SSH authentication issue with OpenSSH private key

Question

I have an issue while trying to use the SSH command on my Kali Linux system (version 16.0-kali6-amd64, 2022-03-23). I'm attempting to authenticate using an OpenSSH private key.

I started by using the following command:

ssh -i id_rsa root@<ip>

However, this resulted in the following error:

Unable to negotiate with port 22: no matching host key type found. Their offer: ssh-rsa, ssh-dss

After some research, I tried the following command to address the issue:

ssh -oHostKeyAlgorithms=+ssh-dss -i id_rsa root@<ip>

But with this command, it prompted me for a password even though I intended to use the id_rsa key for authentication.

In the verbose output, I noticed the following messages:

• "No such directory for 'load_hostkeys'"
• "DSA host key found"
• "Get agent_identities: agent contains no identities, will attempt some key (explicitly)"
• "send_pubkey_test: no mutual signature algorithm"

The authentication process then attempted to use a password and provided a prompt.

I need assistance with using my OpenSSH private key for SSH authentication.

Answer 1

As mentioned by @dave_thompson, you can use additional argument when using ssh:

ssh -v -oHostKeyAlgorithms=+ssh-rsa username@ipaddress

or another alternative, if you often access server via ssh, you can create a file named config in folder .ssh, and then add this key inside config file:

Host [ipaddress]
    HostKeyAlgorithms=+ssh-rsa

This config file has same result as first way.

Answer 2

For Fedora release 38 (Thirty Eight):

Add one of code blocks to ~/.ssh/config:

Host ip.ip.ip.ip
    HostKeyAlgorithms +ssh-rsa
    PubkeyAcceptedAlgorithms +ssh-rsa

Host ip.ip.ip.ip
    HostKeyAlgorithms=+ssh-rsa
    PubkeyAcceptedAlgorithms=+ssh-rsa

All works.

Answer 3

I had to create ~/.ssh/config and add these lines to it.

Host 123.123.123.123
    KexAlgorithms=+diffie-hellman-group-exchange-sha1
Host 123.123.123.123
    HostKeyAlgorithms=+ssh-rsa

Answer 4

Just to specify the most concise way of adding more than one cipher in ~/.ssh/config:

Host oldserver
# solve the "host key" error on ancient server
HostKeyAlgorithms=+ssh-rsa,ssh-dss
# use key and eliminate password prompt on ancient server
PubkeyAcceptedAlgorithms=+ssh-rsa,ssh-dss

Answer 5

I was having problems connecting ubuntu with protostar vmbox. Accomplished it running this commad:

ssh -v -oHostKeyAlgorithms=+ssh-rsa -p 2222 [email protected]

With this network config in the vmbox:
Name: SSH
Protocol: TCP
Host IP: 127.0.0.1
Host Port: 2222
Guest IP: 10.0.2.15
Guest Port: 22