If your organization’s VPN or Wi-Fi networks rely on secure certificates, you must obtain the certificates and store them in your phone’s secure credential storage, before you can configure access to those VPN or Wi-Fi networks on your phone.
If your network administrator instructs you to download the certificates from a website, you’re prompted to set a password for the credential storage when you download the certificates. For more information about working with credential storage, see Location & security settings.
Android supports DER-encoded X.509 certificates, saved in files with a .crt file extension (if your certificate file has a .cer, .der, or other extension, you must change it to .crt 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 extension (if your key store has a .pfx or other extension, you much change it to .p12 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 contained in the key store.
Copy the certificate from your computer to the root of its USB storage or SD card (that is, not in a folder).
Press Home , press Menu , and touch Settings, to open the Settings application.
Touch Location & security.
Touch Install from USB storage or Install from SD card (depending on your model of phone).
If you have not already set a password for your phone’s credential storage, you’re prompted to enter a password for it twice and then touch OK. For more information about credential storage, see Location & security settings.
You can now use the certificate that you installed when connecting to a secure network. For security, the certificate is deleted from the USB storage or SD card.