== Extract a certificate from PKCS#12 / .pfx / .pkcs12 ==

Using openssl:

{{{
openssl pkcs12 -in infile.p12 -nokeys -out outfile.pem
}}}

This exports all certificates contained in infile.p12 to outfile.pem in PEM format. You have to enter the password used to create the PKCS#12-file. For more infos see also http://www.openssl.org/docs/apps/pkcs12.html

== Extract a public key from a certificate ==

Ugh, why do you need a public key without the certificate? Anyway, using openssl with

{{{
openssl x509 -in mycert.pem -noout -pubkey
}}}

prints the public key to stdout in PEM format. See also http://www.openssl.org/docs/apps/x509.html

== Merge a certificate and a private key into a PKCS#12 ==

Using openssl:

{{{
openssl pkcs12 -export -in certs.pem -inkey key.pem -out outfile.p12
}}}

merges all certificates from certs.pem with the key in key.pem into the PKCS#12-file outfile.p12. See http://www.openssl.org/docs/apps/pkcs12.html

== Backup a certificate ==

Export it from your browser/mailer/application into a PKCS#12 file and store the file safely. How to export depends on your application.

=== Mozilla / Seamonkey ===

Open the certificate manager: Edit->Preferences...->Privacy & Security->Certificates->Manage Certificates...

Press "Backup all" or select a specific certificate and press "Backup"

=== Thunderbird ===

Open the certificate manager: Edit->Settings->Privacy->Certificates

Press "Backup all" or select a specific certificate and press "Backup"

=== Firefox ===

Just like Thunderbird IIRC.

=== Internet Explorer / Windows ===

Use the "Internet Oprions" applet from the control panel, click on the "Certificates..."-Button of the "Content" tab. Select the certificate and press "Export...". Select "Yes, export private key" and PKCS#12 as the file format. If you cannot select this "Imporved Security" is activated, and there is no way for you to export the pricate key. At least no simple one. Bad luck.

I'd advise to deactivate the "Improved security" Checkbox. AFAIK this prevents that the private key can be exported again if the file is imported once more.

== Restore a certificate ==

Usually the "Import"-Button for PKCS#15-Files is quite close to the "Export"- or "Backup"-Button.