Internet DRAFT - draft-moskowitz-ec-pki
draft-moskowitz-ec-pki
wg TBD R. Moskowitz
Internet-Draft HTT Consulting
Intended status: Informational H. Birkholz
Expires: 4 August 2024 Fraunhofer SIT
M. Richardson
Sandelman
1 February 2024
Guide for building an EC PKI
draft-moskowitz-ec-pki-02
Abstract
This memo provides a guide for building a PKI (Public Key
Infrastructure) of EC certificates using openSSL. Certificates in
this guide can use either ECDSA or EdDSA. Along with common End
Entity certificates, this guide provides instructions for creating
IEEE 802.1AR iDevID Secure Device certificates.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 4 August 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Terminology . . . . . . . . . . . . . . . . 4
2.2. Notations . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Definitions . . . . . . . . . . . . . . . . . . . . . . . 4
3. Comparing ECDSA and EdDSA certificates . . . . . . . . . . . 4
4. The Basic PKI feature set . . . . . . . . . . . . . . . . . . 4
5. Getting started and the Root level . . . . . . . . . . . . . 5
5.1. Setting up the Environment . . . . . . . . . . . . . . . 6
5.2. Create the Root Certificate . . . . . . . . . . . . . . . 7
6. The Intermediate level . . . . . . . . . . . . . . . . . . . 9
6.1. Setting up the Intermediate Certificate Environment . . . 9
6.2. Create the Intermediate Certificate . . . . . . . . . . . 10
6.3. Create a Server EE Certificate . . . . . . . . . . . . . 11
6.4. Create a Client EE Certificate . . . . . . . . . . . . . 13
7. The 802.1AR Intermediate level . . . . . . . . . . . . . . . 14
7.1. Setting up the 802.1AR Intermediate Certificate
Environment . . . . . . . . . . . . . . . . . . . . . . . 14
7.2. Create an 802.1AR iDevID Certificate . . . . . . . . . . 14
8. Setting up a CRL for an Intermediate CA . . . . . . . . . . . 16
8.1. Create (or recreate) the CRL . . . . . . . . . . . . . . 16
8.2. Revoke a Certificate . . . . . . . . . . . . . . . . . . 17
9. Setting up OCSP for an Intermediate CA . . . . . . . . . . . 17
9.1. Create the OCSP Certificate . . . . . . . . . . . . . . . 17
9.2. Revoke a Certificate . . . . . . . . . . . . . . . . . . 19
9.3. Testing OCSP with Openssl . . . . . . . . . . . . . . . . 19
10. Footnotes . . . . . . . . . . . . . . . . . . . . . . . . . . 19
10.1. Certificate Serial Number . . . . . . . . . . . . . . . 20
10.2. Some OpenSSL config file limitations . . . . . . . . . . 21
10.3. subjectAltName support now works . . . . . . . . . . . . 21
10.4. Certificates with only subjectAltName . . . . . . . . . 21
10.5. DER support, or lack thereof . . . . . . . . . . . . . . 21
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
12. Security Considerations . . . . . . . . . . . . . . . . . . . 22
12.1. Adequate Randomness . . . . . . . . . . . . . . . . . . 22
12.2. Key pair Theft . . . . . . . . . . . . . . . . . . . . . 22
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
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14. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
14.1. Normative References . . . . . . . . . . . . . . . . . . 23
14.2. Informative References . . . . . . . . . . . . . . . . . 24
Appendix A. OpenSSL config file . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction
The IETF has a plethora of security solutions targeted at IoT. Yet
all too many IoT products are tested and deployed with no or
improperly configured security. In particular resource constrained
IoT devices and non-IP IoT networks have not been well served in the
IETF.
Additionally, more IETF (e.g. DOTS, NETCONF) efforts are requiring
secure identities, but are vague on the nature of these identities
other than to recommend use of X.509 digital certificates and perhaps
TLS.
This effort provides the steps, using the openSSL application, to
create such a PKI of ECDSA [NIST.FIPS.186-5], ED25519, or ED448
([RFC8032] and [NIST.FIPS.186-5]) certificates. The goal is that any
developer or tester can follow these steps, create the basic objects
needed and establish the validity of the standard/program design.
This guide can even be used to create a production PKI, though
additional steps need to be taken. This could be very useful to a
small vendor needing to include 802.1AR [IEEE 802.1AR] that
references [RFC4108] iDevIDs in their product (Note: EdDSA
certificates are not supported in 802.1AR-2018; this is for future
work).
This guide was originally developed with openSSL 1.1.1; it is updated
using openSSL 3.0.9 on Fedora 38 and creates PEM-based certificates.
It closely follows [ecdsa-pki]. Current updates follow some lessons
learned in developing [drip-dki]
Previous versions had multiple openssl config files. This version
has a single config file to support all the openssl commands used
herein.
2. Terms and Definitions
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2.1. Requirements Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.2. Notations
This section will contain notations
2.3. Definitions
There are no draft specific definitions at this time
3. Comparing ECDSA and EdDSA certificates
There are two differences between ECDSA and EdDSA certificates that
impact the use of openSSL. There are no options with EdDSA, and thus
the pkeyopt variable is not used.
Likewise there are no hash options. The hashes used by EdDSA are
preset and not selectable. As such, none of the hash options should
be needed.
It should be noted here that ED25519 certificates can be ~100 bytes
smaller than corresponding ECDSA certificates not using ECDSA point-
compression. This size difference may be critical in some devices
and communication technologies. ED448 certificates are similar in
size with ECDSA p256 certificates yet with a stronger security claim.
4. The Basic PKI feature set
A basic PKI has two levels of hierarchy: Root and Intermediate. The
Root level has the greatest risk, and is the least used. It only
signs the Intermediate level signing certificate. As such, once the
Root level is created and signs the Intermediate level certificate it
can be locked up. In fact, the Root level could exist completely on
a uSD boot card for an ARM small computer like a RaspberryPi. A copy
of this card can be made and securely stored in a different location.
The Root level contains the Root certificate private key, a database
of all root signed certificates, and the public root certificate. It
can also contain the Intermediate level public certificate and a Root
level CRL.
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The Intermediate level contains the Intermediate certificate private
key, the public certificate, a database of all its signed
certificates, the certificate trust chain, and Intermediate level
CRL. It can also contain the End Entity public certificates. The
private key file needs to be keep securely. For example as with the
Root level, a mSD image for an ARM computer could contain the
complete Intermediate level. This image is kept offline. The End
Entity CSR is copied to it, signed, and then the signed certificate
and updated database are moved to the public image that lacks the
private key.
For a simple test PKI, all files can be kept on a single system that
is managed by the tester.
End Entities create a key pair and a Certificate Signing Request
(CSR). The private key is stored securely. The CSR is delivered to
the Intermediate level which uses the CSR to create the End Entity
certificate. This certificate, along with the trust chain back to
the root, is then returned to the End Entity.
There is more to a PKI, but this suffices for most development and
testing needs.
5. Getting started and the Root level
This guide was originally developed on a Fedora 29-beta armv7hl
system (Cubieboard2 SoC). It should work on most Linux and similar
systems that support openSSL 1.1.1. Current work has been on with
openSSL 3.0.9 on Fedora 38. All work was done in a terminal window
with extensive "cutting and pasting" from this draft guide into the
terminal window. Users of this guide may find different behaviors
based on their system.
The sourcecode blocks are now structured to work with Carsten
Bormann's kramdown-rfc-extract-sourcecode script. At the time of
publication, this script was part of the gem kramdown-rfc collection.
Place the xml for this document into a directory and run:
| kramdown-rfc-extract-sourcecode thisdraft.xml --dir=scriptdir
This will create all the scripts below into directory scriptdir/bash
and config files into scriptdir/conf. Edit these to suit your needs
then proceed.
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5.1. Setting up the Environment
The first step is to create the PKI environment. Modify the
variables in setup1.sh to suit your needs.
export dir=/root/ca
export cadir=/root/ca
export format=pem
export algorithm=ed25519 # or ed448
# or for ECDSA with P-256:
# export algorithm="ec -pkeyopt ec_paramgen_curve:prime256v1"
mkdir $dir
cp scriptdir/conf/openssl.cnf $dir
cd $dir
mkdir certs crl csr newcerts private
chmod 700 private
touch index.txt
touch serial
sn=8
countryName="/C=US"
stateOrProvinceName="/ST=MI"
localityName="/L=Oak Park"
organizationName="/O=HTT Consulting"
#organizationalUnitName="/OU="
organizationalUnitName=
commonName="/CN=Root CA"
DN=$countryName$stateOrProvinceName$localityName
DN=$DN$organizationName$organizationalUnitName$commonName
echo $DN
export subjectAltName=email:postmaster@htt-consult.com
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where:
dir : Directory for certificate files
cadir : Directory for Root certificate files
format : File encoding: PEM or DER
At this time only PEM works
algorithm : EC algorithm used in certificates
sn : Serial Number length in bytes
For a public CA the range is 8 to 20
DN : Distinguished Name
Policy is LOOSE; Recommended at least
providing Common Name
The DN and SAN fields are examples. Change them to appropriate
values. If you leave one blank, it will be left out of the
Certificate. "OU" above is an example of an empty DN object.
| Make sure that $dir/openssl.cnf from the contents in Appendix A
| exists. setup1.sh should have copied it into your CA directory.
5.2. Create the Root Certificate
Next is the rootcert.sh script with the openssl commands to create
the Root certificate keypair, and the Root certificate. Included are
commands to view the file contents.
Environment variables are used to provide considerable flexibility in
the certificate contents. Many of these variables need to be
customized; sample values are provided. Validity notBefore and
notAfter days variables are used, rather that life in days. This is
not supported in the standard self-sign root certificate creation, so
a "throw-away" self-signed certificate is created first which is used
to sign a certificate with the same key and proper validity dates
which is then the root certificate.
It is not uncommon to get warning messages in "openssl ca" commands
on not including some value it expects. For example a warning of not
having "default_days", as we are using actual validity dates. These
can be ignored.
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OpenSSL does not allow empty variables in the config file. So in the
example below, certextkeyusage is empty. There are a few req_ext
sections (e.g. req_ext_bkes, bke, bks, and bk) to cover the more
common sets of extensions used. If a different set is needed, add it
to the config file.
