Add post-quantum cryptography (PQC) support to SSLConfig by junaruga · Pull Request #53 · ruby/drb

junaruga · 2026-07-29T10:35:51Z

This PR is related to #52.

Proof of concept

I prepared proof-of-concept scripts for this PR.

The document (drb/README.md) is here. A list of the sections in the drb/README.md is below. The sections without "(development)" test with the current master branch. These work. The sections with "(development)" test with this PR.

$ grep ^## drb/README.md
## druby (non-SSL)
## drbssl (SSL) auto-generated RSA cert
## drbssl (SSL) pre-generated RSA cert
## drbssl (SSL) pre-generated ML-DSA-65 cert
## drbssl (SSL) pre-generated RSA cert with client cert
## drbssl (SSL) pre-generated ML-DSA-65 cert with client cert
## drbssl (SSL) auto-generated ML-DSA-65 cert (development)
## drbssl (SSL) auto-generated ML-DSA-65/RSA multi cert (development)
## drbssl (SSL) pre-generated ML-DSA-65/RSA multi cert (development)
## drbssl (SSL) pre-generated ML-DSA-65/RSA multi cert with client cert (development)

The script is here. The CI result is here.

Commit message

DRb::DRbSSLSocket::SSLConfig already works
with pre-generated ML-DSA cert/key by
:SSLCertificate and :SSLPrivateKey config options.

This commit adds the following features in PQC use cases to #setup_certificate and #setup_ssl_context.

Add :SSLCertificates config option accepting an Array of [certificate, private_key] pairs for dual/multiple certificate support via OpenSSL::SSL::SSLContext#add_certificate changing from OpenSSL::SSL::SSLContext#cert and #key. Because an SSL server that accepts clients with either ML-DSA-NN or RSA certificates is useful in the use case of PQC migration from RSA (non-PQC) to ML-DSA (PQC). :SSLCertificate and :SSLPrivateKey are available for backward compatibility. But use OpenSSL::SSL::SSLContext#add_certificate internally. This is a behavior change.
Add :SSLPrivateKeyAlgorithms option accepting an Array of key algorithms (RSA, ML-DSA-44, ML-DSA-65, ML-DSA-87) for multi-certificate generation, defaulting to ["RSA"] for backward compatibility.
Add :SSLGroups option to control key exchange group such as ML-KEM in PQC.
Add :SSLSignatureAlgorithms, :SSLClientSignatureAlgorithms to control signature algorithms such as ML-DSA-NN in PQC, and RSA in non-PQC.
Add tool/create_certs.sh to generate test/drb/fixtures/*.{crt,key} to test with pre-generated certs/keys and add DRbTests::Fixtures module to read the certs/keys.
Add test/drb/test_ssl.rb to test lib/drb/ssl.rb as an unit test level. This approach aligns with test/drb/test_acl.rb to test lib/drb/acl.rb as an unit test level.
Add TestDRbSSLPQC, TestDRbSSLPQCMultiCertMLDSA65, TestDRbSSLPQCMultiCertRSA in test/drb/test_drbssl.rb. TestDRbSSLPQC is to test single PQC ML-KEM/ML-DSA server via test/drb/ut_drb_drbssl_pqc.rb. The testing class is inspired by TestDRbSSLCore. TestDRbSSLPQCMultiCertMLDSA65 and TestDRbSSLPQCMultiCertRSA are to test ML-DSA-65 (PQC) and RSA (non-PQC) dual (multiple) certificate server with client certificate via test/drb/ut_drb_drbssl_pqc_multi_cert.rb. The test is designed for a high-security use case with :SSLVerifyMode OpenSSL::SSL::VERIFY_PEER | OpenSSL::SSL::VERIFY_FAIL_IF_NO_PEER_CERT.

Assisted-by: Claude:claude-opus-4-6[1m]

Notes

CI cases supporting PQC

PQC (ML-KEM/ML-DSA) works in OpenSSL >= 3.5. OpenSSL 3.5 added the feature. And works in Ruby OpenSSL >= 4.0. Ruby OpenSSL 4.0.0 added some functions in PQC use cases, and fixed a bug.

The .github/workflows/test.yml uses runner ubuntu-latest, macos-latest, windows-latest.

According to https://github.com/actions/runner-images, ubuntu-latest is ubuntu-24.04, macos-latest is macOS-26-arm64, windows-latest is windows-2025-vs2026.

