ssh-keysign is used by ssh(1) to access the local host keys and generate the digital signature required during host-based authentication with SSH protocol version 2. This signature is of data that includes, among other items, the name of the client host and the name of the client user.
ssh-keysign is disabled by default and can be enabled only in the global client configuration file /etc/ssh/ssh_config by setting HostbasedAuthentication to yes.
Controls whether ssh-keysign is enabled.
These files contain the private parts of the host keys used to generate the digital signature. They should be owned by root, readable only by root, and not accessible to others. Because they are readable only by root, ssh-keysign must be set-uid root if host-based authentication is used.
ssh-keysign will not sign host-based authentication data under the following conditions:
If the HostbasedAuthentication client configuration parameter is not set to yes in /etc/ssh/ssh_config. This setting cannot be overriden in users' ~/.ssh/ssh_config files.
If the client hostname and username in /etc/ssh/ssh_config do not match the canonical hostname of the client where ssh-keysign is invoked and the name of the user invoking ssh-keysign.
In spite of ssh-keysign's restrictions on the contents of the host-based authentication data, there remains the ability of users to use it as an avenue for obtaining the client's private host keys. For this reason host-based authentication is turned off by default.
See attributes(5) for descriptions of the following attributes:
Markus Friedl, email@example.com
ssh-keysign first appeared in Ox 3.2.