#!/bin/sh

# rhesus: monkeysphere authorized_keys/known_hosts generating script
#
# Written by
# Jameson Rollins <jrollins@fifthhorseman.net>
#
# Copyright 2008, released under the GPL, version 3 or later

# all caps variables are meant to be user supplied (ie. from config
# file) and are considered global

PGRM=$(basename $0)

# date in UTF format if needed
DATE=$(date -u '+%FT%T')

# unset some environment variables that could screw things up
GREP_OPTIONS=

########################################################################
# FUNCTIONS
########################################################################

usage() {
cat <<EOF
usage: $PGRM k|known_hosts [host...]
       $PGRM a|authorized_keys [userid...]
Monkeysphere update of known_hosts or authorized_keys file.
If hosts/userids are specified, only those specified will be processed
EOF
}

failure() {
    echo "$1" >&2
    exit ${2:-'1'}
}

# write output to stdout
log() {
    echo -n "ms: "
    echo "$@"
}

# write output to stderr
loge() {
    echo -n "ms: " 1>&2
    echo "$@" 1>&2
}

# cut out all comments(#) and blank lines from standard input
meat() {
    grep -v -e "^[[:space:]]*#" -e '^$'
}

# cut a specified line from standard input
cutline() {
    head --line="$1" | tail -1
}

# retrieve all keys with given user id from keyserver
# FIXME: need to figure out how to retrieve all matching keys
# (not just first 5)
gpg_fetch_keys() {
    local id
    id="$1"
    echo 1,2,3,4,5 | \
	gpg --quiet --batch --command-fd 0 --with-colons \
	--keyserver "$KEYSERVER" \
	--search ="$id" >/dev/null 2>&1
}

# check that characters are in a string (in an AND fashion).
# used for checking key capability
# check_capability capability a [b...]
check_capability() {
    local capability
    local capcheck

    capability="$1"
    shift 1

    for capcheck ; do
	if echo "$capability" | grep -q -v "$capcheck" ; then
	    return 1
	fi
    done
    return 0
}

# convert escaped characters from gpg output back into original
# character
# FIXME: undo all escape character translation in with-colons gpg output
unescape() {
    echo "$1" | sed 's/\\x3a/:/'
}

# stand in until we get dkg's gpg2ssh program
gpg2ssh_tmp() {
    local mode
    local keyID
    local userID
    local host

    mode="$1"
    keyID="$2"
    userID="$3"

    if [ "$mode" = 'authorized_keys' ] ; then
	gpgkey2ssh "$keyID" | sed -e "s/COMMENT/${userID}/"

    # NOTE: it seems that ssh-keygen -R removes all comment fields from
    # all lines in the known_hosts file.  why?
    # NOTE: just in case, the COMMENT can be matched with the
    # following regexp:
    # '^MonkeySphere[[:digit:]]{4}(-[[:digit:]]{2}){2}T[[:digit:]]{2}(:[[:digit:]]{2}){2}$'
    elif [ "$mode" = 'known_hosts' ] ; then
	host=$(echo "$userID" | sed -e "s|ssh://||")
	echo -n "$host "; gpgkey2ssh "$keyID" | sed -e "s/COMMENT/MonkeySphere${DATE}/"
    fi
}

# userid and key policy checking
# the following checks policy on the returned keys
# - checks that full key has appropriate valididy (u|f)
# - checks key has specified capability (REQUIRED_KEY_CAPABILITY)
# - checks that particular desired user id has appropriate validity
# see /usr/share/doc/gnupg/DETAILS.gz
# expects global variable: "mode"
process_user_id() {
    local userID
    local cacheDir
    local requiredPubCapability
    local gpgOut
    local line
    local type
    local validity
    local keyid
    local uidfpr
    local capability
    local keyOK
    local pubKeyID
    local uidOK
    local keyIDs
    local userIDHash
    local keyID

    userID="$1"
    cacheDir="$2"

    requiredPubCapability=$(echo "$REQUIRED_KEY_CAPABILITY" | tr "[:lower:]" "[:upper:]")

    # fetch keys from keyserver, return 1 if none found
    gpg_fetch_keys "$userID" || return 1

    # output gpg info for (exact) userid and store
    gpgOut=$(gpg --fixed-list-mode --list-key --with-colons \
	="$userID" 2> /dev/null)

    # return 1 if there only "tru" lines are output from gpg
    if [ -z "$(echo "$gpgOut" | grep -v '^tru:')" ] ; then
	return 1
    fi

    # loop over all lines in the gpg output and process.
    # need to do it this way (as opposed to "while read...") so that
    # variables set in loop will be visible outside of loop
    for line in $(seq 1 $(echo "$gpgOut" | wc -l)) ; do

	# read the contents of the line
	type=$(echo "$gpgOut" | cutline "$line" | cut -d: -f1)
	validity=$(echo "$gpgOut" | cutline "$line" | cut -d: -f2)
	keyid=$(echo "$gpgOut" | cutline "$line" | cut -d: -f5)
	uidfpr=$(echo "$gpgOut" | cutline "$line" | cut -d: -f10)
	capability=$(echo "$gpgOut" | cutline "$line" | cut -d: -f12)

