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Why PieTTY echo login password as "*"?

 
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Top Forums UNIX for Dummies Questions & Answers Why PieTTY echo login password as "*"?
# 1  
Old 08-06-2011
Why PieTTY echo login password as "*"?
Normally, When we login a remote server, the password does'nt echo as anything. But When I use PieTTY(on windows) to login a linux ssh server, the password echoes as "*". But When I have logged in, I use the ssh command to login the same server locally again, now the password does'nt echo.

I know we can use tcsetattr() and set the terminal to NO ECHO in a programme when we need a password. But in the case above, it is a bit confusing. Any idea?

PS: PieTTY is a fork of PuTTY. But PuTTY does'nt echo passord in any condition.

Code:
login as: admin
password: ********                //echo "*" here
[admin@Archlinux~] ssh 127.0.0.1
password:                         //echo nothing here
[admin@Archlinux~] exit
Connection to 127.0.0.1 closed.
[admin@Archlinux~]

Last edited by vistastar; 08-06-2011 at 04:39 AM..
# 2  
Old 08-06-2011
I assume you are connecting through Windows. So during your first login, prompt is of windows which generally displays the passwords in * from.
Once you are logged into UNIX (archlinux), stty settgins are set, so that they dont display password while you type them
# 3  
Old 08-06-2011
I'd say it's a setting of PieTTY, since the output during the connection phase is completely controlled by the client. There's no server or console setting that would influence that.
# 4  
Old 08-07-2011
@ a20786

Why stty settings are set after login? When we are logining, we are in a terminal already.

@ pludi
I am sure that the sshd has control to the terminal to decide if the password should be echoed. There's no option in the PieTTY setting panel about this. I assume the windows ssh client PieTTY negociates with sshd to display a "*". When logged in, the linux ssh client negociates with sshd to display nothing. But I'm not sure.
PS: Since PieTTY surpports telnet too, I tried to telnet to the server, It does'nt display password as "*".
Last edited by vistastar; 08-07-2011 at 02:32 AM..
# 5  
Old 08-07-2011
I skimmed through the Authentication RFC (RFC 4252) again, and didn't see anything about negotiation of password echoing.

Also, there's a big difference between SSH and Telnet: as soon as you connect to a telnet server, it controls the connection and all output. So if the telnet server decided that you should see asterisks when entering the password, you will see them. If it decides you should see percent signs instead, you'll see those.

And no, when you're still authenticating in SSH, you don't have a terminal yet. You're connected to the SSH server, which usually runs as a daemon, and doesn't have a TTY associated. Only after successful authentication the connection is assigned a TTY (if the client requests one).
# 6  
Old 08-07-2011
Quote:
I skimmed through the Authentication RFC (RFC 4252) again, and didn't see anything about negotiation of password echoing.

Also, there's a big difference between SSH and Telnet: as soon as you connect to a telnet server, it controls the connection and all output. So if the telnet server decided that you should see asterisks when entering the password, you will see them. If it decides you should see percent signs instead, you'll see those.

And no, when you're still authenticating in SSH, you don't have a terminal yet. You're connected to the SSH server, which usually runs as a daemon, and doesn't have a TTY associated. Only after successful authentication the connection is assigned a TTY (if the client requests one).
Agree with you. I read APUE in chapters about the terminal, It is really complex about TTY.
In experiments I find telnetd involks 'login' and assigns TTY to it, but sshd verifies passwords itself with no TTY.
But since I can communicate with sshd without a TTY, what does a TTY really do? What is the relationship between ssh client and the terminal emulator?
# 7  
Old 08-07-2011
A TTY is basically a software emulated computer terminal. In the olde days it was common that multiple terminals were connected to a mainframe using serial cabling (it's from that time that there's a distinction between the Return key and the Enter key). A daemon doesn't need a terminal to work, since it doesn't do any direct interaction with the user. Other programs however do need it, as the TTY provides the input and output channels that the user interacts with.
This User Gave Thanks to pludi For This Post:
vistastar
 
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