OpenSSL::OCSP

OpenSSL::OCSP implements Online Certificate Status Protocol requests and responses.

Creating and sending an OCSP request requires a subject certificate that contains an OCSP URL in an authorityInfoAccess extension and the issuer certificate for the subject certificate. First, load the issuer and subject certificates:

subject = OpenSSL::X509::Certificate.new subject_pem
issuer  = OpenSSL::X509::Certificate.new issuer_pem

To create the request we need to create a certificate ID for the subject certificate so the CA knows which certificate we are asking about:

digest = OpenSSL::Digest::SHA1.new
certificate_id =
  OpenSSL::OCSP::CertificateId.new subject, issuer, digest

Then create a request and add the certificate ID to it:

request = OpenSSL::OCSP::Request.new
request.add_certid certificate_id

Adding a nonce to the request protects against replay attacks but not all CA process the nonce.

request.add_nonce

To submit the request to the CA for verification we need to extract the OCSP URI from the subject certificate:

authority_info_access = subject.extensions.find do |extension|
  extension.oid == 'authorityInfoAccess'
end

descriptions = authority_info_access.value.split "\n"
ocsp = descriptions.find do |description|
  description.start_with? 'OCSP'
end

require 'uri'

ocsp_uri = URI ocsp[/URI:(.*)/, 1]

To submit the request we’ll POST the request to the OCSP URI (per RFC 2560). Note that we only handle HTTP requests and don’t handle any redirects in this example, so this is insufficient for serious use.

require 'net/http'

http_response =
  Net::HTTP.start ocsp_uri.hostname, ocsp.port do |http|
    http.post ocsp_uri.path, request.to_der,
              'content-type' => 'application/ocsp-request'
end

response = OpenSSL::OCSP::Response.new http_response.body
response_basic = response.basic

First we check if the response has a valid signature. Without a valid signature we cannot trust it. If you get a failure here you may be missing a system certificate store or may be missing the intermediate certificates.

store = OpenSSL::X509::Store.new
store.set_default_paths

unless response.verify [], store then
  raise 'response is not signed by a trusted certificate'
end

The response contains the status information (success/fail). We can display the status as a string:

puts response.status_string #=> successful

Next we need to know the response details to determine if the response matches our request. First we check the nonce. Again, not all CAs support a nonce. See Request#check_nonce for the meanings of the return values.

p request.check_nonce basic_response #=> value from -1 to 3

Then extract the status information from the basic response. (You can check multiple certificates in a request, but for this example we only submitted one.)

response_certificate_id, status, reason, revocation_time,
  this_update, next_update, extensions = basic_response.status

Then check the various fields.

unless response_certificate_id == certificate_id then
  raise 'certificate id mismatch'
end

now = Time.now

if this_update > now then
  raise 'update date is in the future'
end

if now > next_update then
  raise 'next update time has passed'
end