The ubuntu-24.04 uses OpenSSL 3.0.13 which doesn't support PQC. The windows-2025-vs2026 uses OpenSSL 3.6.3 which supports PQC. The macos-26 uses OpenSSL 3.6.2 which supports PQC. The new PQC tests should be executed on the macos-latest and windows-latest CI cases.

test/drb/test_ssl.rb testing lib/drb/ssl.rb as an unit test level

I checked all the existing test/drb/test_*.rb files.

test/drb/test_acl.rb tests drb/acl.rb as an unit test level.
test/drb/test_drbobject.rb tests DRbObject class as an unit test level.
test/drb/test_drb.rb tests druby protocol as an integration test level.
test/drb/test_drbssl.rb tests drbssl protocol as an integration test level.
test/drb/test_drbunix.rb is tests drbunix protocol as an integration test level.

So, I created test/drb/test_ssl.rb to test DRb::DRbSSLSocket::SSLConfig in lib/drb/ssl.rb as an unit test level.

tool/create_certs.sh design decisions

The tool/create_certs.sh is inspired by ruby/rubygems#9678. The directory test/drb/fixtures to manage SSL key/cert files is inspired by ruby/openssl managing SSL keys in test/openssl/fixtures/pkey directory. ruby/openssl manages only key files, not certificate files. ruby/openssl is generating testing certificates from the keys in tests.

Testing in RubyCI servers

I plan to test this PR with RHEL 9 server (OpenSSL version is >= 3.5, but OpenSSL config disables PQC by default), which is the case of support_pqc_handshake? is false ,and OpenBSD server as I saw the following logic in DRbSSLService, test/drb/test_drbssl.rb.

    if RUBY_PLATFORM.match?(/openbsd/)
      config[:SSLMinVersion] = OpenSSL::SSL::TLS1_2_VERSION
      config[:SSLMaxVersion] = OpenSSL::SSL::TLS1_2_VERSION
    end

Edited: I confirmed the tests passed in RubyCI RHEL 9 and OpenBSD servers.

drbssl PQC tests

Single cert tests ML-DSA-65

This test with TestDRbSSLPQC and DRbSSLPQCService is inspired by my proof-of-concept "## drbssl (SSL) auto-generated ML-DSA-65 cert". Also closed to the TestDRbSSLCore and DRbSSLService.

Multi cert tests ML-DSA-65/RSA

This test is inspired by my proof-of-concept "drbssl (SSL) pre-generated ML-DSA-65/RSA multi cert with client cert" case, and also inspired by ruby/openssl test/openssl/test_ssl.rb test_pqc_sigalg (https://github.com/ruby/openssl/blob/9796ee8f47003ec78fd8e052bc8dd6d1fcb0ae2b/test/openssl/test_ssl.rb#L2097).

PQC multi cert tests are executed via the following classes.

test/drb/test_drbssl.rb
- TestDRbSSLPQCMultiCertMLDSA65, DRbSSLPQCMultiCertMLDSA65Service
- TestDRbSSLPQCMultiCertRSA, DRbSSLPQCMultiCertRSAService
test/drb/ut_drb_drbssl_pqc_multi_cert.rb

It is hard to understand the testing framework in test/drb.

In DRbSSLPQCMultiCertMLDSA65Service, there are manager_config and client_config. manager_config is to manage the config used in manager to manage a child process ut_drb_drbssl_pqc_multi_cert.rb in this case. The main test workflow is between the server test/drb/ut_drb_drbssl_pqc_multi_cert.rb and client with client_config part. Client with client_config connects to the server ut_drb_drbssl_pqc_multi_cert.rb. However, it seems the ut_drb_drbssl_pqc_multi_cert.rb's config is also used as a client to connect to the server manager_config.

junaruga · 2026-07-29T10:40:26Z

I see the following CI failure. Let me fix it.

https://github.com/ruby/drb/actions/runs/30444292244/job/90550763624?pr=53

junaruga · 2026-07-30T18:27:23Z

I see the following CI failure. Let me fix it.

https://github.com/ruby/drb/actions/runs/30444292244/job/90550763624?pr=53

The cause of the CI failure was that OpenSSL::PKey::PKey#public_to_der didn't exist in openssl gem included in Ruby 2.7.0. It seems the method was added in openssl gem 2.2.0. I am not sure what the openssl gem version is in Ruby 2.7.0, as I couldn't find constant variable OpenSSL::VERSION in the openssl gem.

https://github.com/ruby/openssl/blob/v2.2.0/History.md?plain=1#L72-L75

Now use OpenSSL::PKey::RSA#public_key as before in RSA case.

cert.public_key = pkey.public_key

And use the following logic in ML-DSA-NN case.

cert.public_key = OpenSSL::PKey.read(pkey.public_to_der)

junaruga · 2026-07-30T19:41:36Z

I plan to test this PR with RHEL 9 server (OpenSSL version is >= 3.5, but OpenSSL config disables PQC by default), which is the case of support_pqc_handshake? is false ,and OpenBSD server as I saw the following logic in DRbSSLService, test/drb/test_drbssl.rb.

