SSH

SSH, an acronym for Secure SHell, is a method to securely connect to servers where all data, even the userid and password is encrypted. SSH on iSeries can be used in several scenarios:

• As a server to enable encrypted file transfer and secure remote commands
• As a client to use with other secure servers
• As a secure tunnel to encrypt your regular 5250 telnet sessions

Using the iSeries SSH client

These are instructions on how to use the system i ssh client for automatic, secure file transfer. Your business partner has assigned you a remote user account called yourRemoteUser.

Your local system i process will run as user RUSER.

System Requirements

Full instructions can be found here http://www.ibm.com/servers/enable/site/porting/tools/.

• Portable App Solutions Environment also known as PASE must be installed on the iSeries server to use ssh. Check the existence of licensed program 5722SS1 option 33.
• See also #External links for the IBM Redbook.

Setting up the user profile

Assuming that the user profile to be used is RUSER, you need to set up some folders with the correct permissions.

CHGUSRPRF USRPRF(RUSER) HOMEDIR('/home/RUSER') 
MKDIR DIR('/home') DTAAUT(*EXCLUDE) OBJAUT(*NONE) 
MKDIR DIR('/home/RUSER') DTAAUT(*INDIR) OBJAUT(*INDIR) 

If the home directory already exists, please run

CHGAUT OBJ('/home/RUSER') USER(*PUBLIC) DTAAUT(*EXCLUDE) OBJAUT(*NONE) SUBTREE(*ALL) 

Create the .ssh subdirectory:

MKDIR DIR('/home/RUSER/.ssh') DTAAUT(*INDIR) OBJAUT(*INDIR)

From QShell or QP2TERM command lines, you can set the necessary permissions by executing the following commands:

chmod g-w /home/RUSER
chmod 700 /home/RUSER/.ssh
chmod 600 /home/RUSER/.ssh/authorized_keys

Getting and storing the remote server public key

Log in as user RUSER. You can use a security officer account instead, but then you will have to reset the permissions and file ownership back to RUSER.

Start the PASE shell

CALL QP2TERM 

Execute this shell command

ssh-keyscan -t rsa your.customer.com >> ~/.ssh/known_hosts 

Now you need to set up your own key pair.

Setting up your public and private key pair

Log in as user RUSER. You can use a security officer account instead, but then you will have to reset the permissions and file ownership back to RUSER.

Self Creation of keys

Start the PASE shell

CALL QP2TERM 

Create the appropriate private/public keys with the ssh-keygen tool using an EMPTY passphrase, and place it in the default location in file "~/.ssh/id_rsa".

ssh-keygen -b 1024 -f ~/.ssh/id_rsa -t rsa 

Send the public key from file "~/.ssh/id_rsa.pub" to your customer. ( The public key is added by the sever admin to "~/.ssh/authorized_keys" file on the SSH server.)

Using a key issued by someone else

Your business partner may have issued you a key, and now you should use it and not create your own. In this case, copy the key file that you received into the .ssh folder.

Transferring Files

• A critical difference between most implementations of SCP/SFTP and the PASE environment version is that the commands do _not_ support the -T (tty terminal) switch. This means that authentication by password is _not_ supported.

Instead, you must place your public key on the remote server you intend to connect with.

Copying files with SCP

To copy all xml files from the IN directory on the remote server to the /b2b/incoming IFS folder:

scp -o IdentityFile=~/.ssh/id_rsa yourRemoteUser@your.customer.com:IN/*.xml /b2b/incoming 

(replace "id_rsa" with the actual name of the private key that you are to use) (The /b2b/incoming folder must exist prior to the copying.)

To run batch file transfer via scp, create a script file like this (called examplescp.sh)

#! /QopenSys/bin/sh 
scp -o IdentityFile=~/.ssh/id_rsa yourRemoteUser@your.customer.com:IN/*.xml /b2b/incoming 
exit 

Execute it in batch via command

SBMJOB CMD(CALL PGM(QP2SHELL) PARM('/folderpath/examplescp.sh')) JOB(SSHJOB) USER(RUSER) 

Copying files with SFTP

• Note: the SFTP is not equivalent to the OS/400 FTP client: implicit data conversion is not done (all transfers are binary), nor is there any integration with system security.

