create a self-signed certificate using ruby-openssl

self_signed_cert.rb

require 'rubygems'
require 'openssl'

def create_self_signed_cert(bits=2048)
  key = OpenSSL::PKey::RSA.new(2048) 

  public_key = key.public_key

  subject = "/C=BE/O=Fable/OU=Fable/CN=Fable"

  cert = OpenSSL::X509::Certificate.new
  cert.subject = cert.issuer = OpenSSL::X509::Name.parse(subject)
  cert.not_before = Time.now
  cert.not_after = Time.now + 365 * 24 * 60 * 60
  cert.public_key = public_key
  cert.serial = 0x0
  cert.version = 2

  ef = OpenSSL::X509::ExtensionFactory.new
  ef.subject_certificate = cert
  ef.issuer_certificate = cert
  cert.extensions = [
    ef.create_extension("basicConstraints","CA:TRUE", true),
    ef.create_extension("subjectKeyIdentifier", "hash"),
    # ef.create_extension("keyUsage", "cRLSign,keyCertSign", true),
  ]
  cert.add_extension ef.create_extension("authorityKeyIdentifier",
  "keyid:always,issuer:always")

  cert.sign key, OpenSSL::Digest::SHA256.new

  return cert, key
end

WEBRick Cert generation

# From https://github.com/ruby/ruby/blob/trunk/lib/webrick/ssl.rb
require 'openssl'

def create_self_signed_cert(bits, cn, comment)
  rsa = OpenSSL::PKey::RSA.new(bits){|p, n|
    case p
    when 0; $stderr.putc "."  # BN_generate_prime
    when 1; $stderr.putc "+"  # BN_generate_prime
    when 2; $stderr.putc "*"  # searching good prime,
      # n = #of try,
      # but also data from BN_generate_prime
    when 3; $stderr.putc "\n" # found good prime, n==0 - p, n==1 - q,
      # but also data from BN_generate_prime
    else;   $stderr.putc "*"  # BN_generate_prime
    end
  }
  cert = OpenSSL::X509::Certificate.new
  cert.version = 2
  cert.serial = 1
  name = OpenSSL::X509::Name.new(cn)
  cert.subject = name
  cert.issuer = name
  cert.not_before = Time.now
  cert.not_after = Time.now + (365*24*60*60)
  cert.public_key = rsa.public_key

  ef = OpenSSL::X509::ExtensionFactory.new(nil,cert)
  ef.issuer_certificate = cert
  cert.extensions = [
    ef.create_extension("basicConstraints","CA:FALSE"),
    ef.create_extension("keyUsage", "keyEncipherment"),
    ef.create_extension("subjectKeyIdentifier", "hash"),
    ef.create_extension("extendedKeyUsage", "serverAuth"),
    ef.create_extension("nsComment", comment),
  ]
  aki = ef.create_extension("authorityKeyIdentifier",
  "keyid:always,issuer:always")
  cert.add_extension(aki)
  cert.sign(rsa, OpenSSL::Digest::SHA1.new)

  return [ cert, rsa ]
end