	# process based on record type
	case $type in
	    'pub') # primary keys
		# new key, wipe the slate
		keyOK=
		pubKeyID=
		uidOK=
		keyIDs=

		pubKeyID="$keyid"

		# check primary key validity
		if [ "$validity" != 'u' -a "$validity" != 'f' ] ; then
		    loge "  unacceptable primary key validity ($validity)."
		    continue
		fi
		# check capability is not Disabled...
		if check_capability "$capability" 'D' ; then
		    loge "  key disabled."
		    continue
		fi
		# check overall key capability
		# must be Encryption and Authentication
		if ! check_capability "$capability" $requiredPubCapability ; then
		    loge "  unacceptable primary key capability ($capability)."
		    continue
		fi

		# mark if primary key is acceptable
		keyOK=true

		# add primary key ID to key list if it has required capability
		if check_capability "$capability" $REQUIRED_KEY_CAPABILITY ; then
		    keyIDs[${#keyIDs[*]}]="$keyid"
		fi
		;;
	    'uid') # user ids
		# check key ok and we have key fingerprint
		if [ -z "$keyOK" ] ; then
		    continue
		fi
		# check key validity
		if [ "$validity" != 'u' -a "$validity" != 'f' ] ; then
		    continue
		fi
		# check the uid matches
		if [ "$(unescape "$uidfpr")" != "$userID" ] ; then
		    continue
		fi

		# mark if uid acceptable
		uidOK=true
		;;
	    'sub') # sub keys
		# add sub key ID to key list if it has required capability
		if check_capability "$capability" $REQUIRED_KEY_CAPABILITY ; then
		    keyIDs[${#keyIDs[*]}]="$keyid"
		fi
		;;
	esac
    done

    # hash userid for cache file name
    userIDHash=$(echo "$userID" | sha1sum | awk '{ print $1 }')

    # touch/clear key cache file
    # (will be left empty if there are noacceptable keys)
    > "$cacheDir"/"$userIDHash"."$pubKeyID"

    # for each acceptable key, write an ssh key line to the
    # key cache file
    if [ "$keyOK" -a "$uidOK" -a "${keyIDs[*]}" ] ; then
	for keyID in ${keyIDs[@]} ; do
	    # export the key with gpg2ssh
            # FIXME: needs to apply extra options for authorized_keys
	    # lines if specified
	    gpg2ssh_tmp "$mode" "$keyID" "$userID" >> "$cacheDir"/"$userIDHash"."$pubKeyID"

	    # hash the cache file if specified
	    if [ "$mode" = 'known_hosts' -a "$HASH_KNOWN_HOSTS" ] ; then
		ssh-keygen -H -f "$cacheDir"/"$userIDHash"."$pubKeyID" > /dev/null 2>&1
		rm "$cacheDir"/"$userIDHash"."$pubKeyID".old
	    fi
	done
    fi

    # echo the path to the key cache file
    echo "$cacheDir"/"$userIDHash"."$pubKeyID"
}

# process a host for addition to a known_host file
process_host() {
    local host
    local cacheDir
    local hostKeyCachePath

    host="$1"
    cacheDir="$2"

    log "processing host: '$host'"

    hostKeyCachePath=$(process_user_id "ssh://${host}" "$cacheDir")
    if [ $? = 0 ] ; then
	ssh-keygen -R "$host" -f "$USER_KNOWN_HOSTS"
	cat "$hostKeyCachePath" >> "$USER_KNOWN_HOSTS"
    fi
}

# process known_hosts file
# go through line-by-line, extract each host, and process with the
# host processing function
process_known_hosts() {
    local cacheDir
    local userID

    cacheDir="$1"

    # take all the hosts from the known_hosts file (first field),
    # grep out all the hashed hosts (lines starting with '|')
    cut -d ' ' -f 1 "$USER_KNOWN_HOSTS" | \
    grep -v '^|.*$' | \
    while IFS=, read -r -a hosts ; do
	# process each host
	for host in ${hosts[*]} ; do
	    process_host "$host" "$cacheDir"
	done
    done
}

# process an authorized_*_ids file
# go through line-by-line, extract each userid, and process
process_authorized_ids() {
    local authorizedIDsFile
    local cacheDir
    local userID
    local userKeyCachePath

    authorizedIDsFile="$1"
    cacheDir="$2"

    # clean out keys file and remake keys directory
    rm -rf "$cacheDir"
    mkdir -p "$cacheDir"

    # loop through all user ids in file
    # FIXME: needs to handle extra options if necessary
    cat "$authorizedIDsFile" | meat | \
    while read -r userID ; do
	# process the userid
	log "processing userid: '$userID'"
	userKeyCachePath=$(process_user_id "$userID" "$cacheDir")
	if [ -s "$userKeyCachePath" ] ; then
	    loge "  acceptable key/uid found."
	fi
    done
}

