sshd: Suppress host key loading error when using a PKCS#11 based HostKey#664
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ifranzki wants to merge 1 commit into
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sshd: Suppress host key loading error when using a PKCS#11 based HostKey#664ifranzki wants to merge 1 commit into
ifranzki wants to merge 1 commit into
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When using a PKCS#11 based HostKey then the private key is loaded via the SSH agent using the HostKeyAgent setting. In this case the HostKey setting specifies a public key, not a private key. Thus, attempting to load the private host key via sshkey_load_private() will fail, but loading the public key via sshkey_load_public() below will succeed, and the private key handling is relied on the agent. Suppress the confusing error message when attempting to load the private host key when an agent is used.
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This is an attempt to fix the problem reported in https://bugzilla.mindrot.org/show_bug.cgi?id=3964
Problem details (copied from bugzilla);
I am using a PKCS11 based hostkey for SSHD.
I am starting an ssh-agent on the host, then add the PKCS#11 provider and its key via 'ssh-add -s /path/to/pkcs11-provider' (one EC P-256 key gets added). Then I create the public SSH key from it using 'ssh-keygen -D /path/to/pkcs11-provider > /path/to/ssh_host_pkcs11_key.pub'.
Then I edit the SSHD config file as follows:
HostKey /path/to/ssh_host_pkcs11_key.pub
HostKeyAgent SSH_AUTH_SOCK
So the key specified with HostKey is a public key, and not a private key.
Environment variable SSH_AUTH_SOCK is set to the agent socket address.
When staring sshd, I get 'Unable to load host key "/path/to/ssh_host_pkcs11_key.pub": error in libcrypto'. However, processing continues and sshd is finally up fine.
Turning on debug (-d option) shows that it recognizes the agent key later on:
debug1: will rely on agent for hostkey /path/to/ssh_host_pkcs11_key.pub
debug1: agent host key #0: ecdsa-sha2-nistp256 SHA256:
So its not a functional problem, but the error message 'Unable to load host key "/path/to/ssh_host_pkcs11_key.pub": error in libcrypto' is confusing.
The doc at https://man.openbsd.org/sshd_config#HostKey states "It is also possible to specify public host key files instead. In this case operations on the private key will be delegated to an ssh-agent(1).". So it seems legit to specify a public key here when an agent based host key is used.
Fix:
Suppress the confusing error message when attempting to load the private host key when an agent is used.