Change PKI so that attestation certs are fully compliant.

Initially we generated the smallest certificate possible. Unfortunately sometimes attestation certificates are thoroughly checked and the FIDO x509v3 extensions must be present. This PR now creates a PKI (root CA and signing CA) with corresponding CRLs and also allows to create multiple batch certificates for the keys instead of a single one. The latest generated batch cert/key is automatically symlinked so that the previous documentation still holds.
google · Dec 14, 2023 · 33e24e1 · 33e24e1
1 parent af76345
commit 33e24e1
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Showing 6 changed files with 380 additions and 49 deletions.
diff --git a/setup.sh b/setup.sh
@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-# Copyright 2019 Google LLC
+# Copyright 2019-2023 Google LLC
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -40,7 +40,11 @@ check_command "$PIP"
 
 # Ensure we have certificates, keys, etc. so that the tests can run
 source tools/gen_key_materials.sh
-generate_crypto_materials N
+generate_pki N
+if [ ! -f "crypto_data/opensk.key" -o ! -f "crypto_data/opensk_cert.pem" ]
+then
+  generate_new_batch
+fi
 
 rustup show
 "$PIP" install --upgrade -r requirements.txt

diff --git a/tools/gen_key_materials.sh b/tools/gen_key_materials.sh
@@ -1,5 +1,5 @@
 #!/bin/bash
-# Copyright 2019 Google LLC
+# Copyright 2019-2023 Google LLC
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -13,20 +13,19 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-generate_crypto_materials () {
-  # OpenSSL ext file location
-  local openssl_ext_file=tools/openssl.ext
+generate_pki () {
+  # Curve parameters
+  local ecparams_file=crypto_data/ecparams.pem
   # OpenSK AAGUID
   local aaguid_file=crypto_data/aaguid.txt
 
   # Root CA key pair and certificate
-  local ca_priv_key=crypto_data/opensk_ca.key
-  local ca_cert_name=crypto_data/opensk_ca
+  local ca_priv_key=crypto_data/ca/root-ca/private/root-ca.key
+  local ca_cert_name=crypto_data/ca/root-ca
 
-  # Attestation key pair and certificate that will be embedded into the
-  # firmware. The certificate will be signed by the Root CA.
-  local opensk_key=crypto_data/opensk.key
-  local opensk_cert_name=crypto_data/opensk_cert
+  # Signing CA key pair and certificate
+  local signing_ca_priv_key=crypto_data/ca/signing-ca/private/signing-ca.key
+  local signing_ca_cert_name=crypto_data/ca/signing-ca
 
   # The upgrade private key is used for signing, the corresponding public key
   # will be COSE encoded and embedded into the firmware.
@@ -47,55 +46,107 @@ generate_crypto_materials () {
   set -e
 
   force_generate="$1"
-  mkdir -p crypto_data
-  if [ ! -f "${ca_priv_key}" ]
+  ask_for_password="$2"
+
+  if [ "${force_generate}" = "Y" ]
+  then
+    # Remove old OpenSK certs and CRL
+    rm -rf crypto_data/crl crypto_data/certs
+  fi
+
+  openssl_keypwd="-noenc"
+  openssl_batch="-batch"
+  if [ "${ask_for_password}" = "Y" ]
+  then
+    openssl_keypwd=""
+    openssl_batch=""
+  fi
+
+  # Create PKI directories
+  mkdir -p crypto_data/ca/root-ca/private crypto_data/ca/root-ca/db
+  mkdir -p crypto_data/ca/signing-ca/private crypto_data/ca/signing-ca/db
+  mkdir -p crypto_data/crl crypto_data/certs
+  chmod 700 crypto_data/ca/root-ca/private crypto_data/ca/signing-ca/private
+
+  # Prepare PKI databases
+  for fname in \
+    crypto_data/ca/root-ca/db/root-ca.db \
+    crypto_data/ca/root-ca/db/root-ca.db.attr \
+    crypto_data/ca/signing-ca/db/signing-ca.db \
+    crypto_data/ca/signing-ca/db/signing-ca.db.attr
+  do
+    if [ "${force_generate}" = "Y" -o ! -f "${fname}" ]
+    then
+      cp /dev/null "${fname}"
+    fi
+  done
+
+  # Initialize PKI serial numbers
+  for fname in \
+    crypto_data/ca/root-ca/db/root-ca.pem.srl \
+    crypto_data/ca/root-ca/db/root-ca.pem.srl \
+    crypto_data/ca/signing-ca/db/signing-ca.pem.srl \
+    crypto_data/ca/signing-ca/db/signing-ca.pem.srl
+  do
+    if [ "${force_generate}" = "Y" -o ! -f "${fname}" ]
+    then
+      echo 01 > "${fname}"
+    fi
+  done
+
+  # Generate AAGUID
+  if [ "${force_generate}" = "Y" -o ! -f "${aaguid_file}" ]
   then
-    "${openssl}" ecparam -genkey -name prime256v1 -out "${ca_priv_key}"
+    uuidgen > "${aaguid_file}"
   fi
 
