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

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

CLEVIS_DEFAULT_THP_ALG=S1        # SHA-1
CLEVIS_ALTERNATIVE_THP_ALGS=S256 # SHA-256

trust=
[ -n "${2}" ] && [ "${2}" == "-y" ] && trust=yes

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="$(jose fmt -j "$jws" -Oo-)"; 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 "${trust}" ]; then
    if [ -z "$thp" ]; then
        echo "The advertisement contains the following signing keys:" >&2
        echo >&2
	jose jwk thp -i- -a "${CLEVIS_DEFAULT_THP_ALG}" <<< "$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 -a "${CLEVIS_DEFAULT_THP_ALG}" \
          <<< "$ver"; then
        # Thumbprint of trusted JWK did not match the signature. Let's check
        # alternative thumbprints generated with clevis supported hash
        # algorithms to be sure.
        for alg in ${CLEVIS_ALTERNATIVE_THP_ALGS}; do
            srv="$(jose jwk thp -i- -f "${thp}" -a "${alg}" <<< "${ver}")" \
                   && break
        done
        if [ -z "${srv}" ]; then
            echo "Trusted JWK '$thp' did not sign the advertisement!" >&2
            exit 1
        fi
    fi
fi

### Perform encryption
if ! enc="$(jose jwk use -i- -r -u deriveKey -o- <<< "$jwks")"; then
    echo "Key derivation key not available!" >&2
    exit 1
fi

jose fmt -j "$enc" -Og keys -A || enc="{\"keys\":[$enc]}"

if ! jwk="$(jose fmt -j- -Og keys -Af- <<< "$enc")"; then
    echo "No exchange keys found!" >&2
    exit 1
fi

jwk="$(jose fmt -j- -Od key_ops -o- <<< "$jwk")"
jwk="$(jose fmt -j- -Od alg -o- <<< "$jwk")"
kid="$(jose jwk thp -i- -a "${CLEVIS_DEFAULT_THP_ALG}"  <<< "$jwk")"
jwe='{"protected":{"alg":"ECDH-ES","enc":"A256GCM","clevis":{"pin":"tang","tang":{}}}}'
jwe="$(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"; /bin/cat)