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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/>.
- #
- [ $# -eq 1 ] && [ "$1" == "--summary" ] && exit 2
- if [ -t 0 ]; then
- exec >&2
- echo
- echo "Usage: clevis decrypt tang < JWE > PLAINTEXT"
- echo
- exit 2
- fi
- read -r -d . hdr
- if ! jhd="$(jose b64 dec -i- <<< "$hdr")"; then
- echo "Error decoding JWE protected header!" >&2
- exit 1
- fi
- if [ "$(jose fmt -j- -Og clevis -g pin -u- <<< "$jhd")" != "tang" ]; then
- echo "JWE pin mismatch!" >&2
- exit 1
- fi
- if ! clt="$(jose fmt -j- -Og epk -Oo- <<< "$jhd")"; then
- echo "JWE missing required 'epk' header parameter!" >&2
- exit 1
- fi
- if ! kid="$(jose fmt -j- -Og kid -Su- <<< "$jhd")"; then
- echo "JWE missing required 'kid' header parameter!" >&2
- exit 1
- fi
- # Tang advertisement validation.
- if ! keys="$(jose fmt -j- -Og clevis -g tang -g adv -Oo- <<< "${jhd}")"; then
- echo "JWE missing required 'clevis.tang.adv' header parameter!" >&2
- exit 1
- fi
- # Check if the thumbprint we have in `kid' is in the advertised keys.
- CLEVIS_DEFAULT_THP_ALG=S256 # SHA-256.
- CLEVIS_DEFAULT_THP_LEN=43 # Length of SHA-256 thumbprint.
- CLEVIS_ALTERNATIVE_THP_ALGS=S1 # SHA-1.
- # Issue a warning if we are using a hash that has a shorter length than the
- # default one.
- if [ "${#kid}" -lt "${CLEVIS_DEFAULT_THP_LEN}" ]; then
- echo "WARNING: tang using a deprecated hash for the JWK thumbprints" >&2
- fi
- if ! srv="$(jose jwk thp -i- -f "${kid}" -a "${CLEVIS_DEFAULT_THP_ALG}" \
- <<< "${keys}")"; then
- # `kid' thumprint not in the advertised keys, but it's possible it was
- # generated using a different algorithm than the default one.
- # Let us try the alternative supported algorithms to make sure `kid'
- # really is not part of the advertised keys.
- for alg in ${CLEVIS_ALTERNATIVE_THP_ALGS}; do
- srv="$(jose jwk thp -i- -f "$kid" -a "${alg}" <<< "${keys}")" && break
- done
- if [ -z "${srv}" ]; then
- echo "JWE header validation of 'clevis.tang.adv' failed: key thumbprint does not match" >&2
- exit 1
- fi
- fi
- if ! url="$(jose fmt -j- -Og clevis -g tang -g url -Su- <<< "$jhd")"; then
- echo "JWE missing required 'clevis.tang.url' header parameter!" >&2
- exit 1
- fi
- if ! crv="$(jose fmt -j- -Og crv -Su- <<< "$clt")"; then
- echo "Unable to determine EPK's curve!" >&2
- exit 1
- fi
- if ! eph="$(jose jwk gen -i "{\"alg\":\"ECMR\",\"crv\":\"$crv\"}")"; then
- echo "Error generating ephemeral key!" >&2
- exit 1
- fi
- xfr="$(jose jwk exc -i '{"alg":"ECMR"}' -l- -r- <<< "$clt$eph")"
- url="$url/rec/$kid"
- ct="Content-Type: application/jwk+json"
- if ! rep="$(curl -sfg -X POST -H "$ct" --data-binary @- "$url" <<< "$xfr")"; then
- echo "Error communicating with the server!" >&2
- exit 1
- fi
- if ! rep="$(jose fmt -j- -Og kty -q EC -EUUg crv -q "$crv" -EUUo- <<< "$rep")"; then
- echo "Received invalid server reply!" >&2
- exit 1
- fi
- tmp="$(jose jwk exc -i '{"alg":"ECMR"}' -l- -r- <<< "$eph$srv")"
- rep="$(jose jwk pub -i- <<< "$rep")"
- jwk="$(jose jwk exc -l- -r- <<< "$rep$tmp")"
- (echo -n "$jwk$hdr."; /bin/cat) | jose jwe dec -k- -i-
- exit $?
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