# -*-shell-script-*- # This should be sourced by bash (though we welcome changes to make it POSIX sh compliant) # Monkeysphere ssh-proxycommand subcommand # # The monkeysphere scripts are written by: # Jameson Rollins <jrollins@finestructure.net> # Daniel Kahn Gillmor <dkg@fifthhorseman.net> # # They are Copyright 2008-2009, and are all released under the GPL, # version 3 or later. # This is meant to be run as an ssh ProxyCommand to initiate a # monkeysphere known_hosts update before an ssh connection to host is # established. Can be added to ~/.ssh/config as follows: # ProxyCommand monkeysphere ssh-proxycommand %h %p # output the key info, including the RSA fingerprint show_key_info() { local keyid="$1" local sshKeyGPGFile local sshFingerprint local gpgSigOut local otherUids # get the ssh key of the gpg key sshKeyGPGFile=$(msmktempfile) gpg2ssh "$keyid" >"$sshKeyGPGFile" sshFingerprint=$(ssh-keygen -l -f "$sshKeyGPGFile" | \ awk '{ print $2 }') rm -f "$sshKeyGPGFile" # get the sigs for the matching key gpgSigOut=$(gpg_user --check-sigs \ --list-options show-uid-validity \ "$keyid") echo | log info # output the sigs, but only those on the user ID # we are looking for echo "$gpgSigOut" | awk ' { if (match($0,"^pub")) { print; } if (match($0,"^uid")) { ok=0; } if (match($0,"^uid.*'$userID'$")) { ok=1; print; } if (ok) { if (match($0,"^sig")) { print; } } } ' # output ssh fingerprint cat <<EOF RSA key fingerprint is ${sshFingerprint}. EOF # output the other user IDs for reference otherUids=$(echo "$gpgSigOut" | grep "^uid" | grep -v "$userID") if [ "$otherUids" ] ; then log info <<EOF Other user IDs on this key: EOF echo "$otherUids" | log info fi } # "marginal case" ouput in the case that there is not a full # validation path to the host output_no_valid_key() { local userID local sshKeyOffered local gpgOut local type local validity local keyid local uidfpr local usage local sshKeyGPG local tmpkey local returnCode=0 userID="ssh://${HOSTP}" LOG_PREFIX= # retrieve the ssh key being offered by the host sshKeyOffered=$(ssh-keyscan -t rsa -p "$PORT" "$HOST" 2>/dev/null \ | awk '{ print $2, $3 }') # get the gpg info for userid gpgOut=$(gpg_user --list-key --fixed-list-mode --with-colon \ --with-fingerprint --with-fingerprint \ ="$userID" 2>/dev/null) # output header log info <<EOF -------------------- Monkeysphere warning ------------------- Monkeysphere found OpenPGP keys for this hostname, but none had full validity. EOF # output message if host key could not be retrieved from the host if [ -z "$sshKeyOffered" ] ; then log info <<EOF Could not retrieve RSA host key from $HOST. EOF # check that there are any marginally valid keys if echo "$gpgOut" | egrep -q '^(pub|sub):(m|f|u):' ; then log info <<EOF The following keys were found with marginal validity: EOF fi fi # find all keys in the gpg output ('pub' and 'sub' lines) and # output the ones that match the host key or that have marginal # validity echo "$gpgOut" | cut -d: -f1,2,5,10,12 | \ while IFS=: read -r type validity keyid uidfpr usage ; do case $type in 'pub'|'sub') # get the ssh key of the gpg key sshKeyGPG=$(gpg2ssh "$keyid") # if a key was retrieved from the host... if [ "$sshKeyOffered" ] ; then # if one of the keys matches the one offered by # the host, then output info and return if [ "$sshKeyGPG" = "$sshKeyOffered" ] ; then log info <<EOF An OpenPGP key matching the ssh key offered by the host was found: EOF show_key_info "$keyid" | log info # this whole process is in a "while read" # subshell. the only way to get information # out of the subshell is to change the return # code. therefore we return 1 here to # indicate that a matching gpg key was found # for the ssh key offered by the host return 1 fi # else if a key was not retrieved from the host... else # and the current key is marginal, show info if [ "$validity" = 'm' ] \ || [ "$validity" = 'f' ] \ || [ "$validity" = 'u' ] ; then show_key_info "$keyid" | log info fi fi ;; esac done || returnCode="$?" # if no key match was made (and the "while read" subshell # returned 1) output how many