit the same problem recently when I changed to a brand new Macbook. Even though the solution got few years old, it still worked great. Just minor update for those detail steps in my case. I use a Windows 7 to retrieve certificate.
Windows Specific Instructions:
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6) Click the "Trusted Root Certification Authorities" Tab
7) Find the certificate with the name of the trusted authorities. (Could be your company name or acronym.)
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13) Just use the name of the certificate as the filename.
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That's it. No hassle and it works perfectly on my new Macbook just like before.
Thanks a lot.