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.new('SHA1')
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:

ocsp_uris = subject.ocsp_uris

require 'uri'

ocsp_uri = URI ocsp_uris[0]

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_uri.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_basic.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 for the certificate from the basic response.

single_response = basic_response.find_response(certificate_id)

unless single_response
  raise 'basic_response does not have the status for the certificate'
end

Then check the validity. A status issued in the future must be rejected.

unless single_response.check_validity
  raise 'this_update is in the future or next_update time has passed'
end

case single_response.cert_status
when OpenSSL::OCSP::V_CERTSTATUS_GOOD
  puts 'certificate is still valid'
when OpenSSL::OCSP::V_CERTSTATUS_REVOKED
  puts "certificate has been revoked at #{single_response.revocation_time}"
when OpenSSL::OCSP::V_CERTSTATUS_UNKNOWN
  puts 'responder doesn't know about the certificate'
end