OpenSSL::X509::CertificateError

Document-class: OpenSSL::X509::Certificate

Implementation of an X.509 certificate as specified in RFC 5280.
Provides access to a certificate's attributes and allows certificates
to be read from a string, but also supports the creation of new
certificates from scratch.

=== Reading a certificate from a file

Certificate is capable of handling DER-encoded certificates and
certificates encoded in OpenSSL's PEM format.

  raw = File.read "cert.cer" # DER- or PEM-encoded
  certificate = OpenSSL::X509::Certificate.new raw

=== Saving a certificate to a file

A certificate may be encoded in DER format

  cert = ...
  File.open("cert.cer", "wb") { |f| f.print cert.to_der }

or in PEM format

  cert = ...
  File.open("cert.pem", "wb") { |f| f.print cert.to_pem }

X.509 certificates are associated with a private/public key pair,
typically a RSA, DSA or ECC key (see also OpenSSL::PKey::RSA,
OpenSSL::PKey::DSA and OpenSSL::PKey::EC), the public key itself is
stored within the certificate and can be accessed in form of an
OpenSSL::PKey. Certificates are typically used to be able to associate
some form of identity with a key pair, for example web servers serving
pages over HTTPs use certificates to authenticate themselves to the user.

The public key infrastructure (PKI) model relies on trusted certificate
authorities ("root CAs") that issue these certificates, so that end
users need to base their trust just on a selected few authorities
that themselves again vouch for subordinate CAs issuing their
certificates to end users.

The OpenSSL::X509 module provides the tools to set up an independent
PKI, similar to scenarios where the 'openssl' command line tool is
used for issuing certificates in a private PKI.

=== Creating a root CA certificate and an end-entity certificate

First, we need to create a "self-signed" root certificate. To do so,
we need to generate a key first. Please note that the choice of "1"
as a serial number is considered a security flaw for real certificates.
Secure choices are integers in the two-digit byte range and ideally
not sequential but secure random numbers, steps omitted here to keep
the example concise.

  root_key = OpenSSL::PKey::RSA.new 2048 # the CA's public/private key
  root_ca = OpenSSL::X509::Certificate.new
  root_ca.version = 2 # cf. RFC 5280 - to make it a "v3" certificate
  root_ca.serial = 1
  root_ca.subject = OpenSSL::X509::Name.parse "/DC=org/DC=ruby-lang/CN=Ruby CA"
  root_ca.issuer = root_ca.subject # root CA's are "self-signed"
  root_ca.public_key = root_key.public_key
  root_ca.not_before = Time.now
  root_ca.not_after = root_ca.not_before + 2 * 365 * 24 * 60 * 60 # 2 years validity
  ef = OpenSSL::X509::ExtensionFactory.new
  ef.subject_certificate = root_ca
  ef.issuer_certificate = root_ca
  root_ca.add_extension(ef.create_extension("basicConstraints","CA:TRUE",true))
  root_ca.add_extension(ef.create_extension("keyUsage","keyCertSign, cRLSign", true))
  root_ca.add_extension(ef.create_extension("subjectKeyIdentifier","hash",false))
  root_ca.add_extension(ef.create_extension("authorityKeyIdentifier","keyid:always",false))
  root_ca.sign(root_key, OpenSSL::Digest::SHA256.new)

The next step is to create the end-entity certificate using the root CA
certificate.

  key = OpenSSL::PKey::RSA.new 2048
  cert = OpenSSL::X509::Certificate.new
  cert.version = 2
  cert.serial = 2
  cert.subject = OpenSSL::X509::Name.parse "/DC=org/DC=ruby-lang/CN=Ruby certificate"
  cert.issuer = root_ca.subject # root CA is the issuer
  cert.public_key = key.public_key
  cert.not_before = Time.now
  cert.not_after = cert.not_before + 1 * 365 * 24 * 60 * 60 # 1 years validity
  ef = OpenSSL::X509::ExtensionFactory.new
  ef.subject_certificate = cert
  ef.issuer_certificate = root_ca
  cert.add_extension(ef.create_extension("keyUsage","digitalSignature", true))
  cert.add_extension(ef.create_extension("subjectKeyIdentifier","hash",false))
  cert.sign(root_key, OpenSSL::Digest::SHA256.new)