I tested this PR in RubyCI's RHEL 9 and OpenBSD servers.

In RHEL 9 server, I confirmed the tests passed. The ML-DSA tests are successfully omitted by support_pqc_handshake? in test/drb/drbtest.rb.

In OpenBSD server, I confirmed the tests passed as well. The used OpenSSL version was LibreSSL 4.3.0.

In DRbSSLService#start, test/drb/test_drbssl.rb, there is the following logic as I mentioned.

    if RUBY_PLATFORM.match?(/openbsd/)
      config[:SSLMinVersion] = OpenSSL::SSL::TLS1_2_VERSION
      config[:SSLMaxVersion] = OpenSSL::SSL::TLS1_2_VERSION
    end

I was not sure if DRbSSLPQCService#start, DRbSSLPQCMultiCertMLDSA65Service#start and DRbSSLPQCMultiCertRSAService#start needs the openbsd guard logic as well.

However, TestDRbSSLPQC, TestDRbSSLPQCMultiCertMLDSA65 and TestDRbSSLPQCMultiCertRSA skip OpenBSD's LibreSSL case by omit_unless_support_pqc in #setup before executing DRbSSLPQCService#start, DRbSSLPQCMultiCertMLDSA65Service#start and DRbSSLPQCMultiCertRSAService#start. So, we don't need the openbsd guard to these new 3 classes, DRbSSLPQCService, DRbSSLPQCMultiCertMLDSA65Service and DRbSSLPQCMultiCertRSAService.

junaruga · 2026-07-30T20:01:53Z

@seki or other maintainers, I updated notes section on the first comment. This PR is ready to review. I would appreciate your reviews.

junaruga · 2026-07-30T20:13:08Z

@rhenium I would appreciate your review for this PR as Ruby OpenSSL (openssl gem) maintainer.

junaruga · 2026-07-31T08:04:08Z

+# drbssl server with pre-generated ML-DSA-65/RSA multi cert and client cert
+
+require_relative 'ut_drb'
+require_relative 'drbtest_utils'


Previously, this file required require_relative 'drbtest' here. However, I got the following errors. The test result was 0 failures, 0 errors. But you see the RuntimeError tracktrace logs in test/drb/ut_drb_drbssl_pqc_multi_cert.rb. The cause was test/drb/drbtest.rb requiring test-unit via require 'test/unit'. It seems that the test-unit's at_exit calling Test::Unit::AutoRunner.run below was triggered when the child process exited, and caused errors when DRbTests::TestDRbSSLPQCMultiCertMLDSA65 and DRbTests::TestDRbSSLPQCMultiCertRSA were executed. So, now this file requires require_relative 'drbtest_utils' which doesn't require test-unit.

