SSH Github Permission denied (publickey)

Question

I have been having trouble over the last few days trying to connect to a github account.

I have:

• Followed the guide to generate keys and add to github
• Followed the troubleshooting guide on Permission denied (My MD5 hash locally matches that of the one in my github account.)
• Tried verbose output when testing ssh connection

Here is the output for ssh -vT [email protected]

OpenSSH_7.5p1, OpenSSL 1.0.2l  25 May 2017
debug1: Reading configuration data /Users/[obfuscated]/.ssh/config
debug1: /Users/[obfuscated]/.ssh/config line 13: Applying options for *
debug1: /Users/[obfuscated]/.ssh/config line 24: Applying options for github.com
debug1: Reading configuration data /usr/local/etc/ssh/ssh_config
debug1: Connecting to github.com [192.30.253.112] port 22.
debug1: fd 5 clearing O_NONBLOCK
debug1: Connection established.
debug1: identity file /Users/[obfuscated]/.ssh/id_rsa type 1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/[obfuscated]/.ssh/id_rsa-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.5
debug1: Remote protocol version 2.0, remote software version libssh_0.7.0
debug1: no match: libssh_0.7.0
debug1: Authenticating to github.com:22 as 'git'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: [email protected]
debug1: kex: host key algorithm: ssh-rsa
debug1: kex: server->client cipher: [email protected] MAC: <implicit> compression: [email protected]
debug1: kex: client->server cipher: [email protected] MAC: <implicit> compression: [email protected]
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ssh-rsa SHA256:nThbg6kXUpJWGl7E1IGOCspRomTxdCARLviKw6E5SY8
The authenticity of host 'github.com (192.30.253.112)' can't be established.
RSA key fingerprint is SHA256:nThbg6kXUpJWGl7E1IGOCspRomTxdCARLviKw6E5SY8.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'github.com,192.30.253.112' (RSA) to the list of known hosts.
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey
debug1: No more authentication methods to try.
Permission denied (publickey).

Something interesting here I have noticed is that I dont have debug1: Offering RSA public key: /Users/you/.ssh/id_rsa or debug1: Trying private key: /Users/you/.ssh/id_rsa in my debug. Almost as if that part is being skipped. I do have debug1: identity file /Users/[obfuscated]/.ssh/id_rsa type 1 though, so it seems like it has found the file.

Here is my .ssh/config:

Host localhost
  ControlMaster no

# default for all hosts
Host *
     ConnectTimeout 30
     ServerAliveInterval 30
     ControlMaster auto
     ControlPersist 60s
     HashKnownHosts yes
     GSSAPIAuthentication no
     IdentitiesOnly yes
     Compression yes

# github user
Host github.com
     HostName github.com
     User git
     PreferredAuthentications publicKey
     IdentityFile ~/.ssh/id_rsa

# the local raspberry pi dns ad block server
Host pi
     HostName [obfuscated]
     User pi
     IdentityFile ~/.ssh/pi_rsa

Permissions for ssh files

 8 -rw-r--r--   1 [obfuscated]  staff   802B Sep  9 21:45 config
 8 -rw-------   1 [obfuscated]  staff   3.2K Sep  9 21:16 id_rsa
 8 -rw-r--r--   1 [obfuscated]  staff   747B Sep  9 21:16 id_rsa.pub
 8 -rw-r--r--   1 [obfuscated]  staff   885B Sep  9 21:37 known_hosts
 8 -rw-------   1 [obfuscated]  staff   1.7K Oct 21  2016 pi_rsa
 8 -rw-r--r--   1 [obfuscated]  staff   405B Oct 21  2016 pi_rsa.pub

Answer 1

Short answer: I had a typo in my .ssh/config.

PreferredAuthentications publicKey

should have had a lower case k

PreferredAuthentications publickey

How I discovered the issue:

On most systems the default private keys (~/.ssh/id_rsa, ~/.ssh/id_dsa and ~/.ssh/identity) are automatically added to the SSH authentication agent. You shouldn't need to run ssh-add path/to/key unless you override the file name when you generate a key.

By knowing this, I removed my custom config for github.com so that the SSH authentication agent would use my key by default.

This allowed me to connect. I then added back one line at a time until I found that PreferredAuthentications publicKey was not working. I googled it to check the syntax and found the issue was the upper case K.