certificates

By mistake we have been using key1 for some of our security settings.
Now key1 is going to expire.
I have solved the issue for the encryption and signing key.
But it seems that we also used the key for ssl.
Does anyone know what kind of key we have to load for the ssl? I can load cer files, but do not know if this is the right kind.
What kind of certificate should I sent to the partner? cer? pb7, ? pfx? an other type?

Foren
AS2