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SSH public key authentication on OpenVMS

05-04-2018 | Remy van Elst | Text only version of this article


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(You can read all my OpenVMS articles by clicking the picture above)

My OpenVMS adventure continues, after my rabbit hole of folder removal, this time I actually get public key authentication working with OpenSSH so that I don't have to type my password to login.

There is a bit of documentation from HP to set up SSH key authentication but that misses one important little thing. That thing took me a few days to figure out.

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Client public key authentication

On the HPe website there is extensive documentation on both the SSH server setup as well as the client setup on OpenVMS. On the DECUServe system I'm not an administrative user so this article will only cover the client part. It assumes a set up and working SSH server.

SSH public key authentication allows you to login to an SSH server without specifying a password. It is more secure since passwords can easily be brute forced. An SSH key can be securely on a HSM so that the private part never is exposed and SSH keys allow for key forwarding, that means you can use the key from your laptop to login to other servers and then logon further to machines behind there without placing your private key on the intermidiate machines.

Overall SSH keys are considered to be best practice instead of passwords.

Since I access the DECUServe system via SSH with a password I was wondering if OpenVMS would support key authentication and according to the documentation it should just be simple. Place the public key and configure it to allow login.

But sadly that was not all.

Creating the files and folders.

First create an [SSH2] folder in your homedir:

 $ CREATE /DIRECTORY [.SSH2]
 $ DIR [.SSH2]
%DIRECT-W-NOFILES, no files found

Create the configuration file in which we explicitly allow public key authentication next to password login:

 $ EVE [.SSH2]SSH2_CONFIG 

Place the following line in there:

AllowedAuthentications publickey, password

Directly underneath that the EVE editor will show this:

[End of file]

 Buffer: SSH2_CONFIG.                                                                                                                                                     | Write | Insert | Forward

1 line read from file EISNER$DRA3:[DECUSERVE_USER.EXAMPLE.SSH2]SSH2_CONFIG.;2

Save the file with CTRL+Z. As you can see via the ;2 file version number I was messing around. Did I mention how awesome it is that OpenVMS has file versioning built in the filesystem?

On linux and other systems that use OpenSSH, you would create ~/.ssh/authorized_keys and place your key(s) in there like so:

ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQCq1vxYvJNBZMtrufZD0ivHXrt0A+WhslMcWeQTU2du2jznw64ScrxN+EYXVGg3JKu8N/QK/0VrtsxITFthHJQP0FkC0J8GnWeT3x2y0N38P+H3B/h1rh9DBY/GTUlXY9Q0MKAOEdTjSecK11Nd5183Xcygnv5xAxLqzqmnllumAE1Wd/B0NoKrcSy51hERn0kKTR9hIw8FTOUNPAwTgsMJ+A10aJtqjlk4OrOd1KOHi1jWNTc5wcW6xgWzMksdw++fBBPcJN9Bgihxz9kSwdpkcIYlBkIZZEwZtTvNy7K2nKw94omWmdr0ZlqsNwfOihyQpo4wtusjakTmM4GA+bH3 remy@gateway

On OpenVMS, you create a file named AUTHORIZATION and in there you specify filenames of public keys, like KEY EXAMPLE-HOSTNAME.PUB where EXAMPLE-HOSTNAME.PUB is the file name with the format $USER-$HOST.PUB.

Use EVE to create this AUTHORIZATION. file and add the filename of your public key file:

 $ EVE [.SSH2]AUTHORIZATION

My key example:

KEY REMY-GATEWAY.PUB

Note, do not add the key here like you might be used to on linux, just make up a filename, prefixed with KEY. Next create the actual key file:

 $ EVE [.SSH2]REMY-GATEWAY.PUB

Paste your public key and save with CTRL+Z.

The documentation states that the public key file requires specific permission. On linux I'm used to setting permissions on the authorized_keys file and the private key material, but this will be comparable I guess:

SET FILE /PROTECTION=(S:WRED,O:WRED,G:RE,W:R) [.SSH2]REMY-GATEWAY.PUB

You can check the current permissions with the SHOW SECURITY command:

 $ SHOW SECURITY [.SSH2]REMY-GATEWAY.PUB

EISNER$DRA3:[DECUSERVE_USER.EXAMPLE.SSH2]REMY-GATEWAY.PUB;2 object of class FILE
     Owner: [EXAMPLE]
     Protection: (System: RWED, Owner: RWED, Group: RE, World: R)
     Access Control List: <empty>

By default, or at least on DECUServe my files get the following permissions:

     Protection: (System: RWED, Owner: RWED, Group, World)

Now you should be all set to go. Login specifically disabling password login using your key:

$ ssh -oHostKeyAlgorithms=+ssh-dss -o "PasswordAuthentication no"  EXAMPLE@eisner.decus.org

Output:

The authenticity of host 'eisner.decus.org (104.207.199.162)' can't be established.
DSA key fingerprint is SHA256:S0vOOBec5QvjeC1aLvnSccBewSgOvsF2s97KGaY1pnE.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'eisner.decus.org,104.207.199.162' (DSA) to the list of known hosts.

                                N O T I C E

This is Encompasserve.  Access is for subscribed individuals only.

 o  By logging into the system you agree to abide by the Encompasserve
    Canons of Conduct.

 o  Source code or any other information posted on this system is not
    warranted in any way.  YOU USE IT AT YOUR OWN RISK.

 o  If you submit source code to or post information on this system, you
    must allow its unrestricted use.  You must have the right to grant
    such permission.

 o  Refer to the Encompasserve Canons of Conduct, posted in the
    DECUServe_Information conference topic 4.3, for further guidance.

 o  Report problems in DECUServe_Forum.


