Paramiko AuthenticationException issue

Question

I am having a problem connecting to a device with a Paramiko (version 1.7.6-2) ssh client:

$ python
Python 2.6.5 (r265:79063, Apr 16 2010, 13:09:56) 
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import paramiko
>>> ssh = paramiko.SSHClient()
>>> ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
>>> ssh.connect("123.0.0.1", username="root", password=None)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/pymodules/python2.6/paramiko/client.py", line 327, in connect
    self._auth(username, password, pkey, key_filenames, allow_agent, look_for_keys)
  File "/usr/lib/pymodules/python2.6/paramiko/client.py", line 481, in _auth
    raise saved_exception
paramiko.AuthenticationException: Authentication failed.
>>> 

When I use ssh from the command line, it works fine:

ssh [email protected]


BusyBox v1.12.1 (2010-11-03 13:18:46 EDT) built-in shell (ash)
Enter 'help' for a list of built-in commands.

# 

Anyone seen this before?

Edit 1

Here is the verbose output of the ssh command:

:~$ ssh -v [email protected]
OpenSSH_5.3p1 Debian-3ubuntu4, OpenSSL 0.9.8k 25 Mar 2009
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to 123.0.0.1 [123.0.0.1] port 22.
debug1: Connection established.
debug1: identity file /home/waffleman/.ssh/identity type -1
debug1: identity file /home/waffleman/.ssh/id_rsa type -1
debug1: identity file /home/waffleman/.ssh/id_dsa type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.1
debug1: match: OpenSSH_5.1 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.3p1 Debian-3ubuntu4
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: Host '123.0.0.1' is known and matches the RSA host key.
debug1: Found key in /home/waffleman/.ssh/known_hosts:3
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentication succeeded (none).
debug1: channel 0: new [client-session]
debug1: Requesting [email protected]
debug1: Entering interactive session.
debug1: Sending environment.
debug1: Sending env LANG = en_US.utf8

Edit 2 Here is the python output with debug output:

Python 2.6.5 (r265:79063, Apr 16 2010, 13:09:56) 
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import paramiko, os
>>> paramiko.common.logging.basicConfig(level=paramiko.common.DEBUG)
>>> ssh = paramiko.SSHClient()
>>> ssh.load_system_host_keys()
>>> ssh.load_host_keys(os.path.expanduser('~/.ssh/known_hosts'))
>>> ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
>>> ssh.connect("123.0.0.1", username='root', password=None)
DEBUG:paramiko.transport:starting thread (client mode): 0x928756cL
INFO:paramiko.transport:Connected (version 2.0, client OpenSSH_5.1)
DEBUG:paramiko.transport:kex algos:['diffie-hellman-group-exchange-sha256', 'diffie-hellman-group-exchange-sha1', 'diffie-hellman-group14-sha1', 'diffie-hellman-group1-sha1'] server key:['ssh-rsa', 'ssh-dss'] client encrypt:['aes128-cbc', '3des-cbc', 'blowfish-cbc', 'cast128-cbc', 'arcfour128', 'arcfour256', 'arcfour', 'aes192-cbc', 'aes256-cbc', '[email protected]', 'aes128-ctr', 'aes192-ctr', 'aes256-ctr'] server encrypt:['aes128-cbc', '3des-cbc', 'blowfish-cbc', 'cast128-cbc', 'arcfour128', 'arcfour256', 'arcfour', 'aes192-cbc', 'aes256-cbc', '[email protected]', 'aes128-ctr', 'aes192-ctr', 'aes256-ctr'] client mac:['hmac-md5', 'hmac-sha1', '[email protected]', 'hmac-ripemd160', '[email protected]', 'hmac-sha1-96', 'hmac-md5-96'] server mac:['hmac-md5', 'hmac-sha1', '[email protected]', 'hmac-ripemd160', '[email protected]', 'hmac-sha1-96', 'hmac-md5-96'] client compress:['none', '[email protected]'] server compress:['none', '[email protected]'] client lang:[''] server lang:[''] kex follows?False
DEBUG:paramiko.transport:Ciphers agreed: local=aes128-ctr, remote=aes128-ctr
DEBUG:paramiko.transport:using kex diffie-hellman-group1-sha1; server key type ssh-rsa; cipher: local aes128-ctr, remote aes128-ctr; mac: local hmac-sha1, remote hmac-sha1; compression: local none, remote none
DEBUG:paramiko.transport:Switch to new keys ...
DEBUG:paramiko.transport:Trying discovered key b945197b1de1207d9aa0663f01888c3c in /home/waffleman/.ssh/id_rsa
DEBUG:paramiko.transport:userauth is OK
INFO:paramiko.transport:Authentication (publickey) failed.
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/pymodules/python2.6/paramiko/client.py", line 327, in connect
    self._auth(username, password, pkey, key_filenames, allow_agent, look_for_keys)
  File "/usr/lib/pymodules/python2.6/paramiko/client.py", line 481, in _auth
    raise saved_exception
paramiko.AuthenticationException: Authentication failed.
>>> 

Answer 1

It's really a old and remote issue, but I just got the same error and I think It'll be helpful to list the following info:

1. I'm using paramiko 2.9.1 and python>=3.6, make sure your paramiko>=2.9.0
2. cmd ssh <hostname> works fine
3. Code below get error: AuthenticationException: Authentication failed.

import paramiko
client = paramiko.SSHClient()
client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
session = client.connect("<hostname>")

From here https://github.com/paramiko/paramiko/issues/1984, I know this is a bug related to auth algorithms.

You'll need to add a disabled_algorithms param in connect(), see docs here: https://www.paramiko.org/changelog.html#2.9.0

But the changelog of 2.9.0 has a typo for disabled_algorithms, it should be:

client.connect("<hostname>", disabled_algorithms={'pubkeys': ['rsa-sha2-256', 'rsa-sha2-512']})

instead of:

client.connect("<hostname>", disabled_algorithms={'keys': ['rsa-sha2-256', 'rsa-sha2-512']})

Finally, all goes well.

Ps: Just got error Unable to agree on a pubkey algorithm for signing a 'ssh-rsa' key! for other hosts, may be downgrade paramiko below 2.9.0 is a better way.

Answer 2

Make sure that the permissions on the public and private key files (and possibly the containing folder) are set to very restrictive (i.e. chmod 600 id_rsa). It turns out this is required (by the Operating System?) to use the files as ssh keys. Found this out from my helpful colleague :) Also make sure that you are using the correct username for the given ssh key.