-  if [ ! -f "${ca_cert_name}.pem" ]
+  if [ ! -f "${ecparams_file}" ]
   then
+    "${openssl}" ecparam -param_enc "named_curve" -name "prime256v1" -out "${ecparams_file}"
+  fi
+
+  if [ "${force_generate}" = "Y" -o ! -f "${ca_cert_name}.pem" ]
+  then
+    # Create root CA request and key pair
     "${openssl}" req \
       -new \
-      -key "${ca_priv_key}" \
+      -config tools/openssl/root-ca.conf \
       -out "${ca_cert_name}.csr" \
-      -subj "/CN=OpenSK CA"
-    "${openssl}" x509 \
-      -trustout \
-      -req \
-      -days 7305 \
+      -keyout "${ca_priv_key}" \
+      "${openssl_keypwd}" \
+      -newkey "ec:${ecparams_file}"
+
+    # Make root CA certificate
+    "${openssl}" ca \
+      -selfsign \
+      -config tools/openssl/root-ca.conf \
+      "${openssl_batch}" \
       -in "${ca_cert_name}.csr" \
-      -signkey "${ca_priv_key}" \
-      -outform pem \
       -out "${ca_cert_name}.pem" \
-      -sha256
+      -extensions root_ca_ext
   fi
 
-  if [ "${force_generate}" = "Y" -o ! -f "${opensk_key}" ]
-  then
-    "${openssl}" ecparam -genkey -name prime256v1 -out "${opensk_key}"
-  fi
-
-  if [ "${force_generate}" = "Y" -o ! -f "${opensk_cert_name}.pem" ]
+  if [ "${force_generate}" = "Y" -o ! -f "${signing_ca_cert_name}.pem" ]
   then
+    # Create signing CA request
     "${openssl}" req \
       -new \
-      -key "${opensk_key}" \
-      -out "${opensk_cert_name}.csr" \
-      -subj "/C=US/O=OpenSK/OU=Authenticator Attestation/CN=OpenSK Hacker Edition"
-    "${openssl}" x509 \
-      -req \
-      -days 3652 \
-      -in "${opensk_cert_name}.csr" \
-      -CA "${ca_cert_name}.pem" \
-      -extfile "${openssl_ext_file}" \
-      -CAkey "${ca_priv_key}" \
-      -CAcreateserial \
-      -outform pem \
-      -out "${opensk_cert_name}.pem" \
-      -sha256
+      -config tools/openssl/signing-ca.conf \
+      -out "${signing_ca_cert_name}.csr" \
+      -keyout "${signing_ca_priv_key}" \
+      "${openssl_keypwd}" \
+      -newkey "ec:${ecparams_file}"
+
+    # Make signing CA certificate
+    "${openssl}" ca \
+      -config tools/openssl/root-ca.conf \
+      "${openssl_batch}" \
+      -in "${signing_ca_cert_name}.csr" \
+      -out "${signing_ca_cert_name}.pem" \
+      -extensions signing_ca_ext
   fi
 
+  # Create firmware update key pair
   if [ "${force_generate}" = "Y" -o ! -f "${opensk_upgrade}" ]
   then
     "${openssl}" ecparam -genkey -name prime256v1 -out "${opensk_upgrade}"
@@ -106,11 +157,87 @@ generate_crypto_materials () {
   then
     "${openssl}" ec -in "${opensk_upgrade}" -pubout -out "${opensk_upgrade_pub}"
   fi
+}
 
