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Berk
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Creating Fullchain Self Signed SSL | Root & Intermediate CA

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.

Before Starting

  • Create a localCA folder in /etc/ssl
sudo mkdir -p /etc/ssl/localCA && \
cd /etc/ssl/localCA
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  • For non sudo commands, chown the directory.
sudo chown -R $USER:$USER /etc/ssl/localCA
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Create Root CA

  • Create a folder inside /etc/ssl/localCA named rootCA
mkdir -p /etc/ssl/localCA/rootCA && \
cd /etc/ssl/localCA/rootCA
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  • Create rootCA.key file
openssl genrsa -aes256 -out rootCA.key 4096
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  • Create a cnf file named rootCA.cnf
vim rootCA.cnf
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[ 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            = burakberkkeskin@gmail.com

[ 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
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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
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  • Create a newcerts directory
mkdir /etc/ssl/localCA/rootCA/newcerts
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  • Create a index.txt file
touch /etc/ssl/localCA/rootCA/index.txt && \
chmod 600 /etc/ssl/localCA/rootCA/index.txt
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  • Create a serial file
echo "1000" > /etc/ssl/localCA/rootCA/serial && \
chmod 600 /etc/ssl/localCA/rootCA/serial
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Create Intermediate CA

  • Create a intermediateCA folder
mkdir -p /etc/ssl/localCA/intermediateCA && \
cd /etc/ssl/localCA/intermediateCA 
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  • Create intermediateCA.key file
openssl genrsa -aes256 -out intermediateCA.key 4096
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  • Create a intermediateCA.cnf file
vim intermediateCA.cnf
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[ 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            = burakberkkeskin@gmail.com

[ 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
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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
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  • 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
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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
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  • Create a exampleApp.key file
openssl genpkey -algorithm RSA -out "${appname}.key"
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  • Create a exampleApp.cnf file
vim "${appname}.cnf"
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[ 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           = burakberkkeskin@gmail.com

[ v3_ext ]
subjectAltName = @alt_names

[ alt_names ]
DNS.1 = api.example.com
DNS.2 = app.example.com
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[!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 "${appname}.csr"
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  • Sign the exampleApp.csr with intermediateCA.key
openssl x509 -req -in "${appname}.csr" \
            -CA ../intermediateCA/intermediateCA.crt \
            -CAkey ../intermediateCA/intermediateCA.key \
            -CAcreateserial \
            -days 365 -extensions v3_ext \
            -extfile "${appname}.cnf" \
            -out "${appname}.crt"
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  • Create Fullchain Cert
cat ./${appname}.crt >> fullchain.crt && \
cat ../intermediateCA/intermediateCA.crt >> fullchain.crt && \
cat ../rootCA/rootCA.crt >> fullchain.crt
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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

For more blogs posts like this, you can check https://burakberk.dev !

Top comments (2)

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stegratech profile image
Steve

Just came across your post. It's exactly what I needed and works perfect. Thanks!

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berk profile image
Berk

I am glad to help friend. Have a nice day!