Watch a password cross a café network in plain ASCII — one byte at a time.
- mode
- character-at-a-time
- who echoes
- — not yet agreed —
- segments so far
- 0
- header : payload
- 41 : 1
- encryption
- none
- credentials captured
- — none yet —
server echoes every keystroke
one round trip per keystroke
one per keystroke, plus echo
40+ bytes of IP/TCP wrap each payload
no TLS, no key exchange, ever
the tap is waiting
Telnet has no login protocol of its own. What does the client do first?
Character mode is Telnet as most people meet it. Every keystroke is a packet, and the letters on your screen came back from the server. Open the session and watch the tap.
Telnet is not simply “SSH without encryption.” It is a negotiated byte stream: before one character of your password moves, the two ends argue about who echoes, whether to suppress go-ahead, and what terminal you claim to be — in IAC command bytes interleaved with your data.
The echo is not local. In character mode the server sends your own letters back to be printed — which is why a laggy link types laggily, and why one keystroke costs two segments.
Line mode fixes the chattiness. It does not fix the exposure — the tap reads the password either way. Only a different protocol underneath does that: see the HTTPS lab for what a real encrypted channel costs, and the TCP lab for the stream beneath.
Watch a password cross a café network in plain ASCII — one byte at a time.
- Why can anyone on the network read the Telnet password?
- In character mode, why does typing “admin” take ten segments?
Read it now and keep it in mind — the answer is in what you are about to watch.