Add post-quantum cryptography (PQC) support to SSLConfig

lib/drb/drb.rb

@@ -463,6 +463,9 @@ def initialize(error)
     attr_reader :reason
   end
 
+  # Error raised when an error occurs on the bad configuration.
+  class DRbBadConfig < DRbError; end
+
   # Class wrapping a marshalled object whose type is unknown locally.
   #
   # If an object is returned by a method invoked over drb, but the

lib/drb/ssl.rb

@@ -25,19 +25,25 @@ class SSLConfig
       #
       # See DRb::DRbSSLSocket::SSLConfig.new for more details
       DEFAULT = {
-        :SSLCertificate       => nil,
-        :SSLPrivateKey        => nil,
-        :SSLClientCA          => nil,
-        :SSLCACertificatePath => nil,
-        :SSLCACertificateFile => nil,
-        :SSLTmpDhCallback     => nil,
-        :SSLVerifyMode        => ::OpenSSL::SSL::VERIFY_NONE,
-        :SSLVerifyDepth       => nil,
-        :SSLVerifyCallback    => nil,   # custom verification
-        :SSLCertificateStore  => nil,
+        :SSLCertificates              => nil,
+        :SSLCertificate               => nil,
+        :SSLPrivateKey                => nil,
+        :SSLPrivateKeyAlgorithms      => ["RSA"],
+        :SSLClientCA                  => nil,
+        :SSLCACertificatePath         => nil,
+        :SSLCACertificateFile         => nil,
+        :SSLSignatureAlgorithms       => nil,
+        :SSLClientSignatureAlgorithms => nil,
+        :SSLGroups                    => nil,
+        :SSLTmpDhCallback             => nil,
+        :SSLVerifyMode                => ::OpenSSL::SSL::VERIFY_NONE,
+        :SSLVerifyDepth               => nil,
+        :SSLVerifyCallback            => nil,   # custom verification
+        :SSLCertificateStore          => nil,
         # Must specify if you use auto generated certificate.
-        :SSLCertName          => nil,   # e.g. [["CN","fqdn.example.com"]]
-        :SSLCertComment       => "Generated by Ruby/OpenSSL"
+        # e.g. [["CN", "fqdn.example.com"]]
+        :SSLCertName                  => nil,
+        :SSLCertComment               => "Generated by Ruby/OpenSSL"
       }
 
       # Create a new DRb::DRbSSLSocket::SSLConfig instance
@@ -51,13 +57,29 @@ class SSLConfig
       #
       # From +config+ Hash:
       #
+      # :SSLCertificates ::
+      #   An Array of [certificate, private_key] pairs. Each element
+      #   is an Array of an OpenSSL::X509::Certificate and its
+      #   corresponding private key.  This option is prioritized over
+      #   :SSLCertificate and :SSLPrivateKey.  See
+      #   OpenSSL::SSL::SSLContext#add_certificate
+      #
       # :SSLCertificate ::
       #   An instance of OpenSSL::X509::Certificate.  If this is not provided,
       #   then a generic X509 is generated, with a correspond :SSLPrivateKey
       #
       # :SSLPrivateKey ::
-      #   A private key instance, like OpenSSL::PKey::RSA.  This key must be
-      #   the key that signed the :SSLCertificate
+      #   A private key instance, like OpenSSL::PKey::RSA for RSA
+      #   and OpenSSL::PKey::PKey for ML-DSA-44, ML-DSA-65,
+      #   ML-DSA-87.  This key must be the key that signed the
+      #   :SSLCertificate
+      #
+      # :SSLPrivateKeyAlgorithms ::
+      #   An Array of private key algorithms used to generate
+      #   certificates when :SSLCertificates, :SSLCertificate and
+      #   :SSLPrivateKey are not provided. Supported algorithms are
+      #   RSA, ML-DSA-44, ML-DSA-65, and ML-DSA-87.
+      #   Defaults to ["RSA"]
       #
       # :SSLClientCA ::
       #   An OpenSSL::X509::Certificate, or Array of certificates that will
@@ -70,6 +92,15 @@ class SSLConfig
       # :SSLCACertificateFile ::
       #   A path to a CA certificate file, in PEM format.
       #
+      # :SSLSignatureAlgorithms ::
+      #   Signature algorithms.  See OpenSSL::SSL::SSLContext#sigalgs=
+      #
+      # :SSLClientSignatureAlgorithms ::
+      #   Client signature algorithms.  See OpenSSL::SSL::SSLContext#client_sigalgs=
+      #
+      # :SSLGroups ::
+      #   Key exchange groups.  See OpenSSL::SSL::SSLContext#groups=
+      #
       # :SSLTmpDhCallback ::
       #   A DH callback. See OpenSSL::SSL::SSLContext.tmp_dh_callback
       #
@@ -133,10 +164,15 @@ class SSLConfig
       #   c.setup_certificate
       #
       def initialize(config)
-        @config  = config
-        @cert    = config[:SSLCertificate]
-        @pkey    = config[:SSLPrivateKey]
-        @ssl_ctx = nil
+        @config   = config
+        @certs    = nil
+        if config[:SSLCertificate] && config[:SSLPrivateKey]
+          @certs = [[config[:SSLCertificate], config[:SSLPrivateKey]]]
+        end
+        @certs    = config[:SSLCertificates] if config.key?(:SSLCertificates)
+        @pkey_algs = config[:SSLPrivateKeyAlgorithms] ||
+                     self[:SSLPrivateKeyAlgorithms]
+        @ssl_ctx  = nil
       end
 
