Ruby script to split certificate files (.pem)

split-pem

#!/usr/bin/env ruby

require "openssl"

BEGIN_CERT = "-----BEGIN CERTIFICATE-----"
END_CERT   = "-----END CERTIFICATE-----"

def debug(str)
  return unless ENV.key?("DEBUG")
  puts "[DEBUG] #{str}"
end

def fingerprint(cert)
  alg = "SHA256"
  Digest(alg.to_sym).hexdigest(cert.to_der).upcase.scan(/../).join(":")
end

abort "No filename given" if ARGV.empty?

input_file = ARGV.shift
input_lines = File.readlines(input_file).map(&:chomp)

certs = []
cert_lines = []

input_lines.each_with_index do |line, idx|
  debug line

  if line == BEGIN_CERT
    cert_lines = []
    cert_lines << line
  elsif line == END_CERT
    cert_lines << line
    certs << cert_lines
  else
    cert_lines << line
  end
end

raw_certs = certs.map { |cert_lines| cert_lines.join("\n") }
openssl_certs = raw_certs.map { |cert_data| OpenSSL::X509::Certificate.new(cert_data) }
txt_certs = openssl_certs.map { |openssl_cert| openssl_cert.to_text }

puts txt_certs.join("\n\n===\n\n")
puts "\n\nFingerprints\n\n"
openssl_certs.each { |cert| puts "https://crt.sh/?q=#{fingerprint(cert)}" }