Document RSA-PSS signing for TLS 1.3 RSA client authentication - #43
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The "TLS 1.3 and X.509 Updates" section covered RSA-PSS signature verification only, which is the server-facing half: it lets a TLS 1.3 client check the CertificateVerify sent by a server presenting an RSA certificate. eclipse-threadx/netxduo#399 adds the signing half, so a client holding an RSA certificate can authenticate itself when the server asks for one. Document it: the rsa_pss_rsae_sha256 scheme the client selects and why RFC 8446 mandates it, that no application change is needed beyond the usual nx_secure_tls_local_certificate_add(), what happens when the server does not advertise the scheme, the two other rsae schemes the encoding handles, and the two limits - RSASSA-PSS certificates are out of scope, and signing keys are capped at 4096 bits. The claim that TLS 1.3 RSA certificate support was already complete moved to the new paragraph, since signing was the part still missing.
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Summary
The "TLS 1.3 and X.509 Updates" section of
netx-duo-secure-tls/chapter2.adocdocuments RSA-PSS signature verification only — the half that lets a TLS 1.3 client check the CertificateVerify sent by a server presenting an RSA certificate (eclipse-threadx/netxduo#377).eclipse-threadx/netxduo#399 adds the signing half, so a client holding an RSA certificate can authenticate itself when the server requests a client certificate. This PR documents it, as requested in eclipse-threadx/netxduo#399 (comment).
Changes
rtos-docs/netx-duo/modules/ROOT/pages/netx-duo-secure-tls/chapter2.adoc, section "TLS 1.3 and X.509 Updates":rsa_pss_rsae_sha256scheme (0x0804) the client selects and why RFC 8446 §9.1 makes it mandatory to implement, the salt length required by §4.2.3, that no application change is needed beyond the usualnx_secure_tls_local_certificate_add(), and theNX_SECURE_TLS_UNSUPPORTED_CERT_SIGN_ALGbehaviour when the server does not advertise the scheme.rsa_pss_rsae_sha384/sha512are handled by the CertificateVerify encoding, RSASSA-PSS certificates (rsa_pss_pss_*, 0x0809–0x080B) are out of scope, and signing keys are capped at 4096 bits.Text only — no structural or build changes.
Related: eclipse-threadx/netxduo#399, eclipse-threadx/netxduo#377