Lesson 4.8: Remote access, and the protocols that send passwords in the clear
How administrators reach other machines, and why the protocol matters: Telnet and FTP send everything, passwords included, as readable text; SSH encrypts everything and proves the server's identity with a host key. Host key fingerprints and trust on first use. In the lab you find which login services a NAS offers, read a Telnet and an FTP password straight out of captured traffic, compare it with an SSH capture, and check an SSH host key against its known fingerprint.
18 min
You will learn to
- Explain cleartext protocols and why they're dangerous
- Read credentials from a Telnet and an FTP capture
- Explain what SSH protects
- Explain host key fingerprints and trust on first use
- Recommend secure replacements
Key terms
- Remote access
- Using a machine over the network as if you were at its keyboard, or moving files to and from it.
- Cleartext protocol
- A protocol that sends data, including passwords, without encryption, so anyone on the path can read it.
- Telnet
- An old remote terminal protocol (TCP 23) with no encryption at all.
- FTP
- An old file transfer protocol (TCP 21) that sends user names, passwords and files in clear text.
- SSH
- The encrypted replacement for Telnet and friends (TCP 22): remote login, commands and file transfer, with the server proving its identity.
- Host key fingerprint
- A short hash of an SSH server's public host key, used to check you're connecting to the right server.
- Trust on first use (TOFU)
- Accepting a server's key the first time and warning if it ever changes. Safe only if that first time is checked.
- Sniffing
- Capturing traffic on a network to read what passes by.
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