Table of Contents

Setup

Since this tutorial focuses on OpenSSL, it is assumed that the reader is running a UNIX-like environment and is familiar with the terminal. In other words, if you are running Linux, OS X, or UNIX, then you're good to go. If you are running Windows, you can use Cygwin to "get that Linux feeling on Windows."

OpenSSL Installation

Please follow the directions below as they pertain to your operating system:

Windows.   During Cygwin installation, select Net » openssl.

OS X.   You already have OpenSSL. Hooray!

GNU/Linux and UNIX.   Most distributions include OpenSSL already. If which openssl outputs nothing in your terminal, please use your distro's package manager to install the openssl package, or download and compile it yourself.

Preliminary Directory Structure

Create a directory that will serve as the base directory for your certificate authority. OpenSSL will use this directory to handle keys, certificates, certificate signing requests, certificate revocation lists, etc.

$ mkdir MyAwesomeCA
$ cd MyAwesomeCA

Next, create the base directory structure for the CA "database". After this, OpenSSL will handle most of these files automatically.

$ mkdir certs newcerts private
$ touch index.txt
$ echo 1000 > serial

Each file and directory serves a specific purpose:

certs
directory containing certificates (*.crt.pem) and certificate signing requests (*.csr.pem)
newcerts
directory containing copies of generated certificates and named according to their serial number.
This directory will be managed by OpenSSL.
private
directory containing generated private RSA keys (*.key.pem)
index.txt
The database file mapping certificate subject lines and serial numbers.
OpenSSL will handle the organization of this file
serial
A file containing the next certificate serial number (in this case we start from 1000).
This number will be incremented after signing a new certificate.

Configuration

OpenSSL commands can be quite complex depending on the options given such as directory structure, key sizes, and locality information. If an option is unspecified, it will assume its default value specified in the OpenSSL configuration file. The default configuration file is located in /etc/ssl/openssl.cnf.

Below is a modified copy of the default configuration file with some additional extensions (v3_ca, v3_req, etc.) that allow us to set certificate properties for specific purposes. Copy the configuration below and save it to openssl.cnf in your CA base directory.

Note: Pay close attention to the values in the CA_default.dir, req.default_bits, and req_distinguished_name.*_default options. If you wish to set up a published certificate revocation list (recommended), please change the crlDistributionPoints configuration values in [v3_ca] and [client_cert]
#
# OpenSSL example configuration file.
# This is mostly being used for generation of certificate requests.
#

# This definition stops the following lines choking if HOME isn't
# defined.
HOME                        = .
RANDFILE                    = $ENV::HOME/.rnd

# Extra OBJECT IDENTIFIER info:
#oid_file                    = $ENV::HOME/.oid
oid_section                 = new_oids

# To use this configuration file with the "-extfile" option of the
# "openssl x509" utility, name here the section containing the
# X.509v3 extensions to use:
# extensions                =
# (Alternatively, use a configuration file that has only
# X.509v3 extensions in its main [= default] section.)

[ new_oids ]

# We can add new OIDs in here for use by 'ca', 'req' and 'ts'.
# Add a simple OID like this:
# testoid1=1.2.3.4
# Or use config file substitution like this:
# testoid2=${testoid1}.5.6

# Policies used by the TSA examples.
tsa_policy1 = 1.2.3.4.1
tsa_policy2 = 1.2.3.4.5.6
tsa_policy3 = 1.2.3.4.5.7

####################################################################
[ ca ]
default_ca        = CA_default               # The default ca section

####################################################################
[ CA_default ]

dir               = .                        # Where everything is kept
certs             = $dir/certs               # Where the issued certs are kept
crl_dir           = $dir/crl                 # Where the issued crl are kept
database          = $dir/index.txt           # database index file.
#unique_subject    = no                       # Set to 'no' to allow creation of
                                             # several ctificates with same subject.
new_certs_dir     = $dir/newcerts            # default place for new certs.

certificate       = $dir/ca.crt.pem          # The CA certificate
serial            = $dir/serial              # The current serial number
crlnumber         = $dir/crlnumber           # the current crl number
                                             # must be commented out to leave a V1 CRL
crl               = $dir/crl.pem             # The current CRL
private_key       = $dir/private/ca.key.pem  # The private key
RANDFILE          = $dir/private/.rand       # private random number file

x509_extensions   = usr_cert                 # The extentions to add to the cert

# Comment out the following two lines for the "traditional"
# (and highly broken) format.
name_opt         = ca_default                # Subject Name options
cert_opt         = ca_default                # Certificate field options

