How to know if I can use ssh keypairs?

Question

After running successfully, my build script attempts to copy the final binary onto my FTP server using the scp command. Since the build takes a while, I don't want to be prompted for my password every time, so I tried to set up an SSH-keypair.

[wbarlow@build-machine]$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/wbarlow/.ssh/id_rsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/wbarlow/.ssh/id_rsa.
Your public key has been saved in /home/wbarlow/.ssh/id_rsa.pub.
The key fingerprint is:
7f:b9:c7:a8:1b:77:ce:f8:b6:2a:e3:da:30:68:72:b7 wbarlow@build-machine

[wbarlow@build-machine]$ ssh-copy-id wbarlow@ftp-server
wbarlow@ftp-server's password: 
Now try logging into the machine, with "ssh 'wbarlow@ftp-server'", and check in:

  ~/.ssh/authorized_keys

to make sure we haven't added extra keys that you weren't expecting.

Then I tried to sign into my ftp-server, but I was still prompted for a password. I confirmed that the freshly created key was present.

[wbarlow@build-machine]$ ssh wbarlow@ftp-server
wbarlow@ftp-server's password: 

[wbarlow@ftp-server]$ cat ~/.ssh/authorized_keys
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDGUbr4vUeiY7D6sSrsHm469QAqCClchL
7h/HZ7TAc+1F2KsTTF078OSINqzz8NpKJqhlEusLn644PzYn9LmGTIc7IsMG9s+B2n4bZX
9Ypb0VqLSqTgfE2I0j84+SfAQ6MvGJQ0NupIXxXbaMLDlNq1cetnR8NeN+9JeBq4sI8p/a
ijFVARQ7/XSKwQQN30Nl6flTEM1CTDECJs5YsPOu3P54mF6PG2mBdFra6+VQfAZ6fboq9O
d24VNHLYVtUdK5RpWgx8agUalov0xq/3m2VeC5arrYpCVH1rGx6EMxoQS25kk7t9mzBUCj
ulXGWQX2DPR/Em0OIfvVfe/l4xtFfH wbarlow@build-machine

I am able to use the public key to authenticate with other machines (namely, my Git repository host), so I don't think that the problem is on the client-side.

So -- how can I check that the FTP server is configured to accept authorized keys, and what sort of keys is it configured to accept? How can I check that the keys are being stored in the expected place (my home directory on ftp-server is /var/ftp/wbarlow/, but I've also tried copying the .ssh folder from there to /home/wbarlow/.)?

---

My .ssh directory is mode 700, and my authorized_keys file is mode 600. I've also tried using 755 for the .ssh directory.

---

I found my /etc/ssh/sshd_config file on the ftp-server. I won't post the whole thing, but it does have the following lines:

RSAAuthentication yes
PubkeyAuthentication yes
AuthorizedKeysFile      .ssh/authorized_keys

# To disable tunneled clear text passwords, change to no here!
#PasswordAuthentication yes
#PermitEmptyPasswords no
PasswordAuthentication yes

# Change to no to disable s/key passwords
#ChallengeResponseAuthentication yes
ChallengeResponseAuthentication no

As far as I can tell from the documentation, I think these lines are set correctly for what I want to do (s/key is something unrelated to ssh keypairs, right?).

---

Below is the verbose output while connecting.

[wbarlow@build-machine]:~$ ssh -v wbarlow@ftp-server
OpenSSH_6.1p1 Debian-4, OpenSSL 1.0.1c 10 May 2012
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to ftp-server [(ip hidden)] port 22.
debug1: Connection established.
debug1: identity file /home/wbarlow/.ssh/id_rsa type 1
debug1: Checking blacklist file /usr/share/ssh/blacklist.RSA-2048
debug1: Checking blacklist file /etc/ssh/blacklist.RSA-2048
debug1: identity file /home/wbarlow/.ssh/id_rsa-cert type -1
debug1: identity file /home/wbarlow/.ssh/id_dsa type -1
debug1: identity file /home/wbarlow/.ssh/id_dsa-cert type -1
debug1: identity file /home/wbarlow/.ssh/id_ecdsa type -1
debug1: identity file /home/wbarlow/.ssh/id_ecdsa-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.1
debug1: match: OpenSSH_5.1 pat OpenSSH_5*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.1p1 Debian-4
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-md5 none
debug1: kex: client->server aes128-ctr hmac-md5 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Server host key: RSA [SNIP]
debug1: Host 'ftp-server' is known and matches the RSA host key.
debug1: Found key in /home/wbarlow/.ssh/known_hosts:1
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,gssapi-with-mic,password
debug1: Next authentication method: gssapi-with-mic
debug1: Unspecified GSS failure.  Minor code may provide more information
Cannot determine realm for numeric host address

debug1: Unspecified GSS failure.  Minor code may provide more information
Cannot determine realm for numeric host address

debug1: Unspecified GSS failure.  Minor code may provide more information


debug1: Unspecified GSS failure.  Minor code may provide more information
Cannot determine realm for numeric host address

debug1: Next authentication method: publickey
debug1: Offering RSA public key: /home/wbarlow/.ssh/id_rsa
debug1: Authentications that can continue: publickey,gssapi-with-mic,password
debug1: Trying private key: /home/wbarlow/.ssh/id_dsa
debug1: Trying private key: /home/wbarlow/.ssh/id_ecdsa
debug1: Next authentication method: password
wbarlow@ftp-server's password: 

Answer 1

Config settings for the SSH server are often in /etc/ssh/sshd_config but the first thing I would check is the location and the permissions of the public key and its parent directory that you copied to the server.
Noting that correct permissions of authorized_keys on the remote are critical for ssh to work - and hence why we use ssh-copy-id and not simply copying the public key to the remote.
To understand this it may be useful to breakdown what the ssh-copy-id does.

First thing it does is secure copy id_rsa.pub over to the target server i.e.

scp -P port $HOME/.ssh/id_rsa.pub username@ipaddress:destination_path

and place in ~/.ssh/ of the remote machine.

it will also rename id_rsa.pub to authorized_keys so you end up with

$ ~/.ssh/authorized_keys

on remote machine.
It also sets the permissions which is critical i.e. authorized_keys file must be no less secure than

-rw------- 1 wbarlow wbarlow  802 Nov 25 13:54 authorized_keys

and .ssh directory cannot be less secure than 755 e.g.

drwx------ 2 wbarlow wbarlow  4096 Jul 29 00:30 .ssh

I tend to use the command

ssh-copy-id -i ~/.ssh/id_rsa.pub remote_user@remoteIP

that way the specific key I want gets onto the remote, but I don't think that would be your problem,as I suspect ssh will check all available private keys on your local machine when trying to establish a connection.

Also, as always, make sure to check the basic permissions of the containing folders ($HOME) so that other users/programs have appropriate file privileges .

Answer 2

Config settings for the SSH server are often in /etc/ssh/sshd_config but the first thing I would check is the location and the permissions of the public key and its parent directory that you copied to the server.

/etc/ssh/sshd_config should be like this . sshd service need to be stopped and started again

PermitRootLogin yes

RSAAuthentication yes
PubkeyAuthentication yes
AuthorizedKeysFile      .ssh/authorized_keys