# Create passworded keypair file
export encryptkey=""
#export encryptkey="-aes256" # use to password protect private key
openssl genpkey $encryptkey -algorithm $algorithm\
-outform $format -out $dir/private/ca.key.$format
# For ECDSA point-compression
#openssl ec -conv_form compressed \
# -in $dir/private/ca.key.$format\
# -out $dir/private/ca.key.$format
chmod 400 $dir/private/ca.key.$format
openssl pkey -inform $format -in $dir/private/ca.key.$format\
-text -noout
# Create Self-signed Throw-away Certificate file
export signprv="ca"
export signcert="cabase"
export basicConstraints="critical, CA:true"
export certkeyusage="critical, keyCertSign"
export certextkeyusage=""
export hwType="place holder" # all ENV in config must
export hwSerialNum="place holder" # be define
export startdate=20230801000000Z # YYYYMMDDHHMMSSZ
export enddate=20430731000000Z # YYYYMMDDHHMMSSZ
openssl req -config $dir/openssl.cnf\
-set_serial 0x$(openssl rand -hex $sn)\
-keyform $format -outform $format\
-key $dir/private/ca.key.$format -subj "$DN"\
-new -x509 -extensions v3_ca\
-out $dir/certs/$signcert.cert.$format
openssl x509 -in $dir/certs/$signcert.cert.$format\
-inform $format -text -noout
openssl x509 -purpose -inform $format\
-in $dir/certs/$signcert.cert.$format -inform $format
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# Create Self-signed Root Certificate file
openssl req -config $dir/openssl.cnf -reqexts req_ext_bk\
-key $dir/private/ca.key.$format \
-subj "$DN" -new -out $dir/csr/ca.csr.$format
openssl req -text -noout -verify\
-in $dir/csr/ca.csr.$format
openssl rand -hex $sn > $dir/serial # hex 8 is minimum, 20 is maximum
openssl ca -config $dir/openssl.cnf\
-extensions v3_ca -notext \
-in $dir/csr/ca.csr.$format\
-out $dir/certs/ca.cert.$format
chmod 444 $dir/certs/ca.cert.$format
openssl x509 -inform $format -in $dir/certs/ca.cert.$format\
-text -noout
openssl x509 -purpose -inform $format\
-in $dir/certs/ca.cert.$format -inform $format
openssl x509 -in $dir/certs/ca.cert.$format\
-out $dir/certs/ca.cert.der -outform der
6. The Intermediate level
6.1. Setting up the Intermediate Certificate Environment
The next part is to create the Intermediate PKI environment. Modify
the variables in intermediate_setup.sh to suit your needs. In
particular, set the variables for CRL and/or OCSP support.
export dir=$cadir/intermediate
mkdir $dir
cp openssl.cnf $dir
cd $dir
mkdir certs crl csr newcerts private
chmod 700 private
touch index.txt
sn=8 # hex 8 is minimum, 20 is maximum
echo 1000 > $dir/crlnumber
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# cd $dir
export crlDP=
# For CRL support use, uncomment these:
#crl=intermediate.crl.pem
#crlurl=www.htt-consult.com/pki/$crl
#export crlDP="URI:http://$crlurl"
export default_crl_days=30
export ocspIAI=
# For OCSP support use, uncomment these:
#ocspurl=ocsp.htt-consult.com
#export ocspIAI="OCSP;URI:http://$ocspurl"
export signprv="ca"
export signcert="ca"
export basicConstraints="critical, CA:true, pathlen:0"
export certkeyusage="critical, cRLSign, keyCertSign"
export certextkeyusage=""
commonName="/CN=Signing CA"
DN=$countryName$stateOrProvinceName$localityName$organizationName
DN=$DN$organizationalUnitName$commonName
echo $DN
| The Intermediate level CA now uses the same openssl config file as
| the root. The intermediate_setup.sh should have copied it from
| the main directory into the Intermediate.
6.2. Create the Intermediate Certificate
Here are the openssl commands to create the Intermediate certificate
keypair, Intermediate certificate signed request (CSR), and the
Intermediate certificate. Included are commands to view the file
contents.
# Create passworded keypair file
export encryptkey=""
#export encryptkey="-aes256" # use to password protect private key
openssl genpkey $encryptkey -algorithm $algorithm\
-outform $format -out $dir/private/intermediate.key.$format
# For ECDSA point-compression
#openssl ec -conv_form compressed \
# -in $dir/private/intermediate.key.$format\
# -out $dir/private/intermediate.key.$format
chmod 400 $dir/private/intermediate.key.$format
openssl pkey -inform $format\
-in $dir/private/intermediate.key.$format -text -noout
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# Create the CSR
openssl req -config $cadir/openssl.cnf -reqexts req_ext_bk\
-key $dir/private/intermediate.key.$format \
-keyform $format -outform $format -subj "$DN" -new\
-out $dir/csr/intermediate.csr.$format
openssl req -text -noout -verify -inform $format\
-in $dir/csr/intermediate.csr.$format
# Create Intermediate Certificate file
export startdate=230801000000Z # YYMMDDHHMMSSZ
export enddate=20340731000000Z # YYYYMMDDHHMMSSZ
openssl rand -hex $sn > $dir/serial # hex 8 is minimum, 20 is maximum
# Note 'openssl ca' does not support DER format
openssl ca -config $cadir/openssl.cnf\
-extensions v3_intermediate_ca -notext \
-in $dir/csr/intermediate.csr.$format\
-out $dir/certs/intermediate.cert.pem
chmod 444 $dir/certs/intermediate.cert.$format
openssl verify -CAfile $cadir/certs/ca.cert.$format\
$dir/certs/intermediate.cert.$format
openssl x509 -noout -text -in $dir/certs/intermediate.cert.$format
openssl x509 -in $dir/certs/intermediate.cert.$format\
-out $dir/certs/intermediate.cert.der -outform der
# Create the certificate chain file
cat $dir/certs/intermediate.cert.$format\
$cadir/certs/ca.cert.$format > $dir/certs/ca-chain.cert.$format
chmod 444 $dir/certs/ca-chain.cert.$format
6.3. Create a Server EE Certificate
Here are the openssl commands to create a Server End Entity
certificate keypair, Server certificate signed request (CSR), and the
Server certificate. Included are commands to view the file contents.