       # A convenience method to access the values like a Hash
@@ -162,25 +198,121 @@ def accept(tcp)
         ssl
       end
 
-      # Ensures that :SSLCertificate and :SSLPrivateKey have been provided
-      # or that a new certificate is generated with the other parameters
-      # provided.
+      # Ensures that :SSLCertificates or :SSLCertificate and
+      # :SSLPrivateKey have been provided, or that new certificates
+      # are generated with the other parameters provided.
       def setup_certificate
-        if @cert && @pkey
+        if @certs
           return
         end
 
-        rsa = OpenSSL::PKey::RSA.new(2048)
+        @certs = @pkey_algs.map { |pkey_alg| setup_certificate_one(pkey_alg) }
+      end
+
+      # Establish the OpenSSL::SSL::SSLContext with the configuration
+      # parameters provided.
+      def setup_ssl_context
+        ctx = ::OpenSSL::SSL::SSLContext.new
+        @certs&.each do |cert, pkey|
+          ctx.add_certificate(cert, pkey)
+        end
+        ctx.min_version     = self[:SSLMinVersion]
+        ctx.max_version     = self[:SSLMaxVersion]
+        ctx.client_ca       = self[:SSLClientCA]
+        ctx.ca_path         = self[:SSLCACertificatePath]
+        ctx.ca_file         = self[:SSLCACertificateFile]
+
+        if self[:SSLSignatureAlgorithms]
+          # OpenSSL::SSL::SSLContext#sigalgs=, #client_sigalgs=, #groups= were
+          # added in openssl gem 4.0.0.
+          # https://github.com/ruby/openssl/blob/v4.0.0/History.md?plain=1#L25-L31
+          # OpenSSL::SSL::SSLContext#sigalgs= is supported in OpenSSL >= 1.0.2.
+          # https://github.com/ruby/openssl/blob/v4.0.0/ext/openssl/extconf.rb#L142-L143
+          unless ctx.respond_to?(:sigalgs=)
+            raise(DRbBadConfig,
+                  unsupported_message(
+                    ':SSLSignatureAlgorithms', '4.0.0', '1.0.2'
+                  ))
+          end
+          ctx.sigalgs = self[:SSLSignatureAlgorithms]
+        end
+
+        if self[:SSLClientSignatureAlgorithms]
+          # OpenSSL::SSL::SSLContext#client_sigalgs= is supported in
+          # OpenSSL >= 1.0.2.
+          # https://github.com/ruby/openssl/blob/v4.0.0/ext/openssl/extconf.rb#L144-L145
+          unless ctx.respond_to?(:client_sigalgs=)
+            raise(DRbBadConfig,
+                  unsupported_message(
+                    ':SSLClientSignatureAlgorithms', '4.0.0', '1.0.2'
+                  ))
+          end
+          ctx.client_sigalgs = self[:SSLClientSignatureAlgorithms]
+        end
+
+        if self[:SSLGroups]
+          # OpenSSL::SSL::SSLContext#groups is supported in all OpenSSL
+          # versions.
+          # https://github.com/ruby/openssl/blob/v4.0.0/ext/openssl/ossl_ssl.c#L3031
+          unless ctx.respond_to?(:groups=)
+            raise(DRbBadConfig,
+                  unsupported_message(
+                    ':SSLGroups', '4.0.0'
+                  ))
+          end
+          ctx.groups = self[:SSLGroups]
+        end
+
+        ctx.tmp_dh_callback = self[:SSLTmpDhCallback]
+        ctx.verify_mode     = self[:SSLVerifyMode]
+        ctx.verify_depth    = self[:SSLVerifyDepth]
+        ctx.verify_callback = self[:SSLVerifyCallback]
+        ctx.cert_store      = self[:SSLCertificateStore]
+        @ssl_ctx = ctx
+      end
+
+      private
 