For information about Encompasserve please login under -> Username INFORMATION
To subscribe to Encompasserve       please login under -> Username REGISTRATION
To report any form of a problem     please login under -> Username PROBLEMS
To renew an Expired account         please login under -> Username REGISTRATION

Permission denied (publickey,password).

Err, what? We followed the documentation to the letter?

Why does it not work?

This problem took me a few days to resolve. As I have no access to logging on the OpenVMS system and no knowledge of how to view said logging, I was left to trial and error.

To save you time and trouble, it appears that the key file was not in the correct format for OpenVMS. We pasted the OpenSSH key format in the key file but there is another format. I found this on a USENET newsgroup, you know you're far in the exotic corners of the internet when you're searching comp.os.vms. But hey, it helped me solve this issue.

OpenVMS uses IEFT SECSH (Tectia) format keys. There is an IETF document describing the format and a document on the SSH key subsystem if you want to know more.

The DECUServe system does not have the SSH-KEYGEN OpenVMS program installed or at least I got an error when trying to execute it. Otherwise I would have tried to create a key there and compare the files and permissions with my own file.

OpenSSH uses, suprisingly, openssh format public keys. The ones you know and probably 99% of the regular internet uses. But as always there are special snowflakes and it seems this is one of them. Googling around also gave lot's of hits for IBM and z/OS.

Using ssh-keygen (on linux) we can convert a private key to this format with the -e option. From the man page:

 -e Extract/convert from OpenSSH private key file to SECSH public key format 

In my case:

$ ssh-keygen -e -f ~/.ssh/id_rsa

Output:

---- BEGIN SSH2 PUBLIC KEY ----
Comment: "2048-bit RSA, converted by remy@gateway from OpenSSH"
AAAAB3NzaC1yc2EAAAADAQABAAABAQCq1vxYvJNBZMtrufZD0ivHXrt0A+WhslMcWeQTU2
du2jznw64ScrxN+EYXVGg3JKu8N/QK/0VrtsxITFthHJQP0FkC0J8GnWeT3x2y0N38P+H3
B/h1rh9DBY/GTUlXY9Q0MKAOEdTjSecK11Nd5183Xcygnv5xAxLqzqmnllumAE1Wd/B0No
KrcSy51hERn0kKTR9hIw8FTOUNPAwTgsMJ+A10aJtqjlk4OrOd1KOHi1jWNTc5wcW6xgWz
Mksdw++fBBPcJN9Bgihxz9kSwdpkcIYlBkIZZEwZtTvNy7K2nKw94omWmdr0ZlqsNwfOih
yQpo4wtusjakTmM4GA+bH3
---- END SSH2 PUBLIC KEY ----

Use the editor to update your KEY file on OpenVMS, in my case [.SSH]REMY-GATEWAY.PUB. Save with CTRL+Z and retry:

$ ssh -oHostKeyAlgorithms=+ssh-dss -o "PasswordAuthentication no" -i .ssh/id_rsa EXAMPLE@eisner.decus.org

Output:

                                N O T I C E

This is Encompasserve.  Access is for subscribed individuals only.

 o  By logging into the system you agree to abide by the Encompasserve
    Canons of Conduct.

 o  Source code or any other information posted on this system is not
    warranted in any way.  YOU USE IT AT YOUR OWN RISK.

 o  If you submit source code to or post information on this system, you
    must allow its unrestricted use.  You must have the right to grant
    such permission.

 o  Refer to the Encompasserve Canons of Conduct, posted in the
    DECUServe_Information conference topic 4.3, for further guidance.

 o  Report problems in DECUServe_Forum.


For information about Encompasserve please login under -> Username INFORMATION
To subscribe to Encompasserve       please login under -> Username REGISTRATION
To report any form of a problem     please login under -> Username PROBLEMS
To renew an Expired account         please login under -> Username REGISTRATION

    Last interactive login on Thursday,  5-APR-2018 14:10:22.71


%DCL-S-SPAWNED, process EXAMPLE_62002 spawned
  User [EXAMPLE] has 132 blocks used, 9868 available,
  of 10000 authorized and permitted overdraft of 0 blocks on DISK_USER
 $
Subprocess EXAMPLE_62002 has completed
 $

Yay!

Conclusion

I learned a lot, again. I notice that filesystem actions like editing and permissions are a bit easier for me since I'm beginning to grasp the concepts and commands. To summarize:

  • OpenVMS supports public key authentication
  • It's almost the same as with OpenSSH on Linux
  • Define your public key in an AUTHORIZATION file and place the key on the system
  • Make sure it is the correct key format
  • Set the correct permissions
  • ???
  • PROFIT!!

One more thing, LOGOUT of OpenVMS

In an earlier article I wrote that I was unable to logout on OpenVMS since exit and CTRL+D not exited the SSH session. I stopped my sessions using either ~. or by closing the window.

In the same comp.os.vms I found the LOG command. The help says:

 $ HELP LOG

[...]
LOGOUT

     Terminates an interactive terminal session.

     Format

       LOGOUT

So, now I can type 'LOG' on the prompt and exit OpenVMS.


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