Roman Cheplyaka

Fixing Permission denied (publickey). after an SSH upgrade

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This weekend I upgraded my laptop from Fedora 22 to 23. Today, when I tried to push to github, I suddenly got

% git push     
Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

To debug this, I ran (according to these instructions)

% ssh -vT git@github.com
OpenSSH_7.1p1, OpenSSL 1.0.2e-fips 3 Dec 2015
debug1: Reading configuration data /home/feuerbach/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 56: Applying options for *
debug1: Connecting to github.com [192.30.252.129] port 22.
debug1: Connection established.
debug1: identity file /home/feuerbach/.ssh/id_rsa type 1
debug1: key_load_public: No such file or directory
debug1: identity file /home/feuerbach/.ssh/id_rsa-cert type -1
debug1: identity file /home/feuerbach/.ssh/id_dsa type 2
debug1: key_load_public: No such file or directory
debug1: identity file /home/feuerbach/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/feuerbach/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/feuerbach/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/feuerbach/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/feuerbach/.ssh/id_ed25519-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.1
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: server->client chacha20-poly1305@openssh.com <implicit> none
debug1: kex: client->server chacha20-poly1305@openssh.com <implicit> none
debug1: kex: curve25519-sha256@libssh.org need=64 dh_need=64
debug1: kex: curve25519-sha256@libssh.org need=64 dh_need=64
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ssh-rsa SHA256:nThbg6kXUpJWGl7E1IGOCspRomTxdCARLviKw6E5SY8
debug1: Host 'github.com' is known and matches the RSA host key.
debug1: Found key in /home/feuerbach/.ssh/known_hosts:19
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
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /home/feuerbach/.ssh/id_rsa
debug1: Authentications that can continue: publickey
debug1: Skipping ssh-dss key /home/feuerbach/.ssh/id_dsa for not in PubkeyAcceptedKeyTypes
debug1: Trying private key: /home/feuerbach/.ssh/id_ecdsa
debug1: Trying private key: /home/feuerbach/.ssh/id_ed25519
debug1: No more authentication methods to try.
Permission denied (publickey).

The important line is this one

debug1: Skipping ssh-dss key /home/feuerbach/.ssh/id_dsa for not in PubkeyAcceptedKeyTypes

It turns out that Fedora 23 ships with OpenSSH 7.1p1 which has disabled DSS (aka DSA) keys by default.

A short term solution is to add

Host *
PubkeyAcceptedKeyTypes=+ssh-dss

to ~/.ssh/config. A long-term solution is to replace the DSS keys with, say, RSA keys.