#!/bin/bash -e
# vim: set tabstop=8 shiftwidth=4 softtabstop=4 expandtab smarttab colorcolumn=80:
#
# Copyright (c) 2017 Red Hat, Inc.
# Author: Nathaniel McCallum <npmccallum@redhat.com>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#

SUMMARY="Encrypts using a Tang binding server policy"

if [ "$1" == "--summary" ]; then
    echo "$SUMMARY"
    exit 0
fi

if [ -t 0 ]; then
    echo >&2
    echo "Usage: clevis encrypt tang CONFIG < PLAINTEXT > JWE" >&2
    echo >&2
    echo $SUMMARY >&2
    echo >&2
    echo "This command uses the following configuration properties:" >&2
    echo >&2
    echo "  url: <string>   The base URL of the Tang server (REQUIRED)" >&2
    echo >&2
    echo "  thp: <string>   The thumbprint of a trusted signing key" >&2
    echo >&2
    echo "  adv: <string>   A filename containing a trusted advertisement" >&2
    echo "  adv: <object>   A trusted advertisement (raw JSON)" >&2
    echo >&2
    echo "Obtaining the thumbprint of a trusted signing key is easy. If you" >&2
    echo "have access to the Tang server's database directory, simply do:" >&2
    echo >&2
    echo "    $ jose jwk thp -i \$DBDIR/\$SIG.jwk " >&2
    echo >&2
    echo "Alternatively, if you have certainty that your network connection" >&2
    echo "is not compromised (not likely), you can download the advertisement" >&2
    echo "yourself using:" >&2
    echo >&2
    echo "    $ curl -f \$URL/adv > adv.jws" >&2
    echo >&2
    exit 1
fi

if ! cfg=`jose fmt -j- -Oo- <<< "$1" 2>/dev/null`; then
    echo "Configuration is malformed!" >&2
    exit 1
fi

if ! url=`jose fmt -j- -Og url -u- <<< "$cfg"`; then
    echo "Missing the required 'url' property!" >&2
    exit 1
fi

thp=`jose fmt -j- -Og thp -Su- <<< "$cfg"` || true

### Get the advertisement
if jws=`jose fmt -j- -g adv -Oo- <<< "$cfg"`; then
    thp=${thp:-any}
elif jws=`jose fmt -j- -g adv -Su- <<< "$cfg"`; then
    if ! [ -f "$jws" ]; then
        echo "Advertisement file '$jws' not found!" >&2
        exit 1
    fi

    if ! jws=`jose fmt -j- -Oo- < "$jws"`; then
        echo "Advertisement file '$jws' is malformed!" >&2
        exit 1
    fi

    thp=${thp:-any}
elif ! jws=`curl -sfg "$url/adv/$thp"`; then
    echo "Unable to fetch advertisement: '$url/adv/$thp'!" >&2
    exit 1
fi

if ! jwks=`jose fmt -j- -Og payload -SyOg keys -AUo- <<< "$jws"`; then
    echo "Advertisement is malformed!" >&2
    exit 1
fi

### Check advertisement validity
ver=`jose jwk use -i- -r -u verify -o- <<< "$jwks"`
if ! jose jws ver -i "$jws" -k- -a <<< "$ver"; then
    echo "Advertisement is missing signatures!" >&2
    exit 1
fi

### Check advertisement trust
if [ -z "$thp" ]; then
    echo "The advertisement contains the following signing keys:" >&2
    echo >&2
    jose jwk thp -i- <<< "$ver" >&2
    echo >&2
    read -r -p "Do you wish to trust these keys? [ynYN] " ans < /dev/tty
    [[ "$ans" =~ ^[yY]$ ]] || exit 1

elif [ "$thp" != "any" ] && \
    ! jose jwk thp -i- -f "$thp" -o /dev/null <<< "$ver"; then
    echo "Trusted JWK '$thp' did not sign the advertisement!" >&2
    exit 1
fi

### Perform encryption
enc=`jose jwk use -i- -r -u deriveKey -o- <<< "$jwks"`
jose fmt -j "$enc" -Og keys -A || enc="{\"keys\":[$enc]}"

for jwk in `jose fmt -j- -Og keys -Af- <<< "$enc"`; do
    jwk=`jose fmt -j- -Od key_ops -o- <<< "$jwk"`
    jwk=`jose fmt -j- -Od alg -o- <<< "$jwk"`
    kid=`jose jwk thp -i- <<< "$jwk"`
    jwe='{"protected":{"alg":"ECDH-ES","enc":"A256GCM","clevis":{"pin":"tang","tang":{}}}}'
    jwe=`jose fmt -j "$jwe" -g protected -q "$kid" -s kid -UUo-`
    jwe=`jose fmt -j "$jwe" -g protected -g clevis -g tang -q "$url" -s url -UUUUo-`
    jwe=`jose fmt -j "$jwe" -g protected -g clevis -g tang -j- -s adv -UUUUo- <<< "$jwks"`
    exec jose jwe enc -i- -k- -I- -c < <(echo -n "$jwe$jwk"; cat)
done

echo "No exchange keys found!" >&2
exit 1