What's the difference between certificate and credentials?

Question

What's the difference between digital certificate (e.g. .pem or .der files) and credentials (e.g. .pfx files)?

Answer 1

Unlike plain certificate files, credentials files (often packaged as PKCS#12 files: .p12, .pfx) also include the private key that forms a matched set with the public key in the certificate.

Certificates are public documents you give to everyone, like business cards. They're a way to reliably link your identity information (your name and email address, or your web server's fully-qualified domain name) to your public key.

Since you give out your certificate to everyone, merely possessing or presenting a certificate is not proof that you're the rightful owner of that certificate. The way to do that is to prove you know the secret private key that matches the public key in the cert. So you can't use a certificate as proof of who you are (authentication credentials) unless you have the private key that goes with it.

So when you package a cert along with its matching private key, it's referred to as credentials.