2 # This should be sourced by bash (though we welcome changes to make it POSIX sh compliant)
4 # Monkeysphere ssh-proxycommand subcommand
6 # The monkeysphere scripts are written by:
7 # Jameson Rollins <jrollins@finestructure.net>
8 # Daniel Kahn Gillmor <dkg@fifthhorseman.net>
10 # They are Copyright 2008-2009, and are all released under the GPL,
13 # This is meant to be run as an ssh ProxyCommand to initiate a
14 # monkeysphere known_hosts update before an ssh connection to host is
15 # established. Can be added to ~/.ssh/config as follows:
16 # ProxyCommand monkeysphere ssh-proxycommand %h %p
18 # "marginal case" ouput in the case that there is not a full
19 # validation path to the host
20 output_no_valid_key() {
35 userID="ssh://${HOSTP}"
39 # retrieve the ssh key being offered by the host
40 sshKeyOffered=$(ssh-keyscan -t rsa -p "$PORT" "$HOST" 2>/dev/null \
41 | awk '{ print $2, $3 }')
43 # get the gpg info for userid
44 gpgOut=$(gpg_user --list-key --fixed-list-mode --with-colon \
45 --with-fingerprint --with-fingerprint \
46 ="$userID" 2>/dev/null)
50 -------------------- Monkeysphere warning -------------------
51 Monkeysphere found OpenPGP keys for this hostname, but none had full validity.
54 # if the host key is retrieved from the host, check against known
56 if [ "$sshKeyOffered" ] ; then
57 # find all 'pub' and 'sub' lines in the gpg output, which each
58 # represent a retrieved key for the user ID
59 echo "$gpgOut" | cut -d: -f1,2,5,10,12 | \
60 while IFS=: read -r type validity keyid uidfpr usage ; do
63 # get the ssh key of the gpg key
64 sshKeyGPG=$(gpg2ssh "$keyid")
66 # if one of keys found matches the one offered by the
67 # host, then output info
68 if [ "$sshKeyGPG" = "$sshKeyOffered" ] ; then
70 An OpenPGP key matching the ssh key offered by the host was found:
74 sshKeyGPGFile=$(msmktempfile)
75 printf "%s" "$sshKeyGPG" >"$sshKeyGPGFile"
76 sshFingerprint=$(ssh-keygen -l -f "$sshKeyGPGFile" | \
78 rm -f "$sshKeyGPGFile"
80 # get the sigs for the matching key
81 gpgSigOut=$(gpg_user --check-sigs \
82 --list-options show-uid-validity \
85 # output the sigs, but only those on the user ID
87 echo "$gpgSigOut" | awk '
89 if (match($0,"^pub")) { print; }
90 if (match($0,"^uid")) { ok=0; }
91 if (match($0,"^uid.*'$userID'$")) { ok=1; print; }
92 if (ok) { if (match($0,"^sig")) { print; } }
97 # output the other user IDs for reference
98 if (echo "$gpgSigOut" | grep "^uid" | grep -v -q "$userID") ; then
100 Other user IDs on this key:
103 echo "$gpgSigOut" | grep "^uid" | grep -v "$userID" | log info
107 # output ssh fingerprint
109 RSA key fingerprint is ${sshFingerprint}.
112 # this whole process is in a "while read"
113 # subshell. the only way to get information
114 # out of the subshell is to change the return
115 # code. therefore we return 1 here to
116 # indicate that a matching gpg key was found
117 # for the ssh key offered by the host
122 done || returnCode="$?"
124 # if no key match was made (and the "while read" subshell
125 # returned 1) output how many keys were found
126 if (( returnCode != 1 )) ; then
128 None of the found keys matched the key offered by the host.
129 Run the following command for more info about the found keys:
130 gpg --check-sigs --list-options show-uid-validity =${userID}
133 # FIXME: should we do anything extra here if the retrieved
134 # host key is actually in the known_hosts file and the ssh
135 # connection will succeed? Should the user be warned?
139 # if host key could not be retrieved from the host, output message
142 Could not retrieve RSA host key from $HOST.
148 -------------------- ssh continues below --------------------
153 # the ssh proxycommand function itself
156 if [ "$1" = '--no-connect' ] ; then
164 if [ -z "$HOST" ] ; then
165 log error "Host not specified."
169 if [ -z "$PORT" ] ; then
174 if [ "$PORT" != '22' ] ; then
175 HOSTP="${HOST}:${PORT}"
181 # specify keyserver checking. the behavior of this proxy command is
182 # intentionally different than that of running monkeyesphere normally,
183 # and keyserver checking is intentionally done under certain
184 # circumstances. This can be overridden by setting the
185 # MONKEYSPHERE_CHECK_KEYSERVER environment variable, or by setting the
186 # CHECK_KEYSERVER variable in the monkeysphere.conf file.
188 # if the host is in the gpg keyring...
189 if gpg_user --list-key ="${URI}" 2>&1 >/dev/null ; then
190 # do not check the keyserver
191 CHECK_KEYSERVER=${CHECK_KEYSERVER:="false"}
193 # if the host is NOT in the keyring...
195 # if the host key is found in the known_hosts file...
196 # FIXME: this only works for default known_hosts location
197 hostKey=$(ssh-keygen -F "$HOST" 2>/dev/null)
199 if [ "$hostKey" ] ; then
200 # do not check the keyserver
201 # FIXME: more nuanced checking should be done here to properly
202 # take into consideration hosts that join monkeysphere by
203 # converting an existing and known ssh key
204 CHECK_KEYSERVER=${CHECK_KEYSERVER:="false"}
206 # if the host key is not found in the known_hosts file...
208 # check the keyserver
209 CHECK_KEYSERVER=${CHECK_KEYSERVER:="true"}
213 # finally look in the MONKEYSPHERE_ environment variable for a
214 # CHECK_KEYSERVER setting to override all else
215 CHECK_KEYSERVER=${MONKEYSPHERE_CHECK_KEYSERVER:=$CHECK_KEYSERVER}
217 # update the known_hosts file for the host
219 update_known_hosts "$HOSTP" || returnCode="$?"
221 # output on depending on the return of the update-known_hosts
222 # subcommand, which is (ultimately) the return code of the
223 # update_known_hosts function in common
224 case "$returnCode" in
226 # acceptable host key found so continue to ssh
230 # no hosts at all found so also continue (drop through to
231 # regular ssh host verification)
235 # at least one *bad* host key (and no good host keys) was
236 # found, so output some usefull information
240 # anything else drop through
245 # FIXME: what about the case where monkeysphere successfully finds a
246 # valid key for the host and adds it to the known_hosts file, but a
247 # different non-monkeysphere key for the host already exists in the
248 # known_hosts, and it is this non-ms key that is offered by the host?
249 # monkeysphere will succeed, and the ssh connection will succeed, and
250 # the user will be left with the impression that they are dealing with
251 # a OpenPGP/PKI host key when in fact they are not. should we use
252 # ssh-keyscan to compare the keys first?
254 # exec a netcat passthrough to host for the ssh connection
255 if [ -z "$NO_CONNECT" ] ; then
256 if (which nc 2>/dev/null >/dev/null); then
257 exec nc "$HOST" "$PORT"
258 elif (which socat 2>/dev/null >/dev/null); then
259 exec socat STDIO "TCP:$HOST:$PORT"
261 echo "Neither netcat nor socat found -- could not complete monkeysphere-ssh-proxycommand connection to $HOST:$PORT" >&2