If EE certificates are created at a different time than the
Intermediate signing certificate, care needs to be taken that all
variables are properly reset.
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export cadir=$cadir/intermediate
commonName="/CN=Web Services"
DN=$countryName$stateOrProvinceName$localityName
DN=$DN$organizationName$organizationalUnitName$commonName
echo $DN
serverfqdn=www.example.com
emailaddr=postmaster@htt-consult.com
export subjectAltName="DNS:$serverfqdn, email:$emailaddr"
echo $subjectAltName
export signprv="intermediate"
export signcert="intermediate"
export basicConstraints="CA:FALSE"
export certkeyusage="critical, digitalSignature, keyEncipherment"
export certextkeyusage="serverAuth"
export encryptkey=""
#export encryptkey="-aes256" # use to password protect private key
openssl genpkey $encryptkey -algorithm $algorithm\
-out $dir/private/$serverfqdn.key.$format
# For ECDSA point-compression
#openssl ec -conv_form compressed \
# -in $dir/private/$serverfqdn.key.$format\
# -out $dir/private/$serverfqdn.key.$format
chmod 400 $dir/private/$serverfqdn.key.$format
openssl pkey -in $dir/private/$serverfqdn.key.$format -text -noout
openssl req -config $cadir/openssl.cnf -reqexts req_ext_bkes\
-key $dir/private/$serverfqdn.key.$format \
-subj "$DN" -new -out $dir/csr/$serverfqdn.csr.$format
openssl req -text -noout -verify -in $dir/csr/$serverfqdn.csr.$format
export startdate=230801000000Z # YYMMDDHHMMSSZ
export enddate=240731000000Z # YYMMDDHHMMSSZ
openssl rand -hex $sn > $dir/serial # hex 8 is minimum, 20 is maximum
# Note 'openssl ca' does not support DER format
openssl ca -config $cadir/openssl.cnf\
-extensions server_cert -notext \
-in $dir/csr/$serverfqdn.csr.$format\
-out $dir/certs/$serverfqdn.cert.$format
chmod 444 $dir/certs/$serverfqdn.cert.$format
openssl verify -CAfile $dir/certs/ca-chain.cert.$format\
$dir/certs/$serverfqdn.cert.$format
openssl x509 -noout -text -in $dir/certs/$serverfqdn.cert.$format
openssl x509 -in $dir/certs/$serverfqdn.cert.$format\
-out $dir/certs/$serverfqdn.cert.der -outform der
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6.4. Create a Client EE Certificate
Here are the openssl commands to create a Client End Entity
certificate keypair, Client certificate signed request (CSR), and the
Client certificate. Included are commands to view the file contents.
For a Client certificate with "no" subject and only a subjectAltName,
set the variable DN to "/". Also the subjectAltName MUST be marked
"critical".
commonName=
UserID="/UID=rgm"
DN=$countryName$stateOrProvinceName$localityName
DN=$DN$organizationName$organizationalUnitName$commonName$UserID
echo $DN
clientemail=rgm@example.com
export subjectAltName="email:$clientemail"
echo $subjectAltName
export basicConstraints="CA:FALSE"
export certkeyusage="critical, digitalSignature, keyEncipherment"
export certextkeyusage=""
export encryptkey=""
#export encryptkey="-aes256" # use to password protect private key
openssl genpkey $encryptkey -algorithm $algorithm\
-out $dir/private/$clientemail.key.$format
# For ECDSA point-compression
#openssl ec -conv_form compressed \
# -in $dir/private/$clientemail.key.$format\
# -out $dir/private/$clientemail.key.$format
chmod 400 $dir/private/$clientemail.key.$format
openssl pkey -in $dir/private/$clientemail.key.$format -text -noout
openssl req -config $dir/openssl.cnf -reqexts req_ext_bks\
-key $dir/private/$clientemail.key.$format \
-subj "$DN" -new -out $dir/csr/$clientemail.csr.$format
openssl req -text -noout -verify\
-in $dir/csr/$clientemail.csr.$format
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export startdate=230801000000Z # YYMMDDHHMMSSZ
export enddate=240731000000Z # YYMMDDHHMMSSZ
openssl rand -hex $sn > $dir/serial # hex 8 is minimum, 20 is maximum
# Note 'openssl ca' does not support DER format
openssl ca -config $dir/openssl.cnf\
-extensions usr_cert -notext \
-in $dir/csr/$clientemail.csr.$format\
-out $dir/certs/$clientemail.cert.$format
chmod 444 $dir/certs/$clientemail.cert.$format
openssl verify -CAfile $dir/certs/ca-chain.cert.$format\
$dir/certs/$clientemail.cert.$format
openssl x509 -noout -text -in $dir/certs/$clientemail.cert.$format
openssl x509 -in $dir/certs/$clientemail.cert.$format\
-out $dir/certs/$clientemail.cert.der -outform der
7. The 802.1AR Intermediate level
7.1. Setting up the 802.1AR Intermediate Certificate Environment
There is no longer a need for a special 802.1AR Intermediate
Certificate CA. The regular Intermediate Certificate CA may be used
for 802.1AR iDevID certificates. A special CA may be set up by
following the steps outlined in Section 6, but into a separate
intermediate8021AR directory.
The difference with 802.1AR device certificates may be in including
in the subject the device serial number. 802.1AR iDevID certificates
MUST have an afterDate of forever and a specific subjectAltName with
the hardwareModuleName OID [RFC4108]. Details for these follow.
7.2. Create an 802.1AR iDevID Certificate
Here are the openssl commands to create a 802.1AR iDevID certificate
keypair, iDevID certificate signed request (CSR), and the iDevID
certificate. Included are commands to view the file contents.
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DevID=Wt1234
countryName=
stateOrProvinceName=
localityName=
organizationName="/O=HTT Consulting"
organizationalUnitName="/OU=Devices"
commonName=
serialNumber="/serialNumber=$DevID"
DN=$countryName$stateOrProvinceName$localityName
DN=$DN$organizationName$organizationalUnitName$commonName
DN=$DN$serialNumber
echo $DN
# hwType is OID for HTT Consulting, devices, sensor widgets
export hwType=1.3.6.1.4.1.6715.10.1
export hwSerialNum=01020304 # Some hex
export subjectAltName="otherName:1.3.6.1.5.5.7.8.4;SEQ:hmodname"
echo $hwType - $hwSerialNum
openssl genpkey -algorithm $algorithm\
-out $dir/private/$DevID.key.$format
# For ECDSA point-compression
#openssl ec -conv_form compressed \
# -in $dir/private/$DevID.key.$format\
# -out $dir/private/$DevID.key.$format
chmod 400 $dir/private/$DevID.key.$format
openssl pkey -in $dir/private/$DevID.key.$format -text -noout
openssl req -config $dir/openssl.cnf -reqexts req_ext_8021AR \
-key $dir/private/$DevID.key.$format \
-subj "$DN" -new -out $dir/csr/$DevID.csr.$format
openssl req -text -noout -verify\
-in $dir/csr/$DevID.csr.$format
openssl asn1parse -i -in $dir/csr/$DevID.csr.pem
# offset of start of hardwareModuleName and use that in place of 169
openssl asn1parse -i -strparse 169 -in $dir/csr/$DevID.csr.pem
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export startdate=230801000000Z # YYMMDDHHMMSSZ
export enddate=99991231235959Z # per IEEE 802.1AR
openssl rand -hex $sn > $dir/serial # hex 8 is minimum, 20 is maximum
# Note 'openssl ca' does not support DER format
openssl ca -config $dir/openssl.cnf\
-extensions 8021ar_idevid -notext \
-in $dir/csr/$DevID.csr.$format\
-out $dir/certs/$DevID.cert.$format
chmod 444 $dir/certs/$DevID.cert.$format
openssl verify -CAfile $dir/certs/ca-chain.cert.$format\
$dir/certs/$DevID.cert.$format
openssl x509 -noout -text -in $dir/certs/$DevID.cert.$format
openssl asn1parse -i -in $dir/certs/$DevID.cert.pem
# offset of start of hardwareModuleName and use that in place of 367
openssl asn1parse -i -strparse 367 -in $dir/certs/$DevID.cert.pem
openssl x509 -in $dir/certs/$DevID.cert.$format\
-out $dir/certs/$DevID.cert.der -outform der
8. Setting up a CRL for an Intermediate CA
This part provides CRL support to an Intermediate CA. In this memo
it applies to both Intermediate CAs. Set the crlDistributionPoints
as provided via the environment variables.
8.1. Create (or recreate) the CRL
It is simple to create the CRL. The CRL consists of the certificates
flagged with an R (Revoked) in index.txt:
# Select which Intermediate level
intermediate=intermediate
#intermediate=8021ARintermediate
dir=$cadir/$intermediate
crl=$intermediate.crl.pem
cd $dir
# Create CRL file
openssl ca -config $dir/openssl.cnf \
-gencrl -out $dir/crl/$crl
chmod 444 $dir/crl/$crl
openssl crl -in $dir/crl/$crl -noout -text
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8.2. Revoke a Certificate
Revoking a certificate is a two step process. First identify the
target certificate, examples are listed below. Revoke it then
publish a new CRL.
targetcert=$serverfqdn
#targetcert=$clientemail
#targetcert=$DevID
openssl ca -config $dir/openssl.cnf\
-revoke $dir/certs/$targetcert.cert.$format
Recreate the CRL using Section 8.1.
9. Setting up OCSP for an Intermediate CA
This part provides OCSP support to an Intermediate CA. In this memo
it applies to both Intermediate CAs. Set the authorityInfoAccess as
provided via the environment variables.
9.1. Create the OCSP Certificate
OCSP needs a signing certificate. This certificate must be signed by
the CA that signed the certificate being checked. The steps to
create this certificate is the similar to a Server certificate for
the CA:
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# Select which Intermediate level
intermediate=intermediate
#intermediate=8021ARintermediate
# Optionally, password encrypt key pair
encryptkey=
#encryptkey=-aes256
# Create the key pair in Intermediate level $intermediate
cd $dir
openssl genpkey -algorithm $algorithm\
$encryptkey -out $dir/private/$ocspurl.key.$format
# For ECDSA point-compression
#openssl ec -conv_form compressed \
# -in $dir/private/$ocspurl.key.$format\
# -out $dir/private/$ocspurl.key.$format
chmod 400 $dir/private/$ocspurl.key.$format
openssl pkey -in $dir/private/$ocspurl.key.$format -text -noout
# Create CSR
commonName="/CN=ocsp"
DN=$countryName$stateOrProvinceName$localityName
DN=$DN$organizationName$organizationalUnitName$commonName
echo $DN
emailaddr=postmaster@htt-consult.com
export subjectAltName="DNS:$ocspurl, email:$emailaddr"
echo $subjectAltName
openssl req -config $dir/openssl.cnf -reqexts req_ext_bks \
-key $dir/private/$ocspurl.key.$format \
-subj "$DN" -new -out $dir/csr/$ocspurl.csr.$format
openssl req -text -noout -verify -in $dir/csr/$ocspurl.csr.$format
# Create Certificate
export startdate=230801000000Z # YYMMDDHHMMSSZ
export enddate=99991231235959Z # per IEEE 802.1AR
openssl rand -hex $sn > $dir/serial # hex 8 is minimum, 20 is maximum
# Note 'openssl ca' does not support DER format
openssl ca -config $dir/openssl.cnf\
-extensions ocsp -notext \
-in $dir/csr/$ocspurl.csr.$format\
-out $dir/certs/$ocspurl.cert.$format
chmod 444 $dir/certs/$ocspurl.cert.$format
openssl verify -CAfile $dir/certs/ca-chain.cert.$format\
$dir/certs/$ocspurl.cert.$format
openssl x509 -noout -text -in $dir/certs/$ocspurl.cert.$format
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9.2. Revoke a Certificate
Revoke the certificate as in Section 8.2. The OCSP responder SHOULD
detect the flag change in index.txt and, when queried respond
appropriately.
