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Highlights from the release notes are reproduced below. Some security and bug fixes were previously merged into FreeBSD and have been elided. See the upstream release notes for full details (https://www.openssh.com/releasenotes.html). --- Future deprecation notice ========================= OpenSSH plans to remove support for the DSA signature algorithm in early 2025. Potentially-incompatible changes -------------------------------- * sshd(8): the server will now block client addresses that repeatedly fail authentication, repeatedly connect without ever completing authentication or that crash the server. See the discussion of PerSourcePenalties below for more information. Operators of servers that accept connections from many users, or servers that accept connections from addresses behind NAT or proxies may need to consider these settings. * sshd(8): the server has been split into a listener binary, sshd(8), and a per-session binary "sshd-session". This allows for a much smaller listener binary, as it no longer needs to support the SSH protocol. As part of this work, support for disabling privilege separation (which previously required code changes to disable) and disabling re-execution of sshd(8) has been removed. Further separation of sshd-session into additional, minimal binaries is planned for the future. * sshd(8): several log messages have changed. In particular, some log messages will be tagged with as originating from a process named "sshd-session" rather than "sshd". * ssh-keyscan(1): this tool previously emitted comment lines containing the hostname and SSH protocol banner to standard error. This release now emits them to standard output, but adds a new "-q" flag to silence them altogether. * sshd(8): (portable OpenSSH only) sshd will no longer use argv[0] as the PAM service name. A new "PAMServiceName" sshd_config(5) directive allows selecting the service name at runtime. This defaults to "sshd". bz2101 New features ------------ * sshd(8): sshd(8) will now penalise client addresses that, for various reasons, do not successfully complete authentication. This feature is controlled by a new sshd_config(5) PerSourcePenalties option and is on by default. * ssh(8): allow the HostkeyAlgorithms directive to disable the implicit fallback from certificate host key to plain host keys. Portability ----------- * sshd(8): expose SSH_AUTH_INFO_0 always to PAM auth modules unconditionally. The previous behaviour was to expose it only when particular authentication methods were in use. * ssh(1), ssh-agent(8): allow the presence of the WAYLAND_DISPLAY environment variable to enable SSH_ASKPASS, similarly to the X11 DISPLAY environment variable. GHPR479 --- Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D48914
188 lines
4.7 KiB
Groff
188 lines
4.7 KiB
Groff
.\" $OpenBSD: ssh-keyscan.1,v 1.52 2024/06/17 08:30:29 djm Exp $
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.\"
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.\" Copyright 1995, 1996 by David Mazieres <dm@lcs.mit.edu>.
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.\"
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.\" Modification and redistribution in source and binary forms is
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.\" permitted provided that due credit is given to the author and the
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.\" OpenBSD project by leaving this copyright notice intact.
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.\"
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.Dd $Mdocdate: June 17 2024 $
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.Dt SSH-KEYSCAN 1
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.Os
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.Sh NAME
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.Nm ssh-keyscan
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.Nd gather SSH public keys from servers
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.Sh SYNOPSIS
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.Nm ssh-keyscan
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.Op Fl 46cDHqv
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.Op Fl f Ar file
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.Op Fl O Ar option
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.Op Fl p Ar port
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.Op Fl T Ar timeout
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.Op Fl t Ar type
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.Op Ar host | addrlist namelist
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.Sh DESCRIPTION
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.Nm
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is a utility for gathering the public SSH host keys of a number of
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hosts.
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It was designed to aid in building and verifying
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.Pa ssh_known_hosts
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files,
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the format of which is documented in
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.Xr sshd 8 .
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.Nm
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provides a minimal interface suitable for use by shell and perl
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scripts.
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.Pp
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.Nm
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uses non-blocking socket I/O to contact as many hosts as possible in
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parallel, so it is very efficient.
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The keys from a domain of 1,000
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hosts can be collected in tens of seconds, even when some of those
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hosts are down or do not run
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.Xr sshd 8 .
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For scanning, one does not need
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login access to the machines that are being scanned, nor does the
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scanning process involve any encryption.
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.Pp
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Hosts to be scanned may be specified by hostname, address or by CIDR
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network range (e.g. 192.168.16/28).
