cert_rsa_client.info

Here’s an explanation of the cert_rsa_client.sh script, which is designed for creating and managing RSA client certificates. This script automates directory setup, database serial number renewal, RSA key generation, CSR creation, certificate issuance, verification, and preparation of certificate chain bundles.

Here’s a detailed explanation:

Script Metadata link

• Filename: cert_rsa_client.sh
• Author: GJS (homelab-alpha)
• Date: June 9, 2024
• Version: 1.0.1
• Description: Automates the process of creating and managing RSA client certificates, including key generation, CSR creation, certificate issuance, verification, and preparation of certificate chain bundles.
• RAW Script: cert_rsa_client.sh

Detailed Explanation link

Functions link

1. print_cyan: This function prints text in cyan color to enhance readability in the terminal.

   print_cyan() {
     echo -e "\e[36m$1\e[0m" # \e[36m sets text color to cyan, \e[0m resets it
   }
   

   
   

2. generate_random_hex: This function generates a random hexadecimal value, which is useful for serial numbers and CRL numbers.

   generate_random_hex() {
     openssl rand -hex 16
   }
   

   
   

3. print_section_header: This function prints section headers in cyan to clearly separate different parts of the script.

   print_section_header() {
     echo ""
     echo ""
     echo -e "$(print_cyan "=== $1 === ")"
   }
   

Main Script Execution link

Prompt for Certificate Information link

The script prompts the user for the certificate name and FQDN.

read -r -p "$(print_cyan "Enter the name of the new certificate: ")" file_name
read -r -p "$(print_cyan "Enter the FQDN name of the new certificate: ")" fqdn

Define Directory Paths link

It defines the directory paths for storing SSL files and certificates.

print_section_header "Define directory paths"
ssl_dir="$HOME/ssl"
certificates_dir="$ssl_dir/certificates"
intermediate_dir="$ssl_dir/intermediate"

Renew Database Serial Numbers link

The script renews database serial numbers by generating random hex values and writing them to the respective serial files for the root, intermediate, and TSA directories.

print_section_header "Renew db serial numbers"
for dir in "$ssl_dir/root/db" "$intermediate_dir/db" "$ssl_dir/tsa/db"; do
  generate_random_hex >"$dir/serial"
done
generate_random_hex >"$ssl_dir/root/db/crlnumber"
generate_random_hex >"$intermediate_dir/db/crlnumber"

Generate RSA Key link

It generates an RSA key and saves it in the private directory for the client certificate.

print_section_header "Generate RSA key"
openssl genrsa -out "$certificates_dir/private/${file_name}.pem"

Generate Certificate Signing Request (CSR) link

The script creates a CSR for the client certificate using the generated RSA key and a configuration file.

print_section_header "Generate Certificate Signing Request (CSR)"
openssl req -new -sha256 -config "$certificates_dir/cert.cnf" -key "$certificates_dir/private/${file_name}.pem" -out "$certificates_dir/csr/${file_name}.pem"

Create an Extfile with All the Alternative Names and Settings link

It creates an extfile with parameters for the client certificate, such as subject alternative names (SANs), key usage, and extended key usage.

print_section_header "Create an extfile with all the alternative names"
{
  echo "subjectAltName = DNS:${fqdn}, DNS:www.${fqdn}"
  echo "basicConstraints = critical, CA:FALSE"
  echo "keyUsage = critical, digitalSignature"
  echo "extendedKeyUsage = clientAuth, emailProtection"
  echo "nsCertType = client, email"
  echo "nsComment = OpenSSL Generated Client Certificate"
} >>"$certificates_dir/extfile/${file_name}.cnf"

Generate Certificate link

The script issues the client certificate based on the CSR and extfile, valid for a specified period.

print_section_header "Generate Certificate"
openssl ca -config "$certificates_dir/cert.cnf" -notext -batch -in "$certificates_dir/csr/${file_name}.pem" -out "$certificates_dir/certs/${file_name}.pem" -extfile "$certificates_dir/extfile/${file_name}.cnf"

Create Certificate Chain Bundle link

It creates a certificate chain bundle by concatenating the client certificate and the intermediate CA chain bundle.

print_section_header "Create Certificate Chain Bundle"
cat "$certificates_dir/certs/${file_name}.pem" "$intermediate_dir/certs/ca_chain_bundle.pem" >"$certificates_dir/certs/${file_name}_chain_bundle.pem"

Verification Steps link

The script performs several verification steps to ensure the integrity and correctness of the certificates and keys.

1. Verify Certificate against the Certificate Chain Bundle

   print_section_header "Verify ${file_name} Certificate against the ${file_name} Certificate chain Bundle"
   openssl verify -CAfile "$certificates_dir/certs/${file_name}_chain_bundle.pem" "$certificates_dir/certs/${file_name}.pem"
   

   
   

2. Verify Certificate against the Intermediate Certificate Authority Chain Bundle

   print_section_header "Verify ${file_name} Certificate against the Intermediate Certificate Authority Chain Bundle"
   openssl verify -CAfile "$intermediate_dir/certs/ca_chain_bundle.pem" "$certificates_dir/certs/${file_name}.pem"
   

   
   

3. Verify Certificate Chain Bundle against the Intermediate Certificate Authority Chain Bundle

   print_section_header "Verify ${file_name} Certificate Chain Bundle against the Intermediate Certificate Authority Chain Bundle"
   openssl verify -CAfile "$intermediate_dir/certs/ca_chain_bundle.pem" "$certificates_dir/certs/${file_name}_chain_bundle.pem"
   

Check Generated Files link

The script includes steps to check the private key, CSR, client certificate, and the chain bundle to verify their contents.

1. Check Private Key

   print_section_header "Check Private Key"
   openssl rsa -in "$certificates_dir/private/${file_name}.pem" -text -noout
   

   
   

2. Check CSR

   print_section_header "Check Certificate Signing Request (CSR)"
   openssl req -text -noout -verify -in "$certificates_dir/csr/${file_name}.pem"
   

   
   

3. Check Certificate

   print_section_header "Check Certificate"
   openssl x509 -in "$certificates_dir/certs/${file_name}.pem" -text -noout
   

   
   

4. Check Certificate Chain Bundle

   print_section_header "Check Certificate Chain Bundle"
   openssl x509 -in "$certificates_dir/certs/${file_name}_chain_bundle.pem" -text -noout
   

Convert Certificate to Different Formats link

The script converts the certificate from PEM to CRT and KEY formats for compatibility with various applications.

print_section_header "Convert Certificate from ${fqdn}.pem to"
cat "$certificates_dir/certs/${file_name}.pem" >"$certificates_dir/certs/${file_name}.crt"
cat "$certificates_dir/certs/${file_name}_chain_bundle.pem" >"$certificates_dir/certs/${file_name}_chain_bundle.crt"
cat "$certificates_dir/private/${file_name}.pem" >"$certificates_dir/private/${file_name}.key"
chmod 600 "$certificates_dir/private/${file_name}.key"
echo -e "$(print_cyan "--> ")""${fqdn}.crt"
echo -e "$(print_cyan "--> ")""${fqdn}_chain_bundle.crt"
echo -e "$(print_cyan "--> ")""${fqdn}.key"

Conclusion link

This script ensures that every step in generating and managing an RSA client certificate is performed correctly and securely, from key generation to certificate verification and format conversion.