Add TLS 1.3 group information to various SSL/TLS methods and classes

As we move toward post quantum crypto, selecting and/or detecting hybrid TLS 1.3 groups (ie; Eliptic Curve Crypto [ECC] + MLKEM) is paramount.

Today, this data is not exposed through various .NET methods, such as the ASP.NET code below.

app.MapGet("/", (HttpContext ctx) =>
{
    var tls = ctx.Features.Get<ITlsHandshakeFeature>();
    return Results.Json(new
    {
        Protocol = tls?.Protocol.ToString() ?? "Unknown",
        CipherSuite = tls?.NegotiatedCipherSuite?.ToString() ?? "Unknown"
    });
});

An update would include some like this:

        CipherGroup = tls?.NegotiatedGroup?.ToString() ?? "Unknown"

This would require additional pub enums that include the group value:

    public enum TlsSupportedGroup : ushort
    {
        // Classical ECDHE (RFC 8446 §4.2.7, RFC 8422).
        secp256r1 = 0x0017,   // NIST P-256
        secp384r1 = 0x0018,   // NIST P-384
        x25519    = 0x001D,   // RFC 7748
 
        // Hybrid ECDHE + ML-KEM (draft-kwiatkowski-tls-ecdhe-mlkem).
        SecP256r1MLKEM768  = 0x11EB,
        X25519MLKEM768     = 0x11EC,
        SecP384r1MLKEM1024 = 0x11ED,
    }

This list is not complete, but I doubt you want the entire list; it runs to about 100-ish values.

For bonus points; the following would be useful:

IsHybrid() - classic AND MLKEM
IsPostQuantum() - MLKEM OR IsHybrid()
IsPurePostQuantum() - MLKEM
IsClassic()  - classic

Note: the group is negotiated separately from the ciphersuite in TLS 1.3.

If you want more info - just ask.

Tagging subscribers to this area: @dotnet/area-system-runtime
See info in area-owners.md if you want to be subscribed.

@bartonjs

Tagging subscribers to this area: @dotnet/ncl, @bartonjs, @vcsjones
See info in area-owners.md if you want to be subscribed.

Personally, I think exposing the negotiated value for the TLS Supported Group is goodness (ideally using the wire value, a la ciphersuites). But I'd leave out the policy/judgment/classification "IsHybrid", etc. Names like "IsClassic" or "IsTraditional" don't age well.

Also, looks like the hybrid PQC exchanges are no longer draft, they're now IETF RFC 10024 (as of two days ago)

Triage: too late for 11.0, but given how the space evolves, we should look at it for 12.0

It seems that the only platform that surfaces the algorithm is currently OpenSSL, I don't see a way to access it on the other platforms. Shipping a new property that gives useful information only on a single platform is difficult, so we hold off until there is support at least for Schannel.

Pushed a feasibility prototype branch exploring exposing the negotiated TLS 1.3 supported group (named/key-exchange group, including hybrid PQC groups such as X25519MLKEM768):

Branch: https://github.com/rzikm/dotnet-runtime/tree/rzikm/tls-negotiated-group

Highlights:

New [CLSCompliant(false)] public enum TlsSupportedGroup : ushort using IANA wire code points, generated from the IANA registry via a T4 template (same technique as TlsCipherSuite).
New SslStream.NegotiatedGroup property plumbed through per-platform SslConnectionInfo.
OpenSSL implementation via SSL_get_negotiated_group (3.0+), mapping NID -> IANA value (provider/unknown groups carry the IANA id in the low bits).

Platform feasibility (verified against primary sources): only OpenSSL exposes the negotiated group.

Windows/Schannel - no QueryContextAttributes attribute returns it (szExchange/aiExch give only the key-exchange algorithm), still true on 24H2/Server 2025.
macOS/Network.framework - sec_protocol_metadata exposes ciphersuite + protocol only.
Android/JSSE+Conscrypt - no public accessor.

On these platforms the property reports 0 (unavailable), mirroring how NegotiatedCipherSuite is platform-gated. This is unapproved public API - the branch is prototype/evidence for API review, not a PR.

Note

This comment was generated with the assistance of GitHub Copilot.

Navigation Menu

Repository navigation

Add TLS 1.3 group information to various SSL/TLS methods and classes #132239

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Add TLS 1.3 group information to various SSL/TLS methods and classes #132239

Description

Activity

dotnet-policy-service commented on Aug 12, 2026

dotnet-policy-service commented on Aug 12, 2026

bartonjs commented on Aug 12, 2026

rzikm commented on Aug 13, 2026

rzikm commented on Aug 26, 2026

rzikm commented on Aug 27, 2026

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions