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romanett
d552634258
Closes #4510. ## Summary OPC UA Part 6 feeds the **raw** ECDH shared secret into HKDF. .NET Framework only exposes `ECDiffieHellman.DeriveKeyMaterial`, which always hashes it, so the ECC SecureChannel and user-token policies were unavailable on `net48` (`SecurityPolicies.GetInfo` returned `null`). This adds a BouncyCastle polyfill for just that primitive: - **`Opc.Ua.Security.Certificates/Org.BouncyCastle/EcdhRawAgreement.cs`** (`net48` only): an internal `DeriveRawSecretAgreement(this ECDiffieHellman, ECDiffieHellmanPublicKey)` extension using `ECDHBasicAgreement`. It returns the X coordinate padded to the field size, exactly like the .NET 8 BCL method. Keys stay CNG keys; ECDSA signatures and HKDF stay on the platform — only the agreement step is managed code. The point is validated (on curve, not infinity) and mismatched curves are rejected. - Because the extension mirrors the .NET 8 signature, `Nonce.GenerateSecret` now has one code path on every target. - `SupportsRawEccSecretAgreement()` is removed; the CBC-based ECC policies (`ECC_nistP256`, `ECC_nistP384`, `ECC_brainpoolP256r1`, `ECC_brainpoolP384r1`) are offered on every target (still subject to OS curve support). - BouncyCastle was already a `net48` dependency of `Opc.Ua.Security.Certificates`; no new package. (Only `net48` is downlevel now — `netstandard2.1`/`net472` from the issue text are no longer targets.) **Not in scope:** the `_AesGcm` / `_ChaChaPoly` ECC variants (and PubSub DTLS) still need .NET 8 because .NET Framework has no AEAD ciphers — follow-up stacked on this branch. ## Docs `EccProfiles.md` (Known limitations), `migrate/2.0.x/certificates.md`, `ProductionChecklist.md`, `Profiles.md`, `WhatsNewIn2.0.md`. Calls out that on `net48` the agreement step does not run in a FIPS/validated module. ## Tests (local) | Suite | Result | |---|---| | `Opc.Ua.Core.Tests` full, net48 | 5956 passed, 0 failed | | `EccInteropTests` net48 vs 1.5.378 peer (net8.0, native raw ECDH) | 26 passed; 28 skipped (AEAD + curve25519/448) — all four CBC curves, both directions, UserName tokens, token renewal | | `Opc.Ua.Sessions.Tests` ECC filter, net48 | 52 passed, 0 failed | | Server `SessionCoverageTests`/`EphemeralNonce*`, Configuration builder tests, net48 | all pass | | Nonce/ECC/EncryptedSecret + session tests, net10.0 | all pass | New tests: symmetric agreement on all four curves; on net48 an oracle against CNG (`SHA256(raw) == DeriveKeyFromHash`); curve mismatch and off-curve rejection. Tests that asserted the old net48 limitation were updated. 🤖 Generated with [Claude Code](https://claude.com/claude-code) --------- Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>