inspect_pem.rb

#!/usr/bin/env ruby

require 'base64'
require 'openssl'
require 'pp'

if ARGV.size != 1
  puts "Usage: #{$0} <pem file>"
  exit 1
end

pem_path = ARGV[0]
der_path = "#{pem_path}.der"
cert_path = "#{der_path}.cert"

pem = File.readlines(pem_path)[1..-2].map(&:strip).join('')
der = nil

puts "Unpacking #{pem_path} to #{der_path} .."
File.open(der_path, 'w') do |f|
  der = Base64.decode64(pem)
  f.write der
end

puts "Decoding #{der_path} to #{cert_path} .."
File.open(cert_path, 'w') do |f|
  PP.pp OpenSSL::ASN1.decode(der), f
end