Each line in these files contains the following fields: markers
(optional), hostnames, bits, exponent, modulus, comment. The fields are
separated by spaces.
The marker is optional, but if it is present then it must be one of
``@cert-authority'', to indicate that the line contains a certification
authority (CA) key, or ``@revoked'', to indicate that the key contained
on the line is revoked and must not ever be accepted. Only one marker
should be used on a key line.
Hostnames is a comma-separated list of patterns (`*' and `?' act as
wildcards); each pattern in turn is matched against the canonical host
name (when authenticating a client) or against the user-supplied name
(when authenticating a server). A pattern may also be preceded by `!' to
indicate negation: if the host name matches a negated pattern, it is not
accepted (by that line) even if it matched another pattern on the line.
A hostname or address may optionally be enclosed within `[' and `]'
brackets then followed by `:' and a non-standard port number.
Alternately, hostnames may be stored in a hashed form which hides host
names and addresses should the file's contents be disclosed. Hashed
hostnames start with a `|' character. Only one hashed hostname may
appear on a single line and none of the above negation or wildcard
operators may be applied.
Bits, exponent, and modulus are taken directly from the RSA host key;
they can be obtained, for example, from /etc/ssh/ssh_host_key.pub. The
optional comment field continues to the end of the line, and is not used.
Lines starting with `#' and empty lines are ignored as comments.