We want to copy all xml files from the IN directory (inside our homedir) on the remote server to the /b2b/incoming folder and delete them from the remote server.

Create a text file called ssh-input.txt that contains:

get IN/*.xml /b2b/incoming 
rm IN/*.xml 
exit 

To run batch file transfer via sftp, create a script file like this (called examplesftp.sh)

#! /QopenSys/bin/sh 
sftp –b ssh-input.txt -o IdentityFile=~/.ssh/id_rsa yourRemoteUser@your.customer.com 
exit 

Execute it in batch via command

SBMJOB CMD(CALL PGM(QP2SHELL) PARM('/folderpath/examplesftp.sh')) JOB(SSHJOB) USER(RUSER)

Placing your own public key on the remote server

• These instructions will not work: if your public key is not on the remote server there is no way to log on to that server. It may be possible to do this using a windows or linux based client, that permits password entry.

Sometimes you work with a clueless operator who does not or will not help you to place your public key on the remote server. There is a workaround that requires you to have a valid password for your account (you do have a password, don't you?). You also need write permissions you your home directory, and hopefully it does not have any public authority.

Start the PASE shell

CALL QP2TERM 

Connect to the remote server using your password.

sftp yourRemoteUser@your.customer.com 

Check to see if there is a .ssh folder in your home directory.

dir .ssh 

If it does not exist , create it now, and switch to it.

mkdir .ssh 
cd .ssh 

If the authorized_keys file already exists, then you will have to get it to your system and append your public key to it, and then send it back. If it does not exist, then the following will suffice:

put ~/.ssh/id_rsa.pub authorized_keys

Setting up an iSeries SSHD server

http://www-03.ibm.com/servers/enable/site/porting/tools/openssh.html

To run the sshd daemon on i5/OS:

• The userid that starts the daemon must have *ALLOBJ special authority
• The userid that starts the daemon must be 8 or fewer characters long
• Before starting sshd for the first time, you will need to generate host keys:

ssh-keygen -t rsa1 -f /QOpenSys/QIBM/UserData/SC1/OpenSSH/openssh-3.5p1/etc/ssh_host_key -N "" 
ssh-keygen -t dsa -f /QOpenSys/QIBM/UserData/SC1/OpenSSH/openssh-3.5p1/etc/ssh_host_dsa_key -N "" 
ssh-keygen -t rsa -f /QOpenSys/QIBM/UserData/SC1/OpenSSH/openssh-3.5p1/etc/ssh_host_rsa_key -N "" 

• You can start the sshd daemon with either one of these CL commands:

QSH CMD ('/QOpenSys/usr/sbin/sshd')
CALL PGM(QP2SHELL) PARM('/QopenSys/usr/sbin/sshd')
With IBM i 6.1 you can also use STRTCPSVR *SSHD

• You can stop the sshd daemon at V5R4 by starting the PASE command shell:

CALL PGM(QP2SHELL)
   (then issue the command to show active processes)
ps ax
   (Find the PID number of the process for ssh and issue the kill command, if the PID is 1234...)
kill 1234 

The SSHD configuration file should be reviewed for fitness to your security policy. In particular, the following items should be decided upon:

• The AllowUsers directive by default allows ALL active users to connect and execute PASE and system commands, even if they are limited users. Check the AllowUsers, AllowGroups, DenyUsers and DenyGroups directives to see what is good for you.

• The PermitRootLogin directive allows QSECOFR to login via SSH

Diagnosing Problems

You can invoke the sshd server manually to help diagnose problems.

• Shut down the SSHD server if it's already running ( ENDTCPSVR SERVER(*SSHD) )
• Open a QP2TERM command line shell (call QP2TERM)
• Invoke the sshd server with the '-d' parameter: /QOpenSys/QIBM/UserData/SC1/OpenSSH/openssh-3.8.1p1/sbin/sshd -d
• Try to connect from your ssh client.

NOTE: The sshd server will terminate as soon as this connection attempt is completed.

Security implications of using SSH on iSeries

http://archive.midrange.com/security400/200609/msg00048.html

External links

• PDF of Securing Communications with OpenSSH on IBM i5/OS (redp4163) at IBM Redpapers
• LPO 5733-SC1 -- IBM Portable Utilities for i
• How to set up SSH client on iSeries for password-less connections from midrange-l
• SSHSetup at YiPs Wiki