nx_x509_chain_verify.nx

nx_x509_chain_verify.nx -- walk an X.509 cert chain leaf-to-root. Phase 0b §I.4 piece 7 of the chain-walker arc. THE primitive that turns the substrate's single-cert verify (verify_under_issuer, commit 927d9d47) into a real Web PKI chain validator. Composes: nx_x509_verify_under_issuer.nx -- per-cert sig verify nx_x509_dn_match.nx -- DN byte-equality nx_x509_leaf_check.nx (caller) -- separate; caller invokes first for leaf cert's validity + SAN. Chain model: caller prepares an array of parsed X509Cert pointers + their backing buffers, in order from leaf to root: certs[0] = leaf cert (server identity) certs[1] = first intermediate (signed leaf) certs[..] = more intermediates certs[n-1] = trust anchor (root CA, treated as self-signed for the chain-walker purpose -- caller has separately confirmed it lives in the trusted root set) For each adjacent (child, parent) pair (i, i+1): 1. DN linkage: child.issuer must byte-equal parent.subject 2. Sig verify: child's outer sig verifies under parent's pubkey The final cert (trust anchor) is NOT verified against anything further -- the caller's responsibility to ensure it's actually in the trusted root set. RFC 5280 §6.1 calls this the "trust anchor input" to path validation. Public API: nx_x509_chain_verify(bufs, certs, n) -> verdict bufs[i] = *u8 to cert[i]'s DER buffer certs[i] = *X509Cert parsed from bufs[i] n = number of certs in the chain (>=1) nx_x509_chain_verdict_is_valid(v) -> 0|1 Sealed verdict enum: