Create EC keys with TPM capabilities matching object attributes

[LinuxJedi]

EC keys generated on a TPM slot were created with a sign-only ECDSA template through the crypto callback, which the TPM will not accept for ECDH. The software copy of a TPM key holds only the public point, so it does not carry the private scalar the agreement needs either. A recent wolfSSL change to shared secret validation surfaced this in CI.

Create generated EC keys directly on the TPM with capabilities matching the object attributes: CKA_SIGN maps to the TPM sign attribute and CKA_DERIVE to the decrypt attribute that TPM2_ECDH_ZGen requires, with the null scheme when both are set. The crypto callback key generation is no longer used as it only creates signing keys. Curves the TPM does not support still fall back to software generation.

Compute ECDH for TPM-resident keys with TPM2_ECDH_ZGen. Keys created without the decrypt attribute, from a store written before derive support, return an error as the TPM will not perform ECDH with them.

Also clear crypto callback key references when freeing an object so the callback cannot act on freed memory, and have the ECDH tests check the derived secret so an incomplete agreement is caught.

[Copilot]

Pull request overview

This PR fixes TPM-backed EC key generation and ECDH behavior so keys created on a TPM slot have TPM capabilities that match PKCS#11 object attributes (sign vs derive), and ECDH for TPM-resident keys is performed inside the TPM to avoid deriving with missing private material.

Changes:

• Generate supported EC keys directly on the TPM with sign/decrypt attributes derived from CKA_SIGN/CKA_DERIVE, falling back to software for unsupported curves.
• Compute ECDH for TPM-resident keys via TPM2_ECDH_ZGen, and error out for older sign-only TPM keys that lack the decrypt attribute.
• Harden cleanup and tests: clear TPM crypto-callback key references on object free, and add an ECDH test check to catch “derived secret is all zeros” failures.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
tests/pkcs11test.c	Adds a guard in the ECDH test to fail if the derived secret is all zeros (catches incomplete/invalid derive behavior).
src/internal.c	Implements TPM EC keypair generation with attribute-matched capabilities, TPM-based ECDH using TPM2_ECDH_ZGen, and clears TPM callback key references during object free.

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