Google Galaxy Nexus Android mobile technology platform 4.0 Users Guide - Manual (Page 105)

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Work with certificates
You can use digital certificates to identify your device for a variety of purposes, including VPN or Wi-Fi
network access as well as authentication to servers by apps such as Email or Browser. To use a
certificate to identify your device, you must obtain it with help from your system administrator, and install
it in your device's trusted credential storage .
Android supports DER-encoded X.509 certificates, saved in files with a .crt or .cer file extension. If your
certificate file has a .der or other extension, you must change it to .crt or .cer or you won't be able to
install it.
Android also supports X.509 certificates saved in PKCS#12 key store files with a .p12 or .pfx extension. If
your key store has some other extension, you much change it to .p12 or .pfx or you won't be able to install
it. When you install a certificate from a PKCS#12 key store, Android also installs any accompanying
private key or certificate authority certificates.