Explain the difference between an attack surface and an attack tree

1. Explain the difference between an attack surface and an attack tree. (At least 1
paragraph)

2. Explain the difference between a private key and a secret key. (At least 1 paragraph)

3. Describe and explain, at least, seven different physical characteristics that are used
for authentication in biometric applications. (At least half a page)

4. Explain Federated Identity (Identity Federation) and give an example of how it is used
commercially. (At least 1 paragraph).