+      def setup_certificate_one(pkey_alg)
         cert = OpenSSL::X509::Certificate.new
+
+        case pkey_alg
+        when "RSA"
+          pkey = OpenSSL::PKey::RSA.new(2048)
+          cert.public_key = pkey.public_key
+          digest = "SHA256"
+        when "ML-DSA-44", "ML-DSA-65", "ML-DSA-87"
+          # openssl gem >= 4.0.0 and OpenSSL >= 3.5.0 support ML-DSA.
+          # https://github.com/ruby/openssl/blob/v4.0.0/History.md#notable-changes
+          # https://openssl-library.org/post/2025-04-08-openssl-35-final-release/
+          begin
+            pkey = OpenSSL::PKey.generate_key(pkey_alg)
+          rescue OpenSSL::PKey::PKeyError
+            raise(DRbBadConfig,
+                  unsupported_message(
+                    "#{pkey_alg} algorithm", '4.0.0', '3.5.0'
+                  ))
+          end
+          # OpenSSL::PKey::PKey#public_to_der was added in openssl gem 2.2.0.
+          # https://github.com/ruby/openssl/blob/v2.2.0/History.md?plain=1#L72-L75
+          cert.public_key = OpenSSL::PKey.read(pkey.public_to_der)
+          # OpenSSL::X509::Certificate#sign doesn't accept explicit digest
+          # algorithm, in ML-DSA because ML-DSA has a built-in digest.
+          digest = nil
+        else
+          raise(DRbBadConfig,
+                "#{pkey_alg} algorithm not found. "\
+                "RSA, ML-DSA-44, ML-DSA-65, and ML-DSA-87 "\
+                "algorithms are supported")
+        end
+
         cert.version = 2 # This means v3
         cert.serial = 0
         name = OpenSSL::X509::Name.new(self[:SSLCertName])
         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)
         cert.extensions = [
@@ -192,29 +324,19 @@ def setup_certificate
         if comment = self[:SSLCertComment]
           cert.add_extension(ef.create_extension("nsComment", comment))
         end
-        cert.sign(rsa, "SHA256")
+        cert.sign(pkey, digest)
 
-        @cert = cert
-        @pkey = rsa
+        [cert, pkey]
       end
 
-      # Establish the OpenSSL::SSL::SSLContext with the configuration
-      # parameters provided.
-      def setup_ssl_context
-        ctx = ::OpenSSL::SSL::SSLContext.new
-        ctx.cert            = @cert
-        ctx.key             = @pkey
-        ctx.min_version     = self[:SSLMinVersion]
-        ctx.max_version     = self[:SSLMaxVersion]
-        ctx.client_ca       = self[:SSLClientCA]
-        ctx.ca_path         = self[:SSLCACertificatePath]
-        ctx.ca_file         = self[:SSLCACertificateFile]
-        ctx.tmp_dh_callback = self[:SSLTmpDhCallback]
-        ctx.verify_mode     = self[:SSLVerifyMode]
-        ctx.verify_depth    = self[:SSLVerifyDepth]
-        ctx.verify_callback = self[:SSLVerifyCallback]
-        ctx.cert_store      = self[:SSLCertificateStore]
-        @ssl_ctx = ctx
+      def unsupported_message(name, ruby_openssl_version,
+                                  openssl_version=nil)
+        message = "#{name} not supported. "\
+          "Install openssl gem >= #{ruby_openssl_version}"
+        if openssl_version
+          message += " building with OpenSSL >= #{openssl_version}"
+        end
+        message
       end
     end
 