# Extension copying option: use with caution.
# copy_extensions = copy

# Extensions to add to a CRL. Note: Netscape communicator chokes on V2 CRLs
# so this is commented out by default to leave a V1 CRL.
# crlnumber must also be commented out to leave a V1 CRL.
crl_extensions            = crl_ext

default_days              = 3650             # how long to certify for
default_crl_days          = 30               # how long before next CRL
default_md                = default          # use public key default MD
preserve                  = no               # keep passed DN ordering

# A few difference way of specifying how similar the request should look
# For type CA, the listed attributes must be the same, and the optional
# and supplied fields are just that :-)
policy                    = policy_match

# For the CA policy
[ policy_match ]
countryName               = match
stateOrProvinceName       = match
organizationName          = match
organizationalUnitName    = optional
commonName                = supplied
emailAddress              = optional

# For the 'anything' policy
# At this point in time, you must list all acceptable 'object'
# types.
[ policy_anything ]
countryName               = optional
stateOrProvinceName       = optional
localityName              = optional
organizationName          = optional
organizationalUnitName    = optional
commonName                = supplied
emailAddress              = optional

####################################################################
[ req ]
default_bits              = 4096 #2048
default_keyfile           = generated.key.pem
distinguished_name        = req_distinguished_name
attributes                = req_attributes
x509_extensions           = v3_ca        # The extentions to add to the self signed cert

# Passwords for private keys if not present they will be prompted for
# input_password = secret
# output_password = secret

# This sets a mask for permitted string types. There are several options.
# default: PrintableString, T61String, BMPString.
# pkix         : PrintableString, BMPString (PKIX recommendation before 2004)
# utf8only: only UTF8Strings (PKIX recommendation after 2004).
# nombstr : PrintableString, T61String (no BMPStrings or UTF8Strings).
# MASK:XXXX a literal mask value.
# WARNING: ancient versions of Netscape crash on BMPStrings or UTF8Strings.
string_mask = utf8only

# req_extensions = v3_req # The extensions to add to a certificate request

[ req_distinguished_name ]
countryName                        = Country Name (2 letter code)
countryName_default                = US
countryName_min                    = 2
countryName_max                    = 2

stateOrProvinceName                = State or Province Name (full name)
stateOrProvinceName_default        = Texas

localityName                       = Locality Name (eg, city)
localityName_default               = Bryan

0.organizationName                 = Organization Name (eg, company)
0.organizationName_default         = Komputerwiz Web Design

# we can do this but it is not needed normally :-)
#1.organizationName                = Second Organization Name (eg, company)
#1.organizationName_default        = World Wide Web Pty Ltd

organizationalUnitName             = Organizational Unit Name (eg, section)
#organizationalUnitName_default    =

commonName                         = Common Name (e.g. server FQDN or YOUR name)
commonName_max                     = 64

emailAddress                       = Email Address
emailAddress_max                   = 64

# SET-ex3                          = SET extension number 3

[ req_attributes ]
challengePassword                  = A challenge password
challengePassword_min              = 4
challengePassword_max              = 20

unstructuredName                   = An optional company name


[ usr_cert ]

# These extensions are added when 'ca' signs a request.

# This goes against PKIX guidelines but some CAs do it and some software
# requires this to avoid interpreting an end user certificate as a CA.

basicConstraints=CA:FALSE

# Here are some examples of the usage of nsCertType. If it is omitted
# the certificate can be used for anything *except* object signing.

# This is OK for an SSL server.
# nsCertType                        = server

# For an object signing certificate this would be used.
# nsCertType = objsign

# For normal client use this is typical
# nsCertType = client, email

# and for everything including object signing:
# nsCertType = client, email, objsign

# This is typical in keyUsage for a client certificate.
# keyUsage = nonRepudiation, digitalSignature, keyEncipherment

# This will be displayed in Netscape's comment listbox.
nsComment                        = "OpenSSL Generated Certificate"

# PKIX recommendations harmless if included in all certificates.
subjectKeyIdentifier=hash
authorityKeyIdentifier=keyid,issuer

# This stuff is for subjectAltName and issuerAltname.
# Import the email address.
# subjectAltName=email:copy
# An alternative to produce certificates that aren't
# deprecated according to PKIX.
# subjectAltName=email:move

# Copy subject details
# issuerAltName=issuer:copy

# Distribution point for this CA's certificate revocation list
#crlDistributionPoints = URI:http://example.com/crl.pem

#nsCaRevocationUrl                = http://www.domain.dom/ca-crl.pem
#nsBaseUrl
#nsRevocationUrl
#nsRenewalUrl
#nsCaPolicyUrl
#nsSslServerName

# This is required for TSA certificates.
# extendedKeyUsage = critical,timeStamping


[ v3_req ]

# Extensions to add to a certificate request

basicConstraints = CA:FALSE
keyUsage = nonRepudiation, digitalSignature, keyEncipherment


[ v3_ca ]