https://github.com/test-unit/test-unit/blob/3.7.8/lib/test/unit.rb#L516-L519

$ bundle exec ruby -I test/lib -rhelper test/drb/test_drbssl.rb -v Loaded suite test/drb/test_drbssl Started DRbTests::TestDRbSSLAry: test_01: .: (0.413258) test_02_collect: .: (0.436087) test_03_redo: .: (0.433541) test_05_break: .: (0.435188) test_06_next: .: (0.389877) test_07_break_18: .: (0.408441) DRbTests::TestDRbSSLCore: test_00_DRbObject: .: (0.419140) test_01: .: (0.509643) test_01_02_loop: .: (0.453699) test_02_basic_object: .: (0.380818) test_02_unknown: .: (0.421713) test_03: .: (0.417325) test_04: .: (0.416480) test_05_eq: .: (0.385149) test_06_timeout: .: (2.705462) test_07_private_missing: .: (0.422167) test_07_protected_missing: .: (0.451488) test_07_public_missing: .: (0.409648) test_07_send_missing: .: (0.544292) test_08_here: .: (0.382050) test_09_option: .: (0.420762) test_10_yield: .: (0.367299) test_10_yield_undumped: .: (0.408900) test_11_remote_no_method_error: .: (0.442798) DRbTests::TestDRbSSLPQC: test_01_hello: .: (0.326881) test_group_sigalg: .: (0.336463) DRbTests::TestDRbSSLPQCMultiCertMLDSA65: test_01_hello: .: (0.460257) test_group_sigalg: /home/jaruga/var/git/ruby/drb/test/drb/ut_drb_drbssl_pqc_multi_cert.rb:12:in 'shift': usage: /home/jaruga/var/git/ruby/drb/test/drb/ut_drb_drbssl_pqc_multi_cert.rb <manager-uri> <name> (RuntimeError) from /home/jaruga/.local/ruby-4.1.0-debug-3ef48ef9c8-openssl-4.1.0-7194354488/lib/ruby/4.1.0+1/optparse.rb:1735:in 'block in OptionParser#parse_in_order' from /home/jaruga/.local/ruby-4.1.0-debug-3ef48ef9c8-openssl-4.1.0-7194354488/lib/ruby/4.1.0+1/optparse.rb:1734:in 'Kernel#catch' from /home/jaruga/.local/ruby-4.1.0-debug-3ef48ef9c8-openssl-4.1.0-7194354488/lib/ruby/4.1.0+1/optparse.rb:1734:in 'OptionParser#parse_in_order' from /home/jaruga/.local/ruby-4.1.0-debug-3ef48ef9c8-openssl-4.1.0-7194354488/lib/ruby/4.1.0+1/optparse.rb:1728:in 'OptionParser#order!' from /home/jaruga/var/git/ruby/drb/vendor/bundle/ruby/4.1.0+1/gems/test-unit-3.7.8/lib/test/unit/autorunner.rb:201:in 'Test::Unit::AutoRunner#process_args' from /home/jaruga/var/git/ruby/drb/vendor/bundle/ruby/4.1.0+1/gems/test-unit-3.7.8/lib/test/unit/autorunner.rb:68:in 'Test::Unit::AutoRunner.run' from /home/jaruga/var/git/ruby/drb/vendor/bundle/ruby/4.1.0+1/gems/test-unit-3.7.8/lib/test/unit.rb:518:in 'block (2 levels) in <top (required)>' .: (0.479292) DRbTests::TestDRbSSLPQCMultiCertRSA: test_01_hello: .: (0.447127) test_group_sigalg: /home/jaruga/var/git/ruby/drb/test/drb/ut_drb_drbssl_pqc_multi_cert.rb:12:in 'shift': usage: /home/jaruga/var/git/ruby/drb/test/drb/ut_drb_drbssl_pqc_multi_cert.rb <manager-uri> <name> (RuntimeError) from /home/jaruga/.local/ruby-4.1.0-debug-3ef48ef9c8-openssl-4.1.0-7194354488/lib/ruby/4.1.0+1/optparse.rb:1735:in 'block in OptionParser#parse_in_order' from /home/jaruga/.local/ruby-4.1.0-debug-3ef48ef9c8-openssl-4.1.0-7194354488/lib/ruby/4.1.0+1/optparse.rb:1734:in 'Kernel#catch' from /home/jaruga/.local/ruby-4.1.0-debug-3ef48ef9c8-openssl-4.1.0-7194354488/lib/ruby/4.1.0+1/optparse.rb:1734:in 'OptionParser#parse_in_order' from /home/jaruga/.local/ruby-4.1.0-debug-3ef48ef9c8-openssl-4.1.0-7194354488/lib/ruby/4.1.0+1/optparse.rb:1728:in 'OptionParser#order!' from /home/jaruga/var/git/ruby/drb/vendor/bundle/ruby/4.1.0+1/gems/test-unit-3.7.8/lib/test/unit/autorunner.rb:201:in 'Test::Unit::AutoRunner#process_args' from /home/jaruga/var/git/ruby/drb/vendor/bundle/ruby/4.1.0+1/gems/test-unit-3.7.8/lib/test/unit/autorunner.rb:68:in 'Test::Unit::AutoRunner.run' from /home/jaruga/var/git/ruby/drb/vendor/bundle/ruby/4.1.0+1/gems/test-unit-3.7.8/lib/test/unit.rb:518:in 'block (2 levels) in <top (required)>' .: (0.482582) Finished in 15.021564814 seconds. --------------------------------------------------------------------------------------------------- 30 tests, 88 assertions, 0 failures, 0 errors, 0 pendings, 0 omissions, 0 notifications 100% passed --------------------------------------------------------------------------------------------------- 2.00 tests/s, 5.86 assertions/s

