Creating Fullchain SSL Certificate With Bash • Burak Berk

Overview

After you follow this guide, you will became a local certificate authority that signs certs for web applications.

You will follow this steps:

Create a rootCA key and crt.
Create a intermediateCA (subCA) key and crt that is signed by rootCA.
Create a application key and crt that is signed by intermediateCA.
After all, you will have root, sub and app (fullchain) cert and key that is ready to be used in nginx or other stuf.

📚 If you want to automate this certificate creation process, you can check the crtforge post.

Before Starting

Create a localCA folder in /etc/ssl

sudo mkdir -p /etc/ssl/localCA && \
cd /etc/ssl/localCA

For non sudo commands, chown the directory.

sudo chown -R $USER:$USER /etc/ssl/localCA

Create Root CA

Create a folder inside /etc/ssl/localCA named rootCA

mkdir -p /etc/ssl/localCA/rootCA && \
cd /etc/ssl/localCA/rootCA

Create rootCA.key file

openssl genrsa -aes256 -out rootCA.key 4096

Create a cnf file named rootCA.cnf

vim rootCA.cnf

[ ca ]
# `man ca`
default_ca = CA_default

[ CA_default ]
# Directory and file locations.
dir               = /etc/ssl/localCA/rootCA
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/rootCA.key
certificate       = $dir/rootCA.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      = 3650
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             = 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.
# 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>.
countryName                     = Country Name 2 Letter
stateOrProvinceName             = State or Province Name
localityName                    = Locality Name
0.organizationName              = Organization Name
organizationalUnitName          = Organizational Unit Name
commonName                      = Common Name
emailAddress                    = Email Address

# Optionally, specify some defaults.
countryName_default             = TR
stateOrProvinceName_default     = Istanbul
localityName_default            = Istanbul
0.organizationName_default      = Safderun
organizationalUnitName_default  = Safderun ROOT CA
commonName_default              = Safderun ROOT CA
emailAddress_default            = [email protected]

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

[ usr_cert ]
# Extensions for client certificates (`man x509v3_config`).
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 (`man x509v3_config`).
basicConstraints = CA:FALSE
nsCertType = server
nsComment = "OpenSSL Generated Server Certificate"
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer:always
keyUsage = critical, 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

Caution ⚠️

Change the values lines in the rootCA.cnf file above:

countryName_default

stateOrProvinceName_default

localityName_default

0.organizationName_default

organizationalUnitName_default

commonName_default

emailAddress_default

Create the rootCA.crt file

openssl req -config rootCA.cnf \
            -key rootCA.key \
            -new -x509 -days 7305 -sha256 -extensions v3_ca \
            -out rootCA.crt

Create a newcerts directory

mkdir /etc/ssl/localCA/rootCA/newcerts

Create a index.txt file

touch /etc/ssl/localCA/rootCA/index.txt && \
chmod 600 /etc/ssl/localCA/rootCA/index.txt

Create a serial file

echo "1000" > /etc/ssl/localCA/rootCA/serial && \
chmod 600 /etc/ssl/localCA/rootCA/serial

Create Intermediate CA

Create a intermediateCA folder

mkdir -p /etc/ssl/localCA/intermediateCA && \
cd /etc/ssl/localCA/intermediateCA

Create intermediateCA.key file

openssl genrsa -aes256 -out intermediateCA.key 4096

Create a intermediateCA.cnf file

vim intermediateCA.cnf

[ ca ]
# `man 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.key.pem
certificate       = $dir/certs/intermediate.cert.pem

# 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

[ policy_strict ]
# The root CA should only sign intermediate certificates that match.
# See the POLICY FORMAT section of `man ca`.
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.
# 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>.
countryName                     = Country Name 2 Letter
stateOrProvinceName             = State or Province Name
localityName                    = Locality Name
0.organizationName              = Organization Name
organizationalUnitName          = Organizational Unit Name
commonName                      = Common Name
emailAddress                    = Email Address

# Optionally, specify some defaults.
countryName_default             = TR
stateOrProvinceName_default     = Istanbul
localityName_default            = Istanbul
0.organizationName_default      = Safderun
organizationalUnitName_default  = Safderun Intermediate CA
commonName_default              = Safderun Intermediate CA
emailAddress_default            = [email protected]

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

[ usr_cert ]
# Extensions for client certificates (`man x509v3_config`).
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 (`man x509v3_config`).
basicConstraints = CA:FALSE
nsCertType = server
nsComment = "OpenSSL Generated Server Certificate"
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer:always
keyUsage = critical, 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

Caution ⚠️

Change the values lines in the intermediateCA.cnf file above:

countryName_default

stateOrProvinceName_default

localityName_default

0.organizationName_default

organizationalUnitName_default

commonName_default

emailAddress_default

Create intermediateCA.csr file

openssl req -config intermediateCA.cnf \
            -new -sha256 \
            -keyout intermediateCA.key \
            -out intermediateCA.csr

Sign the intermediateCA.csr with rootCA.key file

openssl ca -config ../rootCA/rootCA.cnf \
            -extensions v3_intermediate_ca \
            -days 3650 -notext -md sha256 \
            -in intermediateCA.csr \
            -out intermediateCA.crt

Creating a SSL cert for your web app with domain

Create a directory named your application

export appname=exampleApp && \
mkdir -p /etc/ssl/localCA/$appname && \
cd /etc/ssl/localCA/$appname

Create a exampleApp.key file

openssl genpkey -algorithm RSA -out "${appname}.key"

Create a exampleApp.cnf file

vim "${appname}.cnf"

[ req ]
default_bits       = 2048
prompt             = no
default_md         = sha256
distinguished_name = dn

[ dn ]
countryName            = TR
stateOrProvinceName    = Istanbul
localityName           = Istanbul
organizationName       = Safderun
organizationalUnitName = Safderun Webapp
commonName             = example.com
emailAddress           = [email protected]

[ v3_ext ]
subjectAltName = @alt_names

[ alt_names ]
DNS.1 = api.example.com
DNS.2 = app.example.com

[!caution]
Change the values lines in the exampleApp.cnf file above:

countryName_default

stateOrProvinceName_default

localityName_default

0.organizationName_default

organizationalUnitName_default

commonName_default

emailAddress_default

DNS.1

Create a exampleApp.csr file

openssl req -new -key "${appname}.key" \
                 -config "${appname}.cnf" \
                 -out "${appname}.csr"

Sign the exampleApp.csr with intermediateCA.key

openssl x509 -req -in "${appname}.csr" \
            -CA ../intermediateCA/intermediateCA.crt \
            -CAkey ../intermediateCA/intermediateCA.key \
            -CAcreateserial \
            -days 365 -extensions v3_ext \
            -extfile "${appname}.cnf" \
            -out "${appname}.crt"

Create Fullchain Cert

cat ./${appname}.crt >> fullchain.crt && \
cat ../intermediateCA/intermediateCA.crt >> fullchain.crt && \
cat ../rootCA/rootCA.crt >> fullchain.crt

The Final

You have 3 folder. rootCA, intermediateCA and application directory. In the application directory, you have 5 files.

exampleApp.cnf: cert conf file
exampleApp.crt: public cert file
exampleApp.csr: cert signing request file
exampleApp.key: private key
fullchain.crt: Contains rootCA, intermediateCA and app cert which is ready to use.

You can use the fullchain cert and key file in a nginx server.

You can keep creating new certs for new web applications. All you need to do is repeating this step