Create a CA

Create the file and directory structure

mkdir -p /root/ca/{certs,crl,newcerts,private} /root/ca/intermediate/{certs,crl,csr,newcerts,private}
chmod 700 /root/ca/private /root/ca/intermediate/private
:>/root/ca/index.txt; :>/root/ca/intermediate/index.txt
echo 1000 > /root/ca/serial; echo 1000 > /root/ca/intermediate/serial
echo 1000 > /root/ca/intermediate/crlnumber

Create the root certificate

Paste the following contents into /root/ca/root_ca.cnf

# OpenSSL root CA configuration file.
# Copy to `/root/ca/root_ca.cnf`.

[ ca ]
default_ca = CA_default

[ CA_default ]
# 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/root_ca.key
certificate       = $dir/certs/root_ca.crt

# 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_days      = 375
preserve          = no
policy            = policy_strict

[ policy_strict ]
# The root CA should only sign intermediate certificates that match.
# See the POLICY FORMAT section of `man ca`.
countryName             = optional
stateOrProvinceName     = optional
organizationName        = optional
organizationalUnitName  = optional
commonName              = supplied
emailAddress            = optional

[ 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              = supplied
emailAddress            = optional

[ req ]
# Options for the `req` tool (`man req`).
default_bits        = 2048
distinguished_name  = req_distinguished_name
string_mask         = utf8only

# SHA-1 is deprecated, so use SHA-2 instead.
default_md          = sha256

# 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>.
commonName                      = Common Name
countryName                     = Country Name (2 letter code)
stateOrProvinceName             = State or Province Name
localityName                    = Locality Name
0.organizationName              = Organization Name
organizationalUnitName          = Organizational Unit Name
emailAddress                    = Email Address

# Optionally, specify some defaults.
countryName_default             =
stateOrProvinceName_default     =
localityName_default            =
0.organizationName_default      =
organizationalUnitName_default  =
emailAddress_default            =

[ v3_ca ]
# Extensions for a typical CA (`man x509v3_config`).
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer
basicConstraints = critical, CA:true
keyUsage = critical, cRLSign, keyCertSign

[ v3_intermediate_ca ]
# Extensions for a typical intermediate CA (`man x509v3_config`).
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer
basicConstraints = critical, CA:true, pathlen:0
keyUsage = critical, cRLSign, keyCertSign

[ usr_cert ]
# Extensions for client certificates (`man x509v3_config`).
basicConstraints = CA:FALSE
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer
keyUsage = critical, nonRepudiation, digitalSignature, keyEncipherment
extendedKeyUsage = clientAuth, emailProtection

[ server_cert ]
# Extensions for server certificates (`man x509v3_config`).
basicConstraints = CA:FALSE
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer:always
keyUsage = critical, nonRepudiation, digitalSignature, keyEncipherment
extendedKeyUsage = serverAuth

[ crl_ext ]
# Extension for CRLs (`man x509v3_config`).
authorityKeyIdentifier=keyid:always

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

Create the root CA key

openssl genpkey -aes256 -algorithm ED25519 -out private/root_ca.key
chmod 400 private/root_ca.key

Create the root CA certificate

openssl req -config root_ca.cnf -new -x509 -extensions v3_ca -days 14600 -key private/root_ca.key -out certs/root_ca.crt

Common Name []:Pwned Global Root CA
Country Name (2 letter code) []:
State or Province Name []:
Locality Name []:
Organization Name []:
Organizational Unit Name []:
Email Address []:

chmod 444 certs/root_ca.crt

Verify the root certificate

openssl x509 -text -noout -in certs/root_ca.crt

Create the intermediate certificate

Paste this into /root/ca/intermediate/intermediate_ca.cnf

# OpenSSL intermediate CA configuration file.
# Copy to `/root/ca/intermediate/intermediate_ca.cnf`

[ ca ]
default_ca = CA_default

[ CA_default ]
# Directory and file locations.
dir               = /root/ca/intermediate
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/intermediate_ca.key
certificate       = $dir/certs/intermediate_ca.crt

# For certificate revocation lists.
crlnumber         = $dir/crlnumber
crl               = $dir/crl/intermediate.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_days      = 375
preserve          = no
policy            = policy_loose

copy_extensions   = copy

[ policy_strict ]
# The root CA should only sign intermediate certificates that match.
# See the POLICY FORMAT section of `man ca`.
countryName             = optional
stateOrProvinceName     = optional
organizationName        = optional
organizationalUnitName  = optional
commonName              = supplied
emailAddress            = optional