-  if [ "${force_generate}" = "Y" -o ! -f "${aaguid_file}" ]
+generate_new_batch () {
+  local openssl=${OPENSSL:-$(which openssl)}
+  # Curve parameters
+  local ecparams_file=crypto_data/ecparams.pem
+  # OpenSK AAGUID
+  local aaguid_file=crypto_data/aaguid.txt
+
+  set -e
+
+  # We need openssl command to continue
+  if [ ! -x "${openssl}" ]
   then
-    uuidgen > "${aaguid_file}"
+    echo "Missing openssl command. Try to specify its full path using OPENSSL environment variable."
+    exit 1
   fi
+
+  if [ ! -f "${ecparams_file}" ]
+  then
+    echo "Missing curve parameters. Has the PKI been generated?"
+    exit 1
+  fi
+
+  if [ ! -f "${aaguid_file}" ]
+  then
+    echo "Missing AAGUID file."
+    exit 1
+  fi
+
+  batch_id=$(uuidgen | tr -d '-')
+  aaguid=$(tr -d '-' < "${aaguid_file}")
+
+  # Attestation key pair and certificate that will be embedded into the
+  # firmware. The certificate will be signed by the Root CA.
+  local opensk_key=certs/${batch_id}.key
+  local opensk_cert_name=certs/${batch_id}
+
+  # x509v3 extension values are passed through environment variables.
+  export OPENSK_AAGUID="${aaguid}"
+  # Comma separated values of supported transport for the batch attestation certificate.
+  # 0=BTC, 1=BLE, 2=USB, 3=NFC
+  # Default to USB only
+  export OPENSK_TRANSPORT="${OPENSK_TRANSPORT:-2}"  # comma separated values. 1=BLE, 2=USB, 3=NFC
+
+  ask_for_password="$1"  
+  openssl_keypwd="-noenc"
+  openssl_batch="-batch"
+  if [ "${ask_for_password}" = "Y" ]
+  then
+    openssl_keypwd=""
+    openssl_batch=""
+  fi
+
+  # Generate certificate request for the current batch
+  "${openssl}" req \
+    -new \
+    -config "tools/openssl/opensk.conf" \
+    -keyout "crypto_data/${opensk_key}" \
+    -out "crypto_data/${opensk_cert_name}.csr" \
+    "${openssl_keypwd}" \
+    -newkey "ec:${ecparams_file}"
+  # Sign it using signing-CA and injecting the AAGUID as an extension
+  "${openssl}" ca \
+    -config "tools/openssl/signing-ca.conf" \
+    "${openssl_batch}" \
+    -in "crypto_data/${opensk_cert_name}.csr" \
+    -out "crypto_data/${opensk_cert_name}.pem" \
+    -extensions "fido_key_ext"
+
+  # Force symlink to the latest batch
+  ln --symbolic --force "${opensk_cert_name}.pem" crypto_data/opensk_cert.pem
+  ln --symbolic --force "${opensk_key}" crypto_data/opensk.key
 }
 
-generate_crypto_materials "$1"
+if [ "X${1}" != "X" ]
+then
+  ask_for_password=${2:-N}
+  generate_pki $1 $ask_for_password
+  if [ "$1" = "Y" -o ! -f "crypto_data/opensk.key" -o ! -f "crypto_data/opensk_cert.pem" ]
+  then
+    generate_new_batch $ask_for_password
+  fi
+fi
diff --git a/tools/openssl.ext b/tools/openssl.ext
diff --git a/tools/openssl/opensk.conf b/tools/openssl/opensk.conf
@@ -0,0 +1,26 @@
+oid_section = OIDS
+
+[ OIDS ]
+fido_attestation = 1.3.6.1.4.1.45724.2.1.1
+fido_aaguid = 1.3.6.1.4.1.45724.1.1.4
+
+[ req ]
+encrypt_key = no
+default_md = sha256
+utf8 = yes
+string_mask = utf8only
+prompt = no
+distinguished_name = fido_dn
+req_extensions = fido_reqext
+
+[ fido_dn ]
+countryName = "US"
+organizationName = "OpenSK"
+organizationalUnitName = "Authenticator Attestation"
+commonName = "OpenSK Hacker Edition"
+
+[ fido_reqext ]
+keyUsage                = critical,digitalSignature
+subjectKeyIdentifier    = hash
+fido_attestation        = ASN1:FORMAT:BITLIST,BITSTRING:${ENV::OPENSK_TRANSPORT}
+fido_aaguid             = ASN1:FORMAT:HEX,OCTETSTRING:${ENV::OPENSK_AAGUID}