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 · 2026-07-31T20:51:25Z

I added and updated the code comments.

rhenium · 2026-08-01T19:07:57Z

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.

I won't be the one deciding whether to merge this, but I'm not really convinced there's much value in being able to set up a server with multiple self-signed certificates.

hsbt · 2026-08-06T08:22:32Z

@kou Could you review this? @junaruga introduced this work at today's Dev meeting.

I would appreciate it if you could review this, especially regarding the API changes such as the multiple certificates feature that was added in this PR.

kou · 2026-08-06T13:27:14Z

+
+ # Establish the OpenSSL::SSL::SSLContext with the configuration
+ # parameters provided.
+ def setup_ssl_context


Why do you want to make setup_ssl_context public? It's just for test? If so, we should not make it public. We can use __send__ in test.

In the current master branch 2b002d4, the setup_ssl_context is already public method. I didn't change the method from private to public.
drb/lib/drb/ssl.rb
Line 203 in 2b002d4
defsetup_ssl_context

@kou I am waiting for your response on this topic.

junaruga · 2026-08-12T16:10:41Z

Sorry for my late response. Thanks for your reviews. I will check the reviews and fix for them.

This commit fixes the following CI failures in Windows. I don't know why this change fixed. Perhaps Bundler's handling with git repository is different. https://github.com/ruby/drb/actions/runs/32029577375/job/95386338154?pr=54 ``` D:/a/drb/drb/test/lib/helper.rb:2:in 'Kernel#require': cannot load such file -- core_assertions (LoadError) from D:/a/drb/drb/test/lib/helper.rb:2:in '<top (required)>' from <internal:D:/rubyinstaller-head-x64/lib/ruby/4.1.0+4/rubygems/core_ext/kernel_require.rb>:139:in 'Kernel#require' rake aborted! Command failed with status (1) D:/a/drb/drb/vendor/bundle/ruby/4.1.0+4/gems/rake-13.4.2/exe/rake:27:in '<top (required)>' D:/rubyinstaller-head-x64/bin/bundle:33:in '<main>' Tasks: TOP => default => test (See full trace by running task with --trace) Error: Process completed with exit code 1. ```

OpenSSL::PKey::RSA#public_key is obsolete according to ruby/openssl#1092.

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 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.rb 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 at the unit test level. This approach aligns with test/drb/test_acl.rb to test lib/drb/acl.rb at the unit test level. * Add TestDRbSSLPQC, TestDRbSSLPQCMultipleCert in test/drb/test_drbssl.rb. TestDRbSSLPQC is to test single PQC ML-KEM/ML-DSA server and client. TestDRbSSLPQCMultipleCert is to test ML-DSA-65 (PQC) and RSA (non-PQC) multiple certificate server with client certificate verification. 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 · 2026-08-18T21:54:41Z

I rebased this PR, fixing the things mentioned by reviews.

First, I backed up the initial PR into my fork repository's wip/support-pqc-pr1 branch.

Now this PR has 3 commits.

The 1st commit is the same with #54 to pass the CI. I will remove this commit on this PR after #54 is merged or someone fixed the issue causing failing Windows CI cases.

The 2nd commit is for refactoring, which was mentioned in the review. But it is not related to this PR.

The 3rd commit is the main commit. I simplified the tests in test/drb/test_drbssl.rb without new service classes and test/drb/ut_*.rb files. I also simplified the omit_unless_support_pqc method in test/drb/drbtest.rb to align with the updated omit logic in the test/rubygems/pqc_utilities.rb.

Commit messages

The 2nd commit

Remove OpenSSL::PKey::RSA#public_key

OpenSSL::PKey::RSA#public_key is obsolete according to ruby/openssl#1092.

The 3rd commit (main commit)

Add post-quantum cryptography (PQC) support to SSLConfig

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 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.rb 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 at the unit test level.
This approach aligns with test/drb/test_acl.rb to test lib/drb/acl.rb
at the unit test level.
Add TestDRbSSLPQC, TestDRbSSLPQCMultipleCert in test/drb/test_drbssl.rb.
TestDRbSSLPQC is to test single PQC ML-KEM/ML-DSA server and client.
TestDRbSSLPQCMultipleCert is to test ML-DSA-65 (PQC) and RSA (non-PQC)
multiple certificate server with client certificate verification.
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 · 2026-08-18T22:06:05Z

@kou Could you review again? Thanks.
@rhenium Could you review again especially for OpenSSL logic parts? Thanks.

junaruga temporarily deployed to release July 29, 2026 10:35 — with GitHub Actions Inactive

junaruga mentioned this pull request Jul 29, 2026
Adding post-quantum cryptography (PQC) support #52
Open

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

junaruga commented Jul 29, 2026
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junaruga force-pushed the wip/support-pqc branch from 7e5fc39 to 2a55f51Compare July 30, 2026 18:15

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

junaruga commented Jul 31, 2026
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Comment threadtest/drb/ut_drb_drbssl_pqc_multi_cert.rb Outdated

junaruga force-pushed the wip/support-pqc branch from 2a55f51 to 692613dCompare July 31, 2026 13:31

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junaruga force-pushed the wip/support-pqc branch from 692613d to a3c95bcCompare July 31, 2026 20:49

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junaruga commented Aug 1, 2026
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Comment threadtest/drb/test_drbssl.rb

rhenium reviewed Aug 1, 2026
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kou reviewed Aug 6, 2026
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rhenium mentioned this pull request Aug 14, 2026
pkey: avoid using {DH,DSA,RSA}#public_key in docs and tests ruby/openssl#1092
Open

junaruga added 3 commits August 18, 2026 22:45

Remove OpenSSL::PKey::RSA#public_key
f83310f
OpenSSL::PKey::RSA#public_key is obsolete according to ruby/openssl#1092.

junaruga force-pushed the wip/support-pqc branch from a3c95bc to 328508fCompare August 18, 2026 21:45

junaruga deployed to release August 18, 2026 21:45 — with GitHub Actions Active

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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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The 2nd commit

The 3rd commit (main commit)

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