[ 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              = supplied
emailAddress            = optional

[ req ]
# Options for the `req` tool (`man req`).
default_bits        = 2048
distinguished_name  = req_distinguished_name
string_mask         = utf8only

# SHA-1 is deprecated, so use SHA-2 instead.
default_md          = sha256

# 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>.
commonName                      = Common Name
countryName                     = Country Name (2 letter code)
stateOrProvinceName             = State or Province Name
localityName                    = Locality Name
0.organizationName              = Organization Name
organizationalUnitName          = Organizational Unit Name
emailAddress                    = Email Address

# Optionally, specify some defaults.
countryName_default             =
stateOrProvinceName_default     =
localityName_default            =
0.organizationName_default      =
organizationalUnitName_default  =
emailAddress_default            =

[ v3_ca ]
# Extensions for a typical CA (`man x509v3_config`).
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer
basicConstraints = critical, CA:true
keyUsage = critical, cRLSign, keyCertSign

[ v3_intermediate_ca ]
# Extensions for a typical intermediate CA (`man x509v3_config`).
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer
basicConstraints = critical, CA:true, pathlen:0
keyUsage = critical, cRLSign, keyCertSign

[ usr_cert ]
# Extensions for client certificates (`man x509v3_config`).
basicConstraints = CA:FALSE
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer
keyUsage = critical, nonRepudiation, digitalSignature, keyEncipherment
extendedKeyUsage = clientAuth, emailProtection

[ server_cert ]
# Extensions for server certificates (`man x509v3_config`).
basicConstraints = CA:FALSE
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer:always
keyUsage = critical, nonRepudiation, digitalSignature, keyEncipherment
extendedKeyUsage = serverAuth
#authorityInfoAccess = OCSP;URI:http://ocsp2.example.com

[ crl_ext ]
# Extension for CRLs (`man x509v3_config`).
authorityKeyIdentifier=keyid:always

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

Create the intermediate CA key

cd /root/ca/intermediate
openssl genpkey -aes256 -algorithm ED25519 -out private/intermediate_ca.key
chmod 400 private/intermediate_ca.key

Create the intermediate CA CSR

openssl req -config intermediate_ca.cnf -new -key private/intermediate_ca.key -out csr/intermediate_ca.csr

Common Name []:Pwned Global Intermediate CA
Country Name (2 letter code) []:
State or Province Name []:
Locality Name []:
Organization Name []:
Organizational Unit Name []:
Email Address []:

Sign the intermediary CA CSR to create the intermediate cert

cd /root/ca
openssl ca -config root_ca.cnf -extensions v3_intermediate_ca -days 3650 \
  -notext -in intermediate/csr/intermediate_ca.csr -out intermediate/certs/intermediate_ca.crt
chmod 444 intermediate/certs/intermediate_ca.crt

Verify the intermediate CA cert

openssl x509 -noout -text -in intermediate/certs/intermediate_ca.crt

Create chain file

cat intermediate/certs/intermediate_ca.crt certs/root_ca.crt > intermediate/certs/ca-chain.pem

Create server (leaf) certificate

Create a key for your certificate

cd /root/ca
openssl genpkey -algorithm ED25519 -out intermediate/private/www.example.com.key
chmod 400 intermediate/private/www.example.com.key

Create the certificate sign request

openssl req -config intermediate/intermediate_ca.cnf -key intermediate/private/www.example.com.key -new \
  -out intermediate/csr/www.example.com.csr -addext "subjectAltName = DNS:example.com,DNS:www.example.com"

Common Name []:www.example.com
Country Name (2 letter code) []:
State or Province Name []:
Locality Name []:
Organization Name []:
Organizational Unit Name []:
Email Address []:

Sign the certificate

openssl ca -config intermediate/intermediate_ca.cnf -extensions server_cert -days 365 \
  -notext -in intermediate/csr/www.example.com.csr -out intermediate/certs/www.example.com.crt

Verify the certificate

openssl x509 -text -noout -in intermediate/certs/www.example.com.crt

Create the fullchain cert

cat intermediate/certs/www.example.com.crt intermediate/certs/ca-chain.pem > intermediate/certs/www.example.com.pem