crypto/tls: support RA-TLS challenge extension in ClientHello#77714
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crypto/tls: support RA-TLS challenge extension in ClientHello#77714bfoing wants to merge 1 commit intogolang:release-branch.go1.25from
bfoing wants to merge 1 commit intogolang:release-branch.go1.25from
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Parse the RA-TLS challenge from the ClientHello extensions (extension code temporarily set to 0xffbb) and expose it via ClientHelloInfo.RATLSChallenge, allowing server-side callbacks (GetConfigForClient, GetCertificate) to access the attestation challenge during the TLS handshake. The extension is optional and server-side only (unmarshal only, no marshal). The challenge payload is validated to be between 8 and 64 bytes; malformed or out-of-range values cause the handshake to fail. Concept: https://www.rfc-editor.org/rfc/rfc9334.html
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This PR should only be considered once the real IANA value is assigned for the RA-TLS extension. See the TODO comment on
extensionRATLSinsrc/crypto/tls/common.goI open it so that early adopters of RA-TLS can look at / use the fork in the mean time.
Summary
This adds server-side support for the Remote Attestation TLS (RA-TLS) challenge extension, as defined in the RFC-9334.
When a TLS client includes the RA-TLS extension in its ClientHello, the server can read the challenge bytes and use them to generate a platform-specific attestation evidence (e.g. an Intel TDX) that is bound to the TLS handshake.
Changes
src/crypto/tls/common.goextensionRATLSconstant (0xffbb) andRATLSChallenge []bytefield toClientHelloInfosrc/crypto/tls/handshake_messages.goraTLSChallengefield toclientHelloMsgand unmarshal logic with 8–64 byte length validationsrc/crypto/tls/handshake_server.goraTLSChallengefromclientHelloMsgintoClientHelloInfosrc/crypto/tls/handshake_messages_test.goTestRATLSChallengeExtension(8 subtests)Design decisions
need to send this extension; it is consumed by the server to produce
attestation evidence via
GetConfigForClientorGetCertificatecallbacks.out-of-range payloads are rejected during unmarshal (handshake fails).
0xffbb: Temporary private-use value. Will bereplaced with the IANA-assigned code once the draft is finalized.
ClientHelloInfo.RATLSChallengeis
niland the handshake proceeds normally.Test coverage
TestRATLSChallengeExtensioncovers:ClientHelloInfo.RATLSChallengeReferences