9.3. Testing OCSP with Openssl
OpenSSL provides a simple OCSP service that can be used to test the
OCSP certificate and revocation process (Note that this only reads
the index.txt to get the certificate status at startup).
In a terminal window, set variables dir and ocspurl (examples below),
then run the simple OCSP service:
dir=/root/ca/intermediate
ocspurl=ocsp.htt-consult.com
openssl ocsp -port 2560 -text\
-index $dir/index.txt \
-CA $dir/certs/ca-chain.cert.pem \
-rkey $dir/private/$ocspurl.key.pem \
-rsigner $dir/certs/$ocspurl.cert.pem \
-nrequest 1
In another window, test out a certificate status with:
targetcert=$serverfqdn
#targetcert=$clientemail
#targetcert=$DevID
openssl ocsp -CAfile $dir/certs/ca-chain.cert.pem \
-url http://127.0.0.1:2560 -resp_text\
-issuer $dir/certs/intermediate.cert.pem \
-cert $dir/certs/$targetcert.cert.pem
Revoke the certificate, Section 8.2, restart the test Responder again
as above, then check the certificate status.
10. Footnotes
Creating this document was a real education in the state of openSSL,
X.509 certificate guidance, and just general level of certificate
awareness. Here are a few short notes.
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10.1. Certificate Serial Number
The certificate serial number's role is to provide yet another way to
maintain uniqueness of certificates within a PKI as well as a way to
index them in a data store. It has taken on other roles, most
notably as a defense.
The CABForum guideline for a public CA is for the serial number to be
a random number at least 8 octets long and no longer than 20 bytes.
Appendix B of [RFC5280] states that "CAs MUST force the serialNumber
to be a non-negative integer, that is, the sign bit in the DER
encoding of the INTEGER value MUST be zero".
By default, openssl makes self-signed certificates with 8 octet
serial numbers. This guide uses openssl's RAND function to generate
a random value and pipe it into the serial file which is used in by
the config file. This number MAY have the first bit as a ONE; the
DER encoding rules prepend such numbers with 0x00. Thus increasing
the actual certificate size by a byte.
An 8-byte serial number with the first bit of zero can be generated
by limiting the random generation to less than 2^63:
printf "%016X\n" $(shuf -rn 1 -i 1-9223372036854775807 \
--random-source=/dev/urandom) > $dir/serial
# or
printf "%016X\n" $((16#$(openssl rand -hex 8) & 0x7fffffffffffffff))\
> $dir/serial
A private CA need not follow the CABForum rules and can use anything
number for the serial number. For example, the root CA (which has no
security risks mitigated by using a random value) could use '1' as
its serial number. Intermediate and End Entity certificate serial
numbers can also be of any value if a strong hash, like SHA256 used
here. A value of 4 for ns would provide a sufficient population so
that a CA of 10,000 EE certificates will have only a 1.2% probability
of a collision. For only 1,000 certificates the probability drops to
0.012%.
The following was proposed on the openssl-user list as an alternative
to using the RAND function:
Keep k bits (k/8 octets) long serial numbers for all your
certificates, chose a block cipher operating on blocks of k bits, and
operate this block cipher in CTR mode, with a proper secret key and
secret starting counter. That way, no collision detection is
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necessary, you’ll be able to generate 2^(k/2) unique k bits longs
serial numbers (in fact, you can generate 2^k unique serial numbers,
but after 2^(k/2) you lose some security guarantees).
With 3DES, k=64, and with AES, k=128.
10.2. Some OpenSSL config file limitations
There is a bit of inconsistency in how different parts and fields in
the config file are used. Environment variables can only be used as
values. Some fields can have null values, others cannot. The lack
of allowing null fields means a script cannot feed in an environment
variable with value null. In such a case, the field has to be
removed from the config file.
The expectation is each CA within a PKI has its own config file,
customized to the certificates supported by that CA.
10.3. subjectAltName support now works
Older versions of openSSL had limitations in support for
subjectAltName (SAN). This is no longer the case. This document
sets up the SAN in the config file. Alternatively, the "-addext"
option can be used directly in the command line.
10.4. Certificates with only subjectAltName
In Section 4.2.1.6 of [RFC5280]: if the only subject identity in the
certificate is in subjectAltName, then Subject MUST be empty and
subjectAltName MUST be marked as critical.
This can be achieved with the variable DN=/ and subjectAltName
(example given):
DN=/
export subjectAltName=critical,email:postmaster@htt-consult.com
10.5. DER support, or lack thereof
The long, hard-fought battle with openssl to create a full DER PKI
failed. There is no facility to create a DER certificate from a DER
CSR. It just is not there in the 'openssl ca' command. Even the
'openssl x509 -req' command cannot do this for a simple certificate.