DRb::DRbSSLSocket::SSLConfig already works with pre-generated ML-DSA cert/key by :SSLCertificate and :SSLPrivateKey config options. This commit adds the following features in PQC use cases to #setup_certificate and #setup_ssl_context. * Add :SSLCertificates config option accepting an Array of [certificate, private_key] pairs for dual/multiple certificate support via OpenSSL::SSL::SSLContext#add_certificate changing from OpenSSL::SSL::SSLContext#cert and #key. Because an SSL server that accepts clients with either ML-DSA-NN or RSA certificates is useful in the use case of PQC migration from RSA (non-PQC) to ML-DSA (PQC). :SSLCertificate and :SSLPrivateKey are available for backward compatibility. But use OpenSSL::SSL::SSLContext#add_certificate internally. This is a behavior change. * Add :SSLPrivateKeyAlgorithms option accepting an Array of key algorithms (RSA, ML-DSA-44, ML-DSA-65, ML-DSA-87) for multi-certificate generation, defaulting to ["RSA"] for backward compatibility. * Add :SSLGroups option to control key exchange group such as ML-KEM in PQC. * Add :SSLSignatureAlgorithms, :SSLClientSignatureAlgorithms to control signature algorithms such as ML-DSA-NN in PQC, and RSA in non-PQC. * Add tool/create_certs.sh to generate test/drb/fixtures/*.{crt,key} to test with pre-generated certs/keys and add DRbTests::Fixtures module to read the certs/keys. * Add test/drb/test_ssl.rb to test lib/drb/ssl.rb as an unit test level. This approach aligns with test/drb/test_acl.rb to test lib/drb/acl.rb as an unit test level. * Add TestDRbSSLPQC, TestDRbSSLPQCMultiCertMLDSA65, TestDRbSSLPQCMultiCertRSA in test/drb/test_drbssl.rb. TestDRbSSLPQC is to test single PQC ML-KEM/ML-DSA server via test/drb/ut_drb_drbssl_pqc.rb. The testing class is inspired by TestDRbSSLCore. TestDRbSSLPQCMultiCertMLDSA65 and TestDRbSSLPQCMultiCertRSA are to test ML-DSA-65 (PQC) and RSA (non-PQC) dual (multiple) certificate server with client certificate via test/drb/ut_drb_drbssl_pqc_multi_cert.rb. The test is designed for a high-security use case with :SSLVerifyMode OpenSSL::SSL::VERIFY_PEER | OpenSSL::SSL::VERIFY_FAIL_IF_NO_PEER_CERT. Assisted-by: Claude:claude-opus-4-6[1m]

junaruga · 2026-07-31T20:51:25Z

I added and updated the code comments.

junaruga · 2026-08-01T07:45:54Z

+      [true, nil]
+    end
+  end
+end


I want to simplify the above tests TestDRbSSLPQC, TestDRbSSLPQCMultiCertMLDSA65 and TestDRbSSLPQCMultiCertRSA. These class designs align with the existing TestDRbSSL. However, I am not sure how much important or practical the current two-ways server client tests between manger and ut_*.rb to achieve both client (manager) connection to server (ut_*.rb) and client (ut_*.rb) connection to server (manager) via TestDRbSSL are. It's hard to understand and maintain the code.

Is it better just to create test_* without child classes of DRbService and ut_*.rb with the simple one-way server/client connection like run_drbssl_server_multi_cert_mldsa65_rsa_client_cert_pre_generated.rb and run_drbssl_client_multi_cert_mldsa65_rsa_client_cert_pre_generated.rb?

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Adding post-quantum cryptography (PQC) support #52

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junaruga marked this pull request as draft July 29, 2026 10:40

junaruga commented Jul 29, 2026

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junaruga marked this pull request as ready for review July 30, 2026 19:41

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Add post-quantum cryptography (PQC) support to SSLConfig - #53

Add post-quantum cryptography (PQC) support to SSLConfig#53
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Proof of concept

Commit message

Notes

CI cases supporting PQC

test/drb/test_ssl.rb testing lib/drb/ssl.rb as an unit test level

tool/create_certs.sh design decisions

Testing in RubyCI servers

drbssl PQC tests

Single cert tests ML-DSA-65

Multi cert tests ML-DSA-65/RSA

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