linuxexpert-practice-labs/labs/linux-plus/3-5-3-hashing-and-certificates

Linux+ 3.5.3: Hashing and certificates

A checksum that catches a change, a private CA and a server certificate it signs, and trusting the CA system-wide.

Before you start

Nothing is set up. Work as root (sudo -i), in root's home directory /root, so the files are where the check looks: /root/f.txt, /root/f.sha256 and /root/pki/.

Tasks

1. Write version 1 to f.txt, save its SHA-256 checksum in f.sha256, and check it. Then change the file to version 2 and see the check fail. Leave it like that.
2. In /root/pki, make a private CA (ca.key, ca.crt, subject CN=Lab CA), and a server key and certificate (www.key, www.crt) for lab.example.test, with that name in its subject alternative names, signed by the CA. Verify the certificate against the CA.
3. Serve the certificate with openssl s_server on port 8443 and see curl reject it, then accept it with --cacert. Then add the CA to the system's trust store, and see curl accept it without --cacert.

Hints

• sha256sum FILE > FILE.sha256, sha256sum -c.
• openssl req -x509 -newkey rsa:3072 -nodes, openssl req -new, openssl x509 -req -CA -CAkey -CAcreateserial -extfile with subjectAltName=DNS:...; openssl verify -CAfile.
• curl --resolve lab.example.test:8443:127.0.0.1. RHEL family: /etc/pki/ca-trust/source/anchors/ and update-ca-trust; Ubuntu: /usr/local/share/ca-certificates/ (the name must end in .crt) and update-ca-certificates.