I already checked here: Trying to do ssh authentication with key files: server refused our key

and I did all these:


  • generated key(s) via ssh-gen in a Linux client.
    • added the public key to the server via ssh-copy

now I don't see any error message, here's ssh -vvv:

Could it be that there's an order to the authentication process, but the server first tries to verify password, instead of trying out the publickey?

Original post: what I tried so far:

  • generated key(s) via puttygen (v.2015-12-03) in the windows client:

    • 2048 bits, and tried also key-pair with 1024 bits
  • copied "openssh public key" in 1 line format from puttygen,

    • the line that looks like:

      ssh-rsa xxxx... ==
    • pasted it to the ubuntu server to ~/.ssh/authorized_keys

    • one line for the 2048 bit key, additional line for the 1024 bit key

  • I changed the file permissions like so:

    chmod 700 ~/.ssh
    chmod 600 authorized_keys
    chmod 700 ~
    chown -R $USER.$USER ~/
  • putty session settings:

    • 'connection' > 'data' > 'username' > myuser

    • 'connection' > 'ssh' > 'auth' > the PPK file

  • tried with both 2048 bit and 1024 keys (with their respective public keys)

  • tried also from localhost (ssh -i .ssh/mykey myuser@localhost) – got the same /var/log/auth error:

    Failed publickey for (myuser) from ::1 port 50087
  • increased log level of /etc/sshd_config: LogLevel VERBOSE (is there higher value?) on the server, and restarted. /var/log/auth.log now gives:

    **Failed publickey for** myuser from xx.xx.xx.xx port xx: RSA xx:xx:xx...


  • tried to connect from:
    • from windows (putty 2015-12-3, key is PPK)
    • from linux/mint 17 (via ssh, openssh key)
  • server: Ubuntu 14.04.2 LTS
  • keys generated by puttygen on windows (v.2015-12-03)
  • also tried with "kitty" (a putty fork)
  • ssh with password - works. always.

tail -f /var/log/auth.log isn't showing anything for failed logins, only for successful and for logouts.

Can it be cured?

is there another way to diagnose the problem?


Q. What is a "data" connection? Why didn't you use "ssh" in both cases?

A. it's just the section's name in putty config.

Q. cat /etc/ssh/sshd_config|grep -i author

A. AuthorizedKeysFile ~/.ssh/authorized_keys

Q. ls -lZ .ssh (on the server)

drwx------ 2 myuser myuser ? 4096 Dec  5 12:28 .   <---- the .ssh dir
-rw-r--r-- 1 myuser myuser ?  666 Dec  5 12:29 known_hosts
-rw------- 1 myuser myuser ? 1671 Dec  3 12:07 mykey.ssh
-rw------- 1 myuser myuser ?  608 Dec  3 11:47 authorized_keys

  • Should we assume you are connecting from a Windows machine? Can you connect to your Ubuntu machine from another Linux installation? How about ssh localhost from the Ubuntu? Where did the rsa key come from? How was it generated? Did you add it to the host or client machine? What machine was each command you show run on? What do the putty > connection lines mean? Are those options in the putty GUI? What is a "data" connection? Why didn't you use "ssh" in both cases? Please edit your question and clarify.
    – terdon
    Dec 3, 2015 at 10:58
  • increase debug level on the server and restart. Or run server in debug mode and follow the messages. Some publickey failures are not logged
    – Jakuje
    Dec 3, 2015 at 13:58
  • @terdon - i clarified the details you asked for, changed the log level, and ran other tests Dec 5, 2015 at 10:46
  • I have come across a similar problem with PuTTY, and it happens on some computers but not others. Did your public key have the same format as the one in the linked question: a "BEGIN" line, a "comment" line, 4 lines of ASCII with the first line beginning ssh-rsa and the last line ending user@computer? Could you clarify what you mean by "copied "openssh public key" in 1 line format from puttygen": did you copy only the line beginning with ssh-rsa, or did you copy all lines of ASCII, removing the line breaks so that it fit onto one line? Dec 16, 2015 at 22:53
  • 1
    Please increase the verbosity of the OpenSSH client (ssh -v [OPTIONS...] user@host – add more v's to increase verbosity to a suitable level) and include the output in your question. My way to debug issues from the server side is to run the OpenSSH server in debug mode, i. e. without detaching from the terminal: sudo sshd -d (add more d's for more verbosity). Of course you need to stop the SSH service first (sudo service ssh stop). Maybe you can provide an excerpt of that output too. Dec 17, 2015 at 11:04

2 Answers 2


A less error-prone way of converting public key formats than manually removing the headers and line-breaks is using ssh-keygen like this:

ssh-keygen -i -f publickeywithheaders.pub

It should output what can be appended to the authorized_keys file.

  • You are correct, but this cannot be done in PuTTY, and to do it in Windows at all requires installation of some kind of unix/linux environment tools (other than PuTTY), such as Cygwin/X. It can be done in the OP's linux/mint 17 installation though, which was what I was about to suggest. The private key can then be copied to the Windows machine, where puttygen can import the private key and save it in PuTTY PPK format, for use with PuTTY. Dec 23, 2015 at 10:21
  • In my example, ssh-keygen is not used to generate the key but to convert it to OpenSSH's native format.
    – Black
    Dec 23, 2015 at 12:28
  • Yes sorry my mistake, I looked at your answer a little too quickly. That looks like a handy technique Dec 23, 2015 at 18:44

I have come across this before in PuTTY, where the public key is written like this (like in your linked question):

Comment: "user@computer"
ssh-rsa blah1blah2blah3blah4

As you know, it needs to be one line, the one starting with ssh-rsa. That is, delete the "BEGIN" line, the "comment" line, and the "END" line.

However, I am not sure if you did this:

ssh-rsa blah1blah2blah3blah4

What you need to do is this:

ssh-rsa blah1blah2blah3blah4blah5blah6blah7blah8blah9blah10blah11blah12blah13blah14=user@computer

(i.e. copy all four lines containing the key AND delete the line breaks)

  • i copied from puttygen the one-line version of the ssh-rsa, which looks exactly as you suggested Dec 23, 2015 at 8:41

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