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Further, there is no 'hack' for making a certificate chain as there
is with PEM. With PEM a simple concatenation of the certificates
create a usable certificate chain. For DER, some recommend using
PKCS#7 [RFC2315], where others point out that this format is poorly
support 'in the field', whereas PKCS#12 [RFC7292] works for them.
Finally, openssl does support converting a PEM certificate to DER:
openssl x509 -outform der -in certificate.pem -out certificate.der
This should also work for the keypair. However, in a highly
constrained device it may make more sense to just store the raw
keypair in the device's very limited secure storage.
11. IANA Considerations
TBD. May be nothing for IANA.
12. Security Considerations
12.1. Adequate Randomness
Creating certificates takes a lot of random numbers. A good source
of random numbers is critical. Studies [WeakKeys] have found
excessive amount of certificates, all with the same keys due to bad
randomness on the generating systems. The amount of entropy
available for these random numbers can be tested. On Fedora/Centos
and most Linux systems use:
cat /proc/sys/kernel/random/entropy_avail
If the value is low (below 1000) check your system's randomness
source. Is rng-tools installed? Consider adding an entropy
collection service like haveged from issihosts.com/haveged.
12.2. Key pair Theft
During the certificate creation, particularly during keypair
generation, the files are vulnerable to theft. This can be mitigate
using umask. Before using openssl, set umask:
restore_mask=$(umask -p)
umask 077
Afterwards, restore it with:
$restore_mask
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or just close the shell that was used, and start a new one. (The -p
option to umask is a bash-ism)
There is nothing in these recipes that requires super-user on the
system creating the certificates. Provided that adequate randomness
is available, a virtual machine or container is entirely appropriate.
Containers tend to have better access to randomness than virtual
machines.
The scripts and configuration files and in particular, private keys,
may be kept offline on a USB key for instance, and loaded when
needed.
The OCSP server needs to be online and available to all clients that
will use the certificates. This may mean available on the Internet.
A firewall can protect the OCSP server, and port-forwards and/or ACL
rules can restrict access to just the OCSP port. OCSP artifacts are
signed by a key designed for that purpose only so do not require that
the associated CA key be available online.
Generating new CRLs, however, requires that the CA signing key be
online, which is one of the reasons for creating an intermediate CA.
13. Acknowledgments
This work was jump started by the excellent RSA pki guide by Jamie
Nguyen. The openssl-user mailing list, with its many supportive
experts; in particular: Rich Salz, Jakob Bolm, Viktor Dukhovni, and
Erwann Abalea, was of immense help as was the openssl man pages
website.
Finally, "Professor Google" was always ready to point to answers to
questions like: "openssl subjectAltName on the command line". And
the Professor, it seems, never tires of answering even trivial
questions.
The openssl-user mailing list, with its many supportive experts, was
of immense help in the nuance differences between ECDSA and EdDSA.
The sourcecode blocks are structured to work with Carsten Bormann's
kramdown-rfc-extract-sourcecode script. At the time of publication,
this script was part of the gem kramdown-rfc collection.
14. References
14.1. Normative References
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
14.2. Informative References
[drip-dki] Moskowitz, R. and S. W. Card, "The DRIP DET public Key
Infrastructure", Work in Progress, Internet-Draft, draft-
moskowitz-drip-dki-09, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-moskowitz-
drip-dki-09>.
[ecdsa-pki]
Moskowitz, R., Birkholz, H., Xia, L., and M. Richardson,
"Guide for building an ECC pki", Work in Progress,
Internet-Draft, draft-moskowitz-ecdsa-pki-10, 31 January
2021, <https://datatracker.ietf.org/doc/html/draft-
moskowitz-ecdsa-pki-10>.
[IEEE 802.1AR]
IEEE, "IEEE Standard for Local and Metropolitan Area
Networks - Secure Device Identity",
DOI 10.1109/ieeestd.2018.8423794, 31 July 2018,
<https://doi.org/10.1109/ieeestd.2018.8423794>.
[NIST.FIPS.186-5]
Chen, L., Moody, D., Regenscheid, A., Robinson, A., and
National Institute of Standards and Technology (U.S.),
"Digital Signature Standard (DSS)",
DOI 10.6028/nist.fips.186-5, 3 February 2023,
<https://doi.org/10.6028/nist.fips.186-5>.
[RFC2315] Kaliski, B., "PKCS #7: Cryptographic Message Syntax
Version 1.5", RFC 2315, DOI 10.17487/RFC2315, March 1998,
<https://www.rfc-editor.org/info/rfc2315>.
[RFC4108] Housley, R., "Using Cryptographic Message Syntax (CMS) to
Protect Firmware Packages", RFC 4108,
DOI 10.17487/RFC4108, August 2005,
<https://www.rfc-editor.org/info/rfc4108>.
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[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC7292] Moriarty, K., Ed., Nystrom, M., Parkinson, S., Rusch, A.,
and M. Scott, "PKCS #12: Personal Information Exchange
Syntax v1.1", RFC 7292, DOI 10.17487/RFC7292, July 2014,
<https://www.rfc-editor.org/info/rfc7292>.
[RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
Signature Algorithm (EdDSA)", RFC 8032,
DOI 10.17487/RFC8032, January 2017,
<https://www.rfc-editor.org/info/rfc8032>.
[WeakKeys] Heninger, N.H., Durumeric, Z.D., Wustrow, E.W., and J.A.H.
