Add helper to retrieve CRL URIs from a certificate

lib/openssl/x509.rb

@@ -113,6 +113,39 @@ def authority_key_identifier
           key_id.nil? ? nil : key_id.value
         end
       end
+
+      module CrlDistributionPoints
+        include Helpers
+
+        # Get the distributionPoint fullName URI from the certificate's CRL
+        # distribution points extension, as described in RFC5280 Section
+        # 4.2.1.13
+        #
+        # Returns an array of strings or nil or raises ASN1::ASN1Error.
+        def crl_uris
+          ext = find_extension("crlDistributionPoints")
+          return nil if ext.nil?
+
+          cdp_asn1 = ASN1.decode(ext.value_der)
+          if cdp_asn1.tag_class != :UNIVERSAL || cdp_asn1.tag != ASN1::SEQUENCE
+            raise ASN1::ASN1Error "invalid extension"
+          end
+
+          crl_uris = cdp_asn1.map do |crl_distribution_point|
+            distribution_point = crl_distribution_point.value.find do |v|
+              v.tag_class == :CONTEXT_SPECIFIC && v.tag == 0
+            end
+            full_name = distribution_point&.value&.find do |v|
+              v.tag_class == :CONTEXT_SPECIFIC && v.tag == 0
+            end
+            full_name&.value&.find do |v|
+              v.tag_class == :CONTEXT_SPECIFIC && v.tag == 6 # uniformResourceIdentifier
+            end
+          end
+
+          crl_uris.map(&:value)
+        end
+      end
     end
 
     class Name
@@ -234,6 +267,7 @@ def cleanup
     class Certificate
       include Extension::SubjectKeyIdentifier
       include Extension::AuthorityKeyIdentifier
+      include Extension::CrlDistributionPoints
 
       def pretty_print(q)
         q.object_group(self) {

test/test_x509cert.rb

@@ -98,6 +98,21 @@ def test_extension
       assert_equal(ee1_exts[i].last, ext.critical?)
     }
 
+    ef = OpenSSL::X509::ExtensionFactory.new
+    ef.config = OpenSSL::Config.parse(<<~_cnf_)
+      [crlDistPts]
+      URI.1 = http://www.example.com/crl
+      URI.2 = ldap://ldap.example.com/cn=ca?certificateRevocationList;binary
+    _cnf_
+    cdp_cert = generate_cert(@ee1, @rsa1024, 3, ca_cert)
+    ef.subject_certificate = cdp_cert
+    cdp_cert.add_extension(ef.create_extension("crlDistributionPoints", "@crlDistPts"))
+    cdp_cert.sign(@rsa2048, "sha256")
+    assert_equal(
+      ["http://www.example.com/crl", "ldap://ldap.example.com/cn=ca?certificateRevocationList;binary"],
+      cdp_cert.crl_uris
+    )
+
     no_exts_cert = issue_cert(@ca, @rsa2048, 1, [], nil, nil)
     assert_equal nil, no_exts_cert.authority_key_identifier
     assert_equal nil, no_exts_cert.subject_key_identifier