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If a network range is specified, then all addresses in that range will
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be scanned.
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.Pp
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The options are as follows:
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.Bl -tag -width Ds
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.It Fl 4
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Force
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.Nm
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to use IPv4 addresses only.
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.It Fl 6
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Force
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.Nm
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to use IPv6 addresses only.
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.It Fl c
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Request certificates from target hosts instead of plain keys.
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.It Fl D
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Print keys found as SSHFP DNS records.
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The default is to print keys in a format usable as a
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.Xr ssh 1
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.Pa known_hosts
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file.
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.It Fl f Ar file
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Read hosts or
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.Dq addrlist namelist
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pairs from
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.Ar file ,
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one per line.
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If
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.Sq -
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is supplied instead of a filename,
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.Nm
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will read from the standard input.
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Names read from a file must start with an address, hostname or CIDR network
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range to be scanned.
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Addresses and hostnames may optionally be followed by comma-separated name
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or address aliases that will be copied to the output.
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For example:
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.Bd -literal
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192.168.11.0/24
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10.20.1.1
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happy.example.org
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10.0.0.1,sad.example.org
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.Ed
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.It Fl H
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Hash all hostnames and addresses in the output.
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Hashed names may be used normally by
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.Xr ssh 1
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and
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.Xr sshd 8 ,
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but they do not reveal identifying information should the file's contents
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be disclosed.
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.It Fl O Ar option
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Specify a key/value option.
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At present, only a single option is supported:
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.Bl -tag -width Ds
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.It Cm hashalg Ns = Ns Ar algorithm
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Selects a hash algorithm to use when printing SSHFP records using the
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.Fl D
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flag.
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Valid algorithms are
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.Dq sha1
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and
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.Dq sha256 .
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The default is to print both.
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.El
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.It Fl p Ar port
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Connect to
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.Ar port
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on the remote host.
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.It Fl q
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Quiet mode:
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do not print server host name and banners in comments.
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.It Fl T Ar timeout
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Set the timeout for connection attempts.
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If
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.Ar timeout
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seconds have elapsed since a connection was initiated to a host or since the
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last time anything was read from that host, the connection is
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closed and the host in question considered unavailable.
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The default is 5 seconds.
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.It Fl t Ar type
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Specify the type of the key to fetch from the scanned hosts.
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The possible values are
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.Dq ecdsa ,
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.Dq ed25519 ,
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.Dq ecdsa-sk ,
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.Dq ed25519-sk ,
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or
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.Dq rsa .
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Multiple values may be specified by separating them with commas.
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The default is to fetch all the above key types.
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.It Fl v
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Verbose mode:
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print debugging messages about progress.
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.El
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.Pp
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If an ssh_known_hosts file is constructed using
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.Nm
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without verifying the keys, users will be vulnerable to
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.Em man in the middle
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attacks.
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On the other hand, if the security model allows such a risk,
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.Nm
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can help in the detection of tampered keyfiles or man in the middle
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attacks which have begun after the ssh_known_hosts file was created.
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.Sh FILES
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.Pa /etc/ssh/ssh_known_hosts
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.Sh EXAMPLES
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Print the RSA host key for machine
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.Ar hostname :
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.Pp
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.Dl $ ssh-keyscan -t rsa hostname
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.Pp
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Search a network range, printing all supported key types:
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.Pp
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.Dl $ ssh-keyscan 192.168.0.64/25
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.Pp
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Find all hosts from the file
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.Pa ssh_hosts
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which have new or different keys from those in the sorted file
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.Pa ssh_known_hosts :
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.Bd -literal -offset indent
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$ ssh-keyscan -t rsa,ecdsa,ed25519 -f ssh_hosts | \e
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sort -u - ssh_known_hosts | diff ssh_known_hosts -
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.Ed
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.Sh SEE ALSO
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.Xr ssh 1 ,
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.Xr sshd 8
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.Rs
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.%D 2006
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.%R RFC 4255
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.%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints
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.Re
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.Sh AUTHORS
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.An -nosplit
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.An David Mazieres Aq Mt dm@lcs.mit.edu
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wrote the initial version, and
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.An Wayne Davison Aq Mt wayned@users.sourceforge.net
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added support for protocol version 2.
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