keys were found if (( returnCode == 1 )) ; then echo | log info else # if a key was retrieved, but didn't match, note this if [ "$sshKeyOffered" ] ; then log info <<EOF None of the found keys matched the key offered by the host. EOF fi # note how many invalid keys were found nInvalidKeys=$(echo "$gpgOut" | egrep '^(pub|sub):[^(m|f|u)]:' | wc -l) if ((nInvalidKeys > 0)) ; then log info <<EOF Keys found with less than marginal validity: $nInvalidKeys EOF fi log info <<EOF Run the following command for more info about the found keys: gpg --check-sigs --list-options show-uid-validity =${userID} EOF # FIXME: should we do anything extra here if the retrieved # host key is actually in the known_hosts file and the ssh # connection will succeed? Should the user be warned? # prompted? fi # output footer log info <<EOF -------------------- ssh continues below -------------------- EOF } # the ssh proxycommand function itself ssh_proxycommand() { if [ "$1" = '--no-connect' ] ; then NO_CONNECT='true' shift 1 fi HOST="$1" PORT="$2" if [ -z "$HOST" ] ; then log error "Host not specified." usage exit 255 fi if [ -z "$PORT" ] ; then PORT=22 fi # set the host URI if [ "$PORT" != '22' ] ; then HOSTP="${HOST}:${PORT}" else HOSTP="${HOST}" fi URI="ssh://${HOSTP}" # specify keyserver checking. the behavior of this proxy command is # intentionally different than that of running monkeyesphere normally, # and keyserver checking is intentionally done under certain # circumstances. This can be overridden by setting the # MONKEYSPHERE_CHECK_KEYSERVER environment variable, or by setting the # CHECK_KEYSERVER variable in the monkeysphere.conf file. # if the host is in the gpg keyring... if gpg_user --list-key ="${URI}" &>/dev/null ; then # do not check the keyserver CHECK_KEYSERVER=${CHECK_KEYSERVER:="false"} # if the host is NOT in the keyring... else # if the host key is found in the known_hosts file... hostKey=$( [ ! -r "$KNOWN_HOSTS" ] || ssh-keygen -F "$HOST" -f "$KNOWN_HOSTS" 2>/dev/null) if [ "$hostKey" ] ; then # do not check the keyserver # FIXME: more nuanced checking should be done here to properly # take into consideration hosts that join monkeysphere by # converting an existing and known ssh key CHECK_KEYSERVER=${CHECK_KEYSERVER:="false"} # if the host key is not found in the known_hosts file... else # check the keyserver CHECK_KEYSERVER=${CHECK_KEYSERVER:="true"} fi fi # finally look in the MONKEYSPHERE_ environment variable for a # CHECK_KEYSERVER setting to override all else CHECK_KEYSERVER=${MONKEYSPHERE_CHECK_KEYSERVER:=$CHECK_KEYSERVER} # update the known_hosts file for the host local returnCode=0 update_known_hosts "$HOSTP" || returnCode="$?" # output on depending on the return of the update-known_hosts # subcommand, which is (ultimately) the return code of the # update_known_hosts function in common case "$returnCode" in 0) # acceptable host key found so continue to ssh true ;; 1) # no hosts at all found so also continue (drop through to # regular ssh host verification) true ;; 2) # at least one *bad* host key (and no good host keys) was # found, so output some usefull information output_no_valid_key ;; *) # anything else drop through true ;; esac # FIXME: what about the case where monkeysphere successfully finds a # valid key for the host and adds it to the known_hosts file, but a # different non-monkeysphere key for the host already exists in the # known_hosts, and it is this non-ms key that is offered by the host? # monkeysphere will succeed, and the ssh connection will succeed, and # the user will be left with the impression that they are dealing with # a OpenPGP/PKI host key when in fact they are not. should we use # ssh-keyscan to compare the keys first? # exec a netcat passthrough to host for the ssh connection if [ -z "$NO_CONNECT" ] ; then if (type nc &>/dev/null); then exec nc "$HOST" "$PORT" elif (type socat &>/dev/null); then exec socat STDIO "TCP:$HOST:$PORT" else echo "Neither netcat nor socat found -- could not complete monkeysphere-ssh-proxycommand connection to $HOST:$PORT" >&2 exit 255 fi fi }