After a recent macOS upgrade, some ssh access was strangely blocked. I turned on verbose logs to check the problem.
$ ssh -vvvv my-host debug3: order_hostkeyalgs: prefer hostkeyalgs: rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,rsa-sha2-512,rsa-sha2-256 debug3: send packet: type 20 debug1: SSH2_MSG_KEXINIT sent debug3: receive packet: type 20 debug1: SSH2_MSG_KEXINIT received debug2: local client KEXINIT proposal debug2: KEX algorithms: sntrup761x25519-sha512@openssh.com,curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,ext-info-c debug2: host key algorithms: rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,rsa-sha2-512,rsa-sha2-256,ssh-ed25519-cert-v01@openssh.com,ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ssh-ed25519,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521 debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com debug2: MACs ctos: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1 debug2: MACs stoc: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1 debug2: compression ctos: none,zlib@openssh.com,zlib debug2: compression stoc: none,zlib@openssh.com,zlib debug2: languages ctos: debug2: languages stoc: debug2: first_kex_follows 0 debug2: reserved 0 debug2: peer server KEXINIT proposal debug2: KEX algorithms: curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1 debug2: host key algorithms: ssh-rsa debug2: ciphers ctos: aes128-gcm@openssh.com,chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr debug2: ciphers stoc: aes128-gcm@openssh.com,chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr debug2: MACs ctos: hmac-sha2-256-etm@openssh.com,hmac-sha2-256,hmac-sha1,hmac-sha1-96 debug2: MACs stoc: hmac-sha2-256-etm@openssh.com,hmac-sha2-256,hmac-sha1,hmac-sha1-96 debug2: compression ctos: none debug2: compression stoc: none debug2: languages ctos: debug2: languages stoc: debug2: first_kex_follows 0 debug2: reserved 0 debug1: kex: algorithm: curve25519-sha256@libssh.org debug1: kex: host key algorithm: (no match) Unable to negotiate with UNKNOWN port 65535: no matching host key type found. Their offer: ssh-rsa
According to the logs above. This probably means we don't support host key types like ssh-rsa anymore... emm, okay.
But I can't change the server, I have to make my local support that.
Edit file $HOME/.ssh/config, and add a new line after Host my-host.
Host my-host
HostName google.com
# other configs
HostKeyAlgorithms +ssh-rsa
After the configuration is changed, the effect of the new log is as follows:
... debug3: order_hostkeyalgs: prefer hostkeyalgs: rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,rsa-sha2-512,rsa-sha2-256,ssh-rsa ... debug1: kex: algorithm: curve25519-sha256@libssh.org debug1: kex: host key algorithm: ssh-rsa ... debug3: remaining preferred: keyboard-interactive,password debug3: authmethod_is_enabled publickey debug1: Next authentication method: publickey debug1: Offering public key: $HOME/.ssh/id_rsa RSA SHA256:XXXX explicit debug1: send_pubkey_test: no mutual signature algorithm debug2: we did not send a packet, disable method debug3: authmethod_lookup password
Although the host authentication is passed, the password is still required. Local key pairs didn't accepted due to "no mutual signature algorithm". Continue to edit the $HOME/.ssh/config file, and add a line after Host my-host as follows:
Host my-host
HostName google.com
# other configs
HostKeyAlgorithms +ssh-rsa
PubkeyAcceptedKeyTypes +ssh-rsa
Finally it seems to work.
