Hi,

steps to create a CA. Create the CA structure in filesystem

mkdir -p CA
mkdir -p CA/crl CA/certs CA/newcerts CA/private CA/conf

Create the openssl config file /root/CA/conf/openssl.cnf

#
# openssl.cnf root CA config 
#
# /root/CA/conf/openssl.cnf
#
[ ca ]
default_ca = myCARoot

[ myCARoot ]
# Directory and file locations.
dir               = /root/CA
certs             = $dir/certs
crl_dir           = $dir/crl
new_certs_dir     = $dir/newcerts
database          = $dir/index.txt
serial            = $dir/serial
RANDFILE          = $dir/private/.rand

# The root key and root certificate.
private_key       = $dir/private/ca.key
certificate       = $dir/certs/ca.cer

# For certificate revocation lists.
crlnumber         = $dir/crlnumber
crl               = $dir/crl/crl.pem
crl_extensions    = crl_ext
default_crl_days  = 90

# Use at least sha256
default_md        = sha256

name_opt          = ca_default
cert_opt          = ca_default
default_days      = 3650
preserve          = no
policy            = policy_strict

[ policy_strict ]
# The root CA should only sign intermediate certificates that match.
countryName             = match
stateOrProvinceName     = match
organizationName        = match
organizationalUnitName  = optional
commonName              = supplied
emailAddress            = optional

[ policy_loose ]
# Allow the intermediate CA to sign a more diverse range of certificates.
countryName             = optional
stateOrProvinceName     = optional
localityName            = optional
organizationName        = optional
organizationalUnitName  = optional
commonName              = supplied
emailAddress            = optional

[ req ]
default_bits        = 2048
distinguished_name  = req_distinguished_name
string_mask         = utf8only

# Use at least sha256
default_md          = sha256

# Extension for -x509 option
x509_extensions     = v3_root_ca

[ req_distinguished_name ]
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
emailAddress                    = Email Address

# Defaults
countryName_default             = DE
stateOrProvinceName_default     = Germany
localityName_default            = Nuremberg
0.organizationName_default      = my Company
organizationalUnitName_default  = my Department
emailAddress_default            = me@mycompany.org

[ v3_root_ca ]
# Extensions for the CA
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer
basicConstraints = critical, CA:true
#keyUsage = critical, digitalSignature, cRLSign, keyCertSign
keyUsage = critical, cRLSign, keyCertSign
crlDistributionPoints=URI:http://yourDomain.org/crl/intermediateca-ca-crl.pem

[ v3_intermediate_ca ]
# Extensions for the intermediate CA
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer
basicConstraints = critical, CA:true, pathlen:0
#keyUsage = critical, digitalSignature, cRLSign, keyCertSign
keyUsage = critical, cRLSign, keyCertSign

[ client_cert ]
# Extensions for client certificates
basicConstraints = CA:FALSE
nsCertType = client, email
nsComment = "OpenSSL Generated Client Certificate"
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer
keyUsage = critical, nonRepudiation, digitalSignature, keyEncipherment
extendedKeyUsage = clientAuth, emailProtection

[ server_cert ]
# Extensions for server certificates
basicConstraints = CA:FALSE
nsCertType = server
nsComment = "OpenSSL Generated Server Certificate"
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer:always
keyUsage = critical, digitalSignature, keyEncipherment
extendedKeyUsage = serverAuth,clientAuth

[ crl_ext ]
# Extension for CRL
authorityKeyIdentifier=keyid:always

[ ocsp ]
# Extension for OCSP signing certificates
basicConstraints = CA:FALSE
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer
keyUsage = critical, digitalSignature
extendedKeyUsage = critical, OCSPSigning

create index und serial file

cd CA
touch index.txt
echo 1000 > crlnumber
echo 1000 > serial

If specified, openssl using the config defined at environment variable OPENSSL_CONF. Otherwise you have to set command line option -config for each command line call

export OPENSSL_CONF=/root/CA/conf/openssl.cnf
openssl genrsa -aes256 -out private/ca.key -passout pass:YourSecurePassword 4096
chmod 400 private/ca.key

Show key details

openssl rsa -in private/ca.key -text

Create the selfsigned certificate.

openssl req -key private/ca.key -new -x509 -days 3650 -sha256 -extensions v3_root_ca -out certs/ca.cer -subj "/C=DE/ST=Frankonia/L=Nuremberg/O=my Company/OU=my Department/CN=My root CA 2017" -passin pass:YourSecurePassword

View details of your new CA Root certificate

openssl x509 -in certs/ca.cer -text

That’s it 🙂

Next article is to create a intermediate CA

Michael