The file ca-bundle.crt contains certificates extracted from Microsoft Windows. These are installed and used as the default trusted root certificates when SSL certificate verification is requested with --ssl-verify. On some platforms (some Unixes), these certificates are used in addition to any certificates installed by the operating system. Microsoft's bundle was preferred over Mozilla's because Microsoft may be more selective in the organizations it trusts. When this bundle was created, Microsoft's store had 107 certificates while Mozilla's had 126. See below for how to use an alternative trust store. == How to extract the trusted root CA certificates on Windows These instructions require the openssl command-line utility. On Windows XP, run the rootsupd.exe tool to downoad the full list of trusted certificates. Otherwise there is only a partial list (certificates are downloaded on demand). http://support.microsoft.com/kb/931125 http://www.download.windowsupdate.com/msdownload/update/v3/static/trustedr/en/rootsupd.exe Press "Start", then "Run...". Type "certmgr.msc" and press Enter. Open the folder "Trusted Root Certification Authorities" and its subfolder "Certificates". Click on "Expiration Date" to sort. Select the first certificate that is not expired, then press Shift+down arrow until all the non-expired certificates are selected. Right-click on the list of certificates, and in the context menu, select "All Tasks", then "Export...". Export to the file ca-bundle.p7b. In a Cygwin shell, enter the directory containing ca-bundle.p7b and run the command openssl pkcs7 -in ca-bundle.p7b -inform der -print_certs -out ca-bundle.crt That will create a file ca-bundle.crt containing all the certificates, each preceded by its subject and issuer. == Alternative sources for a certificate bundle Another commonly used trust store is the one provided by Mozilla. The cURL package includes a script that automatically creates a suitable PEM file from a file in Mozilla's source repository. They also provide ready-made PEM files to download. See http://curl.haxx.se/docs/caextract.html. Here is how to download Mozilla's trust store: $ wget https://raw.github.com/bagder/curl/master/lib/mk-ca-bundle.pl $ perl mk-ca-bundle.pl