`require 'openssl'

name = OpenSSL::X509::Name.parse("CN=example.com/C=EE")
cert = OpenSSL::X509::Certificate.new
cert.version     = 2
cert.serial      = 0
cert.not_before  = Time.now
cert.not_after   = cert.not_before + 1 * 365 * 24 * 60 * 60 # 1 year validity
key = OpenSSL::PKey::RSA.new(2048)
cert.public_key  = key.public_key
cert.subject     = name
cert.issuer = name
cert.sign key, OpenSSL::Digest::SHA1.new
cert_path = "C:/temp/cert.der"
open cert_path, "w" do |io| io.write cert.to_der end

begin
raw = File.read cert_path  # DER- or PEM-encoded
certificate = OpenSSL::X509::Certificate.new raw
puts certificate.inspect
rescue  => exception
puts exception.backtrace
puts exception.inspect
end