telnets

User interface to the TELNETS protocol. TELNETS is the secure version of the TELNET protocol.

TELNETS is the TELNET protocol over a secure TLS (or SSL) connection.

Usage

telnets host [port]

TELNETS vs SSH

Note that TELNETS and SSH are not the same thing.

SSH is considered a secure alternative to the (un-secure) TELNET protocol. (And note that is "TELNET" without an "S" at the end.)

TELNETS (with an "S" at the end) is the secure version of (un-secure) the TELNET protocol.

What does the "S" at the end mean?

The "S" at the end of "TELNETS" stands for "secure". Just like the "S" at the end of "HTTPS".

openssl ?

But wait... you might be thinking... isn't TELNETS the same as call to openssl s_client -host $1 -port $2?

Absolutely not!

The TELNET and TELNETS have special binary escape codes and control codes that openssl does not understand, and won't be able to handle properly. And will lead to corruption of the data stream!

For example, in the TELNET and TELNETS protocols, byte value 255 has a special meaning, and is called IAC (which is short for "interpret as command").

If byte value 255 is sent as data, then it must be "escaped" by having two IACs in a row. (So IAC becomes IAC IAC; or in other words 255 becomes 255 255.)

If this is not done, it will corrupt the TELNET and TELNETS data stream!

But that is just one example. The following is also a control sequence: 255 251 24. (This happens to mean IAC WILL TERMINAL-TYPE.)

If this happens to be in the data, then it must be "escaped" properly, or it will corrupt the TELNET and TELNETS data stream.