test/drb/drbtest.rb

@@ -4,6 +4,7 @@
 require 'drb/drb'
 require 'drb/extservm'
 require 'timeout'
+require_relative 'drbtest_utils'
 
 module DRbTests
 
@@ -393,4 +394,90 @@ def test_07_break_18
 
 end
 
+# A PQC Utilities module inspired from ruby/rubygems omit_unless_support_pqc
+module DRbPQCUtilities
+  # PQC algorithms ML-KEM and ML-DSA require OpenSSL >= 3.5.
+  # https://openssl-library.org/post/2025-04-08-openssl-35-final-release/
+  def support_pqc_openssl?
+    OpenSSL::OPENSSL_VERSION_NUMBER >= 0x30500000
+  end
+
+  # Ruby OpenSSL >= 4.0 supports OpenSSL::SSL::SSLContext#groups,
+  # OpenSSL::SSL::SSLSocket#sigalg, #peer_sigalg used in PQC cases, fixing the
+  # following issue.
+  # https://github.com/ruby/openssl/blob/v4.0.0/History.md#notable-changes
+  # https://github.com/ruby/openssl/commit/9614b7f67a629cc8d31b6fe5be5040c68263ca8b
+  def support_pqc_ruby_openssl?
+    Gem::Version.new(OpenSSL::VERSION) >= Gem::Version.new('4.0')
+  end
+
+  # Probe an actual PQC handshake between a forced-PQC server and a
+  # default-configured client, mirroring what the integration tests exercise.
+  # Memoized so the probe runs at most once per process.
+  def support_pqc_handshake?
+    return @support_pqc_handshake unless @support_pqc_handshake.nil?
+
+    @support_pqc_handshake = probe_pqc_handshake
+  end
+
+  def probe_pqc_handshake
+    server = TCPServer.new('127.0.0.1', 0)
+    ctx = OpenSSL::SSL::SSLContext.new
+    ctx.add_certificate(
+      Fixtures.read_cert('mldsa65_server.crt'),
+      Fixtures.read_pkey('mldsa65_server.key'))
+    ctx.groups = 'X25519MLKEM768'
+    ssl_server = OpenSSL::SSL::SSLServer.new(server, ctx)
+
+    port = server.addr[1]
+    server_thread = Thread.new do
+      client = ssl_server.accept
+      client.close
+    rescue OpenSSL::OpenSSLError
+      nil
+    end
+
+    client_ctx = OpenSSL::SSL::SSLContext.new
+    client_ctx.verify_mode = OpenSSL::SSL::VERIFY_NONE
+    socket = TCPSocket.new('127.0.0.1', port)
+    ssl = OpenSSL::SSL::SSLSocket.new(socket, client_ctx)
+    ssl.connect
+    ssl.close
+    true
+  rescue OpenSSL::OpenSSLError, SystemCallError
+    false
+  ensure
+    server_thread&.join(5)
+    server_thread&.kill if server_thread&.alive?
+    ssl_server&.close
+    server&.close
+  end
+
+  def omit_unless_support_pqc
+    unless support_pqc_openssl?
+      yield if block_given?
+      omit 'PQC algorithms require OpenSSL >= 3.5'
+      return
+    end
+    unless support_pqc_ruby_openssl?
+      yield if block_given?
+      omit 'PQC test requires Ruby OpenSSL >= 4.0'
+      return
+    end
+    unless support_pqc_handshake?
+      yield if block_given?
+      omit 'PQC handshake is not available in this OpenSSL configuration'
+    end
+  end
+end
+
+module DRbPQC
+  include DRbBase
+  include DRbPQCUtilities
+
+  def test_01_hello
+    assert_equal('hello', @there.hello)
+  end
+end
+
 end