Halderman, "Detection of Widespread Weak Keys in Network
Devices", July 2011,
<https://www.usenix.org/system/files/conference/
usenixsecurity12/sec12-final228.pdf>.
Appendix A. OpenSSL config file
The following is the openssl.cnf file contents
# OpenSSL CA configuration file.
# Copy to `$dir/openssl.cnf`.
[ ca ]
# `man ca`
default_ca = CA_default
[ CA_default ]
# Directory and file locations.
dir = $ENV::dir
cadir = $ENV::cadir
format = $ENV::format
signprv = $ENV::signprv
signcert = $ENV::signcert
certkeyusage = $ENV::certkeyusage
certextkeyusage = $ENV::certextkeyusage
basicConstraints = $ENV::basicConstraints
certs = $dir/certs
crl_dir = $dir/crl
new_certs_dir = $dir/newcerts
database = $dir/index.txt
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serial = $dir/serial
RANDFILE = $dir/private/.rand
# The signing key and signing certificate.
private_key = $cadir/private/$signprv.key.$format
certificate = $cadir/certs/$signcert.cert.$format
# For certificate revocation lists.
crlnumber = $dir/crlnumber
crl = $dir/crl/ca.crl.pem
crl_extensions = crl_ext
default_crl_days = 30
# SHA-1 is deprecated, so use SHA-2 instead.
default_md = sha256
name_opt = ca_default
cert_opt = ca_default
default_startdate = $ENV::startdate
default_enddate = $ENV::enddate
preserve = no
policy = policy_loose
copy_extensions = copy
[ policy_loose ]
# Allow the intermediate CA to sign a more
# diverse range of certificates.
# See the POLICY FORMAT section of the `ca` man page.
countryName = optional
stateOrProvinceName = optional
localityName = optional
organizationName = optional
organizationalUnitName = optional
commonName = optional
UID = optional
serialNumber = optional
[ req ]
# Options for the `req` tool (`man req`).
distinguished_name = req_distinguished_name
string_mask = utf8only
#req_extensions = req_ext
default_crl_days = 30
# SHA-1 is deprecated, so use SHA-2 instead.
default_md = sha256
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# Extension to add when the -x509 option is used.
x509_extensions = v3_ca
[ req_distinguished_name ]
# See <https://en.wikipedia.org/wiki/Certificate_signing_request>.
#countryName = Country Name (2 letter code)
#stateOrProvinceName = State or Province Name
#localityName = Locality Name
#0.organizationName = Organization Name
#organizationalUnitName = Organizational Unit Name
commonName = Common Name
[ req_ext ]
[ req_ext_bkes ]
basicConstraints = $ENV::basicConstraints
keyUsage = $ENV::certkeyusage
extendedKeyUsage = $ENV::certextkeyusage
subjectAltName = $ENV::subjectAltName
[ req_ext_bke ]
basicConstraints = $ENV::basicConstraints
keyUsage = $ENV::certkeyusage
extendedKeyUsage = $ENV::certextkeyusage
[ req_ext_bks ]
basicConstraints = $ENV::basicConstraints
keyUsage = $ENV::certkeyusage
subjectAltName = $ENV::subjectAltName
[ req_ext_bk ]
basicConstraints = $ENV::basicConstraints
keyUsage = $ENV::certkeyusage
[ req_ext_8021AR ]
basicConstraints = $ENV::basicConstraints
keyUsage = $ENV::certkeyusage
subjectAltName = $ENV::subjectAltName
[ hmodname ]
hwType = OID:$ENV::hwType
hwSerialNum = FORMAT:HEX,OCT:$ENV::hwSerialNum
[ v3_ca ]
# Extensions for a typical CA (`man x509v3_config`).
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always
basicConstraints = $ENV::basicConstraints
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keyUsage = $ENV::certkeyusage
[ v3_intermediate_ca ]
# Extensions for a typical intermediate CA (`man x509v3_config`).
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always
# basicConstraints = $ENV::basicConstraints
# keyUsage = $ENV::certkeyusage
# subjectAltName = $ENV::subjectAltName
[ usr_cert ]
# Extensions for client certificates (`man x509v3_config`).
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always
# uncomment the following if the ENV variables set
# crlDistributionPoints = $ENV::crlDP
# authorityInfoAccess = $ENV::ocspIAI
[ usr_req ]
# Extensions for client certificates (`man x509v3_config`).
subjectAltName = critical, $ENV::subjectAltName
[ server_cert ]
# Extensions for server certificates (`man x509v3_config`).
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always
# uncomment the following if the ENV variables set
# crlDistributionPoints = $ENV::crlDP
# authorityInfoAccess = $ENV::ocspIAI
[ 8021ar_idevid ]
# Extensions for IEEE 802.1AR iDevID
# certificates (`man x509v3_config`).
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always
# uncomment the following if the ENV variables set
# crlDistributionPoints = $ENV::crlDP
# authorityInfoAccess = $ENV::ocspIAI
[ crl_ext ]
# Extension for CRLs (`man x509v3_config`).
authorityKeyIdentifier=keyid:always
[ ocsp ]
# Extension for OCSP signing certificates (`man ocsp`).
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always
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Authors' Addresses
Robert Moskowitz
HTT Consulting
Oak Park
Email: rgm@labs.htt-consult.com
Henk Birkholz
Fraunhofer SIT
Rheinstrasse 75
64295 Darmstadt
Germany
Email: henk.birkholz@sit.fraunhofer.de
Michael C. Richardson
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
URI: http://www.sandelman.ca/
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