randombit_ocsp_forger.sh

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#!/bin/sh

# Helper script to generate forged OCSP responses

# that are signed by a random self-signed CA that

# has no authority to judge the revocation status

# of the given certificate.

# (C) 2022 Jack Lloyd

# (C) 2022 René Meusel (Rohde & Schwarz Cybersecurity)

# Botan is released under the Simplified BSD License (see license.txt)

if [ $# -ne 3 ]; then

    echo "Usage: $0 <victim's cert> <victim's cert's issuer> <valid/revoked>"

    exit 1

fi

if [ $(date "+%y%m%d") != "161118" ]; then

    echo "You need a time machine to run this script..."

    echo "Use libfaketime to set the system clock back to the 18th of November 2016"

    echo "Like so (path is for Ubuntu, might vary):"

    echo "  LD_PRELOAD=/usr/lib/x86_64-linux-gnu/faketime/libfaketime.so.1 FAKETIME=\"2016-11-18 12:00:00\" $0 $@"

    exit 1

fi

set -ex

Vcert="$1"

Vissuer="$2"

Vstatus="$3"

RQ="req.der"

RP="forged_response.der"

RPnocerts="forged_response_nocerts.der"

RPcakey="ca.key"

RPcacert="ca.pem"

RPcsrconf="cert_csr.conf"

RPcsr="cert.csr"

RPcertconf="cert.conf"

RPkey="cert.key"

RPcert="cert.pem"

RPindex="index.txt"

# create a forged Certificate Authority

openssl req -x509 \

            -sha256 -days 356 \

            -nodes \

            -newkey rsa:2048 \

            -subj "/CN=Forged OCSP CA/C=DE/L=Berlin" \

            -keyout $RPcakey -out $RPcacert

# create a self-signed certificate

openssl genrsa -out $RPkey 2048

cat > $RPcsrconf <<EOF

[ req ]

default_bits = 2048

prompt = no

default_md = sha256

req_extensions = req_ext

distinguished_name = dn

[ dn ]

C = DE

ST = Berlin

L = Berlin

O = Hackerspace

OU = OCSP Breaking Lab

CN = Forged OCSP Signer

[ req_ext ]

subjectAltName = @alt_names

[ alt_names ]

DNS.1 = ocsp.hackerspace.org

EOF

openssl req -new -key $RPkey -out $RPcsr -config $RPcsrconf

cat > $RPcertconf <<EOF

authorityKeyIdentifier=keyid,issuer

basicConstraints=CA:FALSE

keyUsage = digitalSignature

extendedKeyUsage=OCSPSigning

subjectAltName = @alt_names

[ alt_names ]

DNS.1 = ocsp.hackerspace.org

EOF

openssl x509 -req \

    -in $RPcsr \

    -CA $RPcacert -CAkey $RPcakey \

    -CAcreateserial -out $RPcert \

    -days 365 \

    -sha256 -extfile $RPcertconf

# mark victim's cert as "valid" or "revoked"

enddate=$(openssl x509 -in $Vcert -enddate -noout | sed 's/notAfter=//')

formatted_enddate=$(date -d "$enddate" "+%y%m%d%H%M%S")

serial=$(openssl x509 -in $Vcert -serial -noout | sed 's/serial=//')

subject=$(openssl x509 -in $Vcert -subject -nameopt "oneline,RFC2253" -noout | sed 's/subject=//')

if [ "$Vstatus" = "valid" ]; then

    echo "V\t${formatted_enddate}Z\t\t${serial}\tunknown\t${subject}" > $RPindex

elif [ "$Vstatus" = "revoked" ]; then

    formatted_currentdate=$(date "+%y%m%d%H%M%S")

    echo "R\t${formatted_enddate}Z\t${formatted_currentdate}Z\t${serial}\tunknown\t${subject}" > $RPindex

else

    echo "Don't understand OCSP response status: $Vstatus"

    exit 1

fi

# generate an OCSP response using the just-created certificate

openssl ocsp -issuer $Vissuer -cert $Vcert -reqout $RQ -text -no_nonce

openssl ocsp -reqin $RQ -rsigner $RPcert -rkey $RPkey -CA $Vissuer -index $RPindex -ndays 5 -respout $RP -text

openssl ocsp -reqin $RQ -rsigner $RPcert -rkey $RPkey -CA $Vissuer -index $RPindex -ndays 5 -respout $RPnocerts -resp_no_certs -text