Topic: openssh
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SSH's "Host key verification failed" and "REMOTE HOST IDENTIFICATION HAS CHANGED" warnings
OpenSSH refuses to connect and prints 'Host key verification failed' or the larger 'WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!' banner when the server's key does not match what is stored in known_hosts. The article explains why a rebuilt server and an actual attack produce the identical message, and how to tell them apart before running ssh-keygen -R.
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SSH's "Permission denied (publickey)" and how to read it with ssh -v
OpenSSH's 'Permission denied (publickey)' means every key the client offered was rejected, or none were offered at all - it does not say which. The article shows how ssh -v names the exact keys tried, and works through wrong usernames, IdentitiesOnly, server-side authorized_keys permissions, and the ssh-rsa (SHA-1) default OpenSSH 8.8 disabled.
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Installing and hardening the built-in OpenSSH Server on Windows Server
Add-WindowsCapability installs the OpenSSH Server feature; sshd_config lives under %ProgramData%\ssh, an administrator's authorized keys must go in administrators_authorized_keys with a locked-down ACL or the server ignores them, and DefaultShell controls what an SSH session actually runs.
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