#!/bin/bash
# Copyright 2026 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#

#
# Creates a private root CA and, issued by it, EC P-256 keys and certificates
# for a C2PA claim signer and a Time Stamping Authority (TSA). The output is
# intended for local testing of tools:asset_write and tools:c2pa_validate only.
#
# Usage: create_test_pki.sh [output_dir]
#
# output_dir defaults to ./test_pki and must not already contain keys.
#
# The certificates follow the C2PA certificate profile checked by the
# validator: X.509 v3 with the digitalSignature key usage. The claim signer
# certificate carries the C2PA claim signing EKU (1.3.6.1.4.1.62558.2.1) and no
# anyExtendedKeyUsage. The TSA certificate carries a critical timeStamping EKU
# as required by RFC 3161.
#
# Keep root_ca_key.pem private: anyone holding it can issue certificates that
# validators configured with root_ca_cert.pem will trust.
#
# Requires OpenSSL 1.1.1 or later.

set -euo pipefail

readonly CURVE="P-256"
readonly ROOT_CA_DAYS=3650
readonly LEAF_DAYS=365
readonly ORGANIZATION="Credentio Test"

#######################################
# Writes the OpenSSL config with the certificate extensions for each profile.
# Arguments:
#   Path of the config file to write.
#######################################
write_openssl_config() {
  cat > "$1" <<'EOF'
[ req ]
distinguished_name = req_dn

[ req_dn ]

[ root_ca ]
basicConstraints       = critical, CA:TRUE
keyUsage               = critical, keyCertSign, cRLSign
subjectKeyIdentifier   = hash

# C2PA claim signer: digitalSignature KU and the C2PA claim signing EKU.
[ claim_signer ]
basicConstraints       = critical, CA:FALSE
keyUsage               = critical, digitalSignature
extendedKeyUsage       = 1.3.6.1.4.1.62558.2.1
subjectKeyIdentifier   = hash
authorityKeyIdentifier = keyid:always

# RFC 3161 TSA: timeStamping must be the only EKU and marked critical.
[ tsa ]
basicConstraints       = critical, CA:FALSE
keyUsage               = critical, digitalSignature
extendedKeyUsage       = critical, timeStamping
subjectKeyIdentifier   = hash
authorityKeyIdentifier = keyid:always
EOF
}

#######################################
# Generates an EC private key in PKCS#8 PEM format.
# Arguments:
#   Output key path.
#######################################
generate_key() {
  openssl genpkey -algorithm EC -pkeyopt "ec_paramgen_curve:${CURVE}" \
    -out "$1" 2>/dev/null
  chmod 600 "$1"
}

#######################################
# Creates the self-signed root CA key and certificate.
# Arguments:
#   Output directory.
#######################################
create_root_ca() {
  local dir="$1"
  generate_key "${dir}/root_ca_key.pem"
  openssl req -x509 -new -key "${dir}/root_ca_key.pem" -sha256 \
    -days "${ROOT_CA_DAYS}" \
    -subj "/O=${ORGANIZATION}/CN=${ORGANIZATION} Root CA" \
    -config "${dir}/openssl.cnf" -extensions root_ca \
    -out "${dir}/root_ca_cert.pem"
}

#######################################
# Creates a key and a certificate issued by the root CA.
# Arguments:
#   Output directory.
#   Name of the profile section in openssl.cnf; also the output file prefix.
#   Common name of the certificate subject.
#######################################
issue_leaf() {
  local dir="$1"
  local profile="$2"
  local common_name="$3"

  generate_key "${dir}/${profile}_key.pem"
  openssl req -new -key "${dir}/${profile}_key.pem" \
    -subj "/O=${ORGANIZATION}/CN=${common_name}" \
    -config "${dir}/openssl.cnf" |
    openssl x509 -req -sha256 -days "${LEAF_DAYS}" \
      -CA "${dir}/root_ca_cert.pem" -CAkey "${dir}/root_ca_key.pem" \
      -set_serial "0x$(openssl rand -hex 16)" \
      -extfile "${dir}/openssl.cnf" -extensions "${profile}" \
      -out "${dir}/${profile}_cert.pem" 2>/dev/null
}

main() {
  if [[ $# -gt 1 ]]; then
    echo "Usage: $0 [output_dir]" >&2
    exit 1
  fi
  local dir="${1:-test_pki}"

  if ! command -v openssl >/dev/null; then
    echo "Error: openssl not found in PATH." >&2
    exit 1
  fi
  if compgen -G "${dir}/*_key.pem" >/dev/null; then
    echo "Error: ${dir} already contains keys; refusing to overwrite." >&2
    exit 1
  fi

  mkdir -p "${dir}"
  write_openssl_config "${dir}/openssl.cnf"
  create_root_ca "${dir}"
  issue_leaf "${dir}" claim_signer "${ORGANIZATION} Claim Signer"
  issue_leaf "${dir}" tsa "${ORGANIZATION} TSA"
  openssl verify -CAfile "${dir}/root_ca_cert.pem" \
    "${dir}/claim_signer_cert.pem" "${dir}/tsa_cert.pem" >/dev/null

  local abs_dir
  abs_dir="$(cd "${dir}" && pwd)"
  cat <<EOF
Created test PKI in ${abs_dir}:

  asset_write flags:
    --claim_signer_key=${abs_dir}/claim_signer_key.pem
    --claim_signer_cert=${abs_dir}/claim_signer_cert.pem
    --tsa_key=${abs_dir}/tsa_key.pem
    --tsa_cert=${abs_dir}/tsa_cert.pem

  c2pa_validate flags:
    --claim_signer_trust=${abs_dir}/root_ca_cert.pem
    --tsa_trust=${abs_dir}/root_ca_cert.pem

These credentials are for local testing only. Keep root_ca_key.pem private.
EOF
}

main "$@"