########################################################################
# MAIN
########################################################################

if [ -z "$1" ] ; then
    usage
    exit 1
fi

# mode given in first variable
mode="$1"
shift 1

# check user
if ! id -u "$USER" > /dev/null 2>&1 ; then
    failure "invalid user '$USER'."
fi

# set user home directory
HOME=$(getent passwd "$USER" | cut -d: -f6)

# set ms home directory
MS_HOME=${MS_HOME:-"$HOME"/.config/monkeysphere}

# load configuration file
MS_CONF=${MS_CONF:-"$MS_HOME"/monkeysphere.conf}
[ -e "$MS_CONF" ] && . "$MS_CONF"

# set config variable defaults
STAGING_AREA=${STAGING_AREA:-"$MS_HOME"}
AUTHORIZED_USER_IDS=${AUTHORIZED_USER_IDS:-"$MS_HOME"/authorized_user_ids}
GNUPGHOME=${GNUPGHOME:-"$HOME"/.gnupg}
KEYSERVER=${KEYSERVER:-subkeys.pgp.net}
REQUIRED_KEY_CAPABILITY=${REQUIRED_KEY_CAPABILITY:-"e a"}
USER_CONTROLLED_AUTHORIZED_KEYS=${USER_CONTROLLED_AUTHORIZED_KEYS:-"$HOME"/.ssh/authorized_keys}
USER_KNOWN_HOSTS=${USER_KNOWN_HOSTS:-"$HOME"/.ssh/known_hosts}
HASH_KNOWN_HOSTS=${HASH_KNOWN_HOSTS:-}

# export USER and GNUPGHOME variables, since they are used by gpg
export USER
export GNUPGHOME

# stagging locations
hostKeysCacheDir="$STAGING_AREA"/host_keys
userKeysCacheDir="$STAGING_AREA"/user_keys
msKnownHosts="$STAGING_AREA"/known_hosts
msAuthorizedKeys="$STAGING_AREA"/authorized_keys

# make sure gpg home exists with proper permissions
mkdir -p -m 0700 "$GNUPGHOME"

## KNOWN_HOST MODE
if [ "$mode" = 'known_hosts' -o "$mode" = 'k' ] ; then
    mode='known_hosts'

    cacheDir="$hostKeysCacheDir"

    log "user '$USER': monkeysphere known_hosts processing"

    # touch the known_hosts file to make sure it exists
    touch "$USER_KNOWN_HOSTS"

    # if hosts are specified on the command line, process just
    # those hosts
    if [ "$1" ] ; then
        for host ; do
	    process_host "$host" "$cacheDir"
	done

    # otherwise, if no hosts are specified, process the user
    # known_hosts file
    else
	if [ ! -s "$USER_KNOWN_HOSTS" ] ; then
	    failure "known_hosts file '$USER_KNOWN_HOSTS' is empty."
	fi
	process_known_hosts "$cacheDir"
    fi

## AUTHORIZED_KEYS MODE
elif [ "$mode" = 'authorized_keys' -o "$mode" = 'a' ] ; then
    mode='authorized_keys'

    cacheDir="$userKeysCacheDir"

    # check auth ids file
    if [ ! -s "$AUTHORIZED_USER_IDS" ] ; then
	log "authorized_user_ids file is empty or does not exist."
	exit
    fi

    log "user '$USER': monkeysphere authorized_keys processing"

    # if userids are specified on the command line, process just
    # those userids
    if [ "$1" ] ; then
	for userID ; do
	    if ! grep -q "$userID" "$AUTHORIZED_USER_IDS" ; then
		log "userid '$userID' not in authorized_user_ids file."
		continue
	    fi
	    log "processing user id: '$userID'"
	    process_user_id "$userID" "$cacheDir" > /dev/null
	done

    # otherwise, if no userids are specified, process the entire
    # authorized_user_ids file
    else
	process_authorized_ids "$AUTHORIZED_USER_IDS" "$cacheDir"
    fi

    # write output key file
    log "writing monkeysphere authorized_keys file... "
    touch "$msAuthorizedKeys"
    if [ "$(ls "$cacheDir")" ] ; then
	log -n "adding gpg keys... "
	cat "$cacheDir"/* > "$msAuthorizedKeys"
	echo "done."
    else
	log "no gpg keys to add."
    fi
    if [ "$USER_CONTROLLED_AUTHORIZED_KEYS" ] ; then
	if [ -s "$USER_CONTROLLED_AUTHORIZED_KEYS" ] ; then
	    log -n "adding user authorized_keys file... "
	    cat "$USER_CONTROLLED_AUTHORIZED_KEYS" >> "$msAuthorizedKeys"
	    echo "done."
	fi
    fi
    log "monkeysphere authorized_keys file generated:"
    log "$msAuthorizedKeys"

else
    failure "unknown command '$mode'."
fi