# Extensions for a typical CA


# PKIX recommendation.

subjectKeyIdentifier=hash

authorityKeyIdentifier=keyid:always,issuer

# This is what PKIX recommends but some broken software chokes on critical
# extensions.
#basicConstraints = critical,CA:true
# So we do this instead.
basicConstraints = CA:true

# Key usage: this is typical for a CA certificate. However since it will
# prevent it being used as an test self-signed certificate it is best
# left out by default.
# keyUsage = cRLSign, keyCertSign

# Some might want this also
# nsCertType = sslCA, emailCA

# Include email address in subject alt name: another PKIX recommendation
# subjectAltName=email:copy
# Copy issuer details
# issuerAltName=issuer:copy

# DER hex encoding of an extension: beware experts only!
# obj=DER:02:03
# Where 'obj' is a standard or added object
# You can even override a supported extension:
# basicConstraints= critical, DER:30:03:01:01:FF

[ crl_ext ]

# CRL extensions.
# Only issuerAltName and authorityKeyIdentifier make any sense in a CRL.

# issuerAltName=issuer:copy
authorityKeyIdentifier=keyid:always

[ proxy_cert_ext ]
# These extensions should be added when creating a proxy certificate

# This goes against PKIX guidelines but some CAs do it and some software
# requires this to avoid interpreting an end user certificate as a CA.

basicConstraints=CA:FALSE

# Here are some examples of the usage of nsCertType. If it is omitted
# the certificate can be used for anything *except* object signing.

# This is OK for an SSL server.
# nsCertType                        = server

# For an object signing certificate this would be used.
# nsCertType = objsign

# For normal client use this is typical
# nsCertType = client, email

# and for everything including object signing:
# nsCertType = client, email, objsign

# This is typical in keyUsage for a client certificate.
# keyUsage = nonRepudiation, digitalSignature, keyEncipherment

# This will be displayed in Netscape's comment listbox.
nsComment                        = "OpenSSL Generated Certificate"

# PKIX recommendations harmless if included in all certificates.
subjectKeyIdentifier=hash
authorityKeyIdentifier=keyid,issuer

# This stuff is for subjectAltName and issuerAltname.
# Import the email address.
# subjectAltName=email:copy
# An alternative to produce certificates that aren't
# deprecated according to PKIX.
# subjectAltName=email:move

# Copy subject details
# issuerAltName=issuer:copy

# Distribution point for this CA's certificate revocation list
#crlDistributionPoints = URI:http://example.com/crl.pem

#nsCaRevocationUrl                = http://www.domain.dom/ca-crl.pem
#nsBaseUrl
#nsRevocationUrl
#nsRenewalUrl
#nsCaPolicyUrl
#nsSslServerName

# This really needs to be in place for it to be a proxy certificate.
proxyCertInfo=critical,language:id-ppl-anyLanguage,pathlen:3,policy:foo

####################################################################
[ tsa ]

default_tsa = tsa_config1        # the default TSA section

[ tsa_config1 ]

# These are used by the TSA reply generation only.
dir                     = ./demoCA                                    # TSA root directory
serial                  = $dir/tsaserial                              # The current serial number (mandatory)
crypto_device           = builtin                                     # OpenSSL engine to use for signing
signer_cert             = $dir/tsa.crt.pem                            # The TSA signing certificate
                                                                      # (optional)
certs                   = $dir/ca.crt.pem                             # Certificate chain to include in reply
                                                                      # (optional)
signer_key              = $dir/private/tsa.key.pem                    # The TSA private key (optional)

default_policy          = tsa_policy1                                 # Policy if request did not specify it
                                                                      # (optional)
other_policies          = tsa_policy2, tsa_policy3                    # acceptable policies (optional)
digests                 = md5, sha1                                   # Acceptable message digests (mandatory)
accuracy                = secs:1, millisecs:500, microsecs:100        # (optional)
clock_precision_digits  = 0                                           # number of digits after dot. (optional)
ordering                = yes                                         # Is ordering defined for timestamps?
                                                                      # (optional, default: no)
tsa_name                = yes                                         # Must the TSA name be included in the reply?
                                                                      # (optional, default: no)
ess_cert_id_chain       = no                                          # Must the ESS cert id chain be included?
                                                                      # (optional, default: no)


[ client_cert ]
authorityKeyIdentifier  = keyid,issuer
subjectKeyIdentifier    = hash
subjectAltName          = email:move
issuerAltName           = issuer:copy
basicConstraints        = CA:FALSE
nsCertType              = client, email, objsign
keyUsage                = nonRepudiation, digitalSignature, keyEncipherment

# Distribution point for this CA's certificate revocation list
#crlDistributionPoints = URI:http://example.com/crl.pem

From this point on, all commands must be executed from within this certificate authority base directory. Now that everything is set up, let's start generating certificates!