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Description
Add OCSP checks to OpenVPN. Here is a little ditty that we were using on pfSense:
#!/usr/bin/env bash
#set -x
# Perform OCSP queries with OpenSSL
# given a certificate serial number.
# Full documentation and examples:
# http://www.openssl.org/docs/apps/ocsp.html
# OCSP responder URL (mandatory)
ocsp_url="http://ocsp.dimc.dhs.gov"
home="/root/ocsp"
#home="."
# Path to issuer certificate (mandatory)
# YOU MUST SET THIS TO THE PATH TO THE CA CERTIFICATE
issuer_CAs=("${home}/DHS_CA4_2021.pem" "${home}/DHS_CA4_2025.pem")
# use a nonce in the query, set to "-no_nonce" to not use it
nonce="-no_nonce"
# Verify the response
# YOU MUST SET THIS TO THE PATH TO THE RESPONSE VERIFICATION CERT
verify="${home}/dhsca_fullpath.pem"
# Depth in the certificate chain where the cert to verify is.
# Set to -1 to run the verification at every level (NOTE that
# in that case you need a more complex script as the various
# parameters for the query will likely be different at each level)
# "0" is the usual value here, where the client certificate is
check_depth=0
cur_depth=$1 # this is the *CURRENT* depth
common_name=$2 # CN in case you need it
# minimal sanity checks
err=0
for issuer in ${issuer_CAs[@]}; do
if [ -z "$issuer" ] || [ ! -e "$issuer" ]; then
echo "Error: issuer certificate undefined or not found!" >&2
err=1
fi
# build up part of the openssl ocsp command
issuers="${issuers} -issuer $issuer "
done
if [ -z "$verify" ] || [ ! -e "$verify" ]; then
echo "Error: verification certificate undefined or not found!" >&2
err=1
fi
if [ -z "$ocsp_url" ]; then
echo "Error: OCSP server URL not defined!" >&2
err=1
fi
if [ $err -eq 1 ]; then
echo "Did you forget to customize the variables in the script?" >&2
exit 1
fi
# begin
if [ $check_depth -eq -1 ] || [ $cur_depth -eq $check_depth ]; then
eval serial="\$tls_serial_${cur_depth}"
# To successfully complete, the following must happen:
#
# - The serial number must not be empty
# - The exit status of "openssl ocsp" must be zero
# - The output of the above command must contain the line
# "${serial}: good"
#
# Everything else fails with exit status 1.
if [ -n "$serial" ]; then
# This is only an example; you are encouraged to run this command (without
# redirections) manually against your or your CA's OCSP server to see how
# it responds, and adapt accordingly.
# Sample output that is assumed here:
#
# Response verify OK
# 4287405: good
# This Update: Apr 24 19:38:49 2010 GMT
# Next Update: May 2 14:23:42 2010 GMT
#
# NOTE: It is needed to check the exit code of OpenSSL explicitly. OpenSSL
# can in some circumstances give a "good" result if it could not
# reach the the OSCP server. In this case, the exit code will indicate
# if OpenSSL itself failed or not. If OpenSSL's exit code is not 0,
# don't trust the OpenSSL status.
status=$(openssl ocsp $issuers \
"$nonce" \
-CAfile "$verify" \
-url "$ocsp_url" \
-serial "${serial}" 2>&1)
if [ $? -eq 0 ]; then
# check if ocsp didn't report any errors
if echo "$status" | grep -Eq "(error|fail)"; then
exit 1
fi
# check that the reported status of certificate is ok
if echo "$status" | grep -Eq "^${serial}: good"; then
# check if signature on the OCSP response verified correctly
if echo "$status" | grep -Eq "^Response verify OK"; then
echo "Recieved good OCSP verification for certificate serial: ${serial}"
exit 0
fi
fi
fi
fi
# if we get here, something was wrong
exit 1
fiMetadata
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