92 lines · bash
1#!/bin/bash2# SPDX-License-Identifier: GPL-2.03#4# Copyright © 2020, Microsoft Corporation. All rights reserved.5#6# Author: Mickaël Salaün <mic@linux.microsoft.com>7#8# Compute and print the To Be Signed (TBS) hash of a certificate. This is used9# as description of keys in the blacklist keyring to identify certificates.10# This output should be redirected, without newline, in a file (hash0.txt) and11# signed to create a PKCS#7 file (hash0.p7s). Both of these files can then be12# loaded in the kernel with.13#14# Exemple on a workstation:15# ./print-cert-tbs-hash.sh certificate-to-invalidate.pem > hash0.txt16# openssl smime -sign -in hash0.txt -inkey builtin-private-key.pem \17# -signer builtin-certificate.pem -certfile certificate-chain.pem \18# -noattr -binary -outform DER -out hash0.p7s19#20# Exemple on a managed system:21# keyctl padd blacklist "$(< hash0.txt)" %:.blacklist < hash0.p7s22 23set -u -e -o pipefail24 25CERT="${1:-}"26BASENAME="$(basename -- "${BASH_SOURCE[0]}")"27 28if [ $# -ne 1 ] || [ ! -f "${CERT}" ]; then29 echo "usage: ${BASENAME} <certificate>" >&230 exit 131fi32 33# Checks that it is indeed a certificate (PEM or DER encoded) and exclude the34# optional PEM text header.35if ! PEM="$(openssl x509 -inform DER -in "${CERT}" 2>/dev/null || openssl x509 -in "${CERT}")"; then36 echo "ERROR: Failed to parse certificate" >&237 exit 138fi39 40# TBSCertificate starts at the second entry.41# Cf. https://tools.ietf.org/html/rfc3280#section-4.142#43# Exemple of first lines printed by openssl asn1parse:44# 0:d=0 hl=4 l= 763 cons: SEQUENCE45# 4:d=1 hl=4 l= 483 cons: SEQUENCE46# 8:d=2 hl=2 l= 3 cons: cont [ 0 ]47# 10:d=3 hl=2 l= 1 prim: INTEGER :0248# 13:d=2 hl=2 l= 20 prim: INTEGER :3CEB2CB8818D968AC00EEFE195F0DF9665328B7B49# 35:d=2 hl=2 l= 13 cons: SEQUENCE50# 37:d=3 hl=2 l= 9 prim: OBJECT :sha256WithRSAEncryption51RANGE_AND_DIGEST_RE='522s/^\s*\([0-9]\+\):d=\s*[0-9]\+\s\+hl=\s*[0-9]\+\s\+l=\s*\([0-9]\+\)\s\+cons:\s*SEQUENCE\s*$/\1 \2/p;537s/^\s*[0-9]\+:d=\s*[0-9]\+\s\+hl=\s*[0-9]\+\s\+l=\s*[0-9]\+\s\+prim:\s*OBJECT\s*:\(.*\)$/\1/p;54'55 56RANGE_AND_DIGEST=($(echo "${PEM}" | \57 openssl asn1parse -in - | \58 sed -n -e "${RANGE_AND_DIGEST_RE}"))59 60if [ "${#RANGE_AND_DIGEST[@]}" != 3 ]; then61 echo "ERROR: Failed to parse TBSCertificate." >&262 exit 163fi64 65OFFSET="${RANGE_AND_DIGEST[0]}"66END="$(( OFFSET + RANGE_AND_DIGEST[1] ))"67DIGEST="${RANGE_AND_DIGEST[2]}"68 69# The signature hash algorithm is used by Linux to blacklist certificates.70# Cf. crypto/asymmetric_keys/x509_cert_parser.c:x509_note_pkey_algo()71DIGEST_MATCH=""72while read -r DIGEST_ITEM; do73 if [ -z "${DIGEST_ITEM}" ]; then74 break75 fi76 if echo "${DIGEST}" | grep -qiF "${DIGEST_ITEM}"; then77 DIGEST_MATCH="${DIGEST_ITEM}"78 break79 fi80done < <(openssl list -digest-commands | tr ' ' '\n' | sort -ur)81 82if [ -z "${DIGEST_MATCH}" ]; then83 echo "ERROR: Unknown digest algorithm: ${DIGEST}" >&284 exit 185fi86 87echo "${PEM}" | \88 openssl x509 -in - -outform DER | \89 dd "bs=1" "skip=${OFFSET}" "count=${END}" "status=none" | \90 openssl dgst "-${DIGEST_MATCH}" - | \91 awk '{printf "tbs:" $2}'92