Migrate CMAC_* to EVP_MAC interface

[VladGud]

Migrate CMAC_* to EVP_MAC interface

Issue Summary

Migrate the CMAC implementation in gost_omac.c from deprecated CMAC_* APIs to the modern EVP_MAC interface to ensure compatibility with OpenSSL builds that disable deprecated functionality.

Problem Description

The current OMAC (CMAC) implementation relies on deprecated CMAC APIs (CMAC_CTX_new, CMAC_CTX_free, CMAC_Init, CMAC_Update, CMAC_Final, CMAC_CTX_copy), which are marked for removal in future OpenSSL versions. This prevents the codebase from building or running with OPENSSL_NO_DEPRECATED_3_0 enabled. The migration to EVP_MAC provides a stable, provider-based alternative that aligns with OpenSSL's modern architecture.

Current Implementation

• OMAC_CTX structure contains CMAC_CTX *cmac_ctx
• Functions like omac_key(), omac_imit_update(), omac_imit_final(), omac_imit_copy(), and omac_imit_cleanup() directly use CMAC_* APIs
• Context initialization and cleanup rely on CMAC_CTX_new() and CMAC_CTX_free()
• MAC computation uses CMAC_Init(), CMAC_Update(), and CMAC_Final()

Required Changes

1. Replace CMAC_CTX with EVP_MAC context

• Modify OMAC_CTX to store EVP_MAC *mac and EVP_MAC_CTX *mac_ctx instead of CMAC_CTX *cmac_ctx
• Update structure initialization to use EVP_MAC_fetch("CMAC") and EVP_MAC_CTX_new()

2. Update MAC initialization and key setting

• In omac_key(), replace CMAC_Init() with EVP_MAC_init() using OSSL_MAC_PARAM_CIPHER parameter
• Ensure cipher is specified by name (e.g., c->cipher_name)

3. Update MAC update and final operations

• Replace CMAC_Update() with EVP_MAC_update()
• Replace CMAC_Final() with EVP_MAC_final(), writing output to a buffer and then memcpy to dgst_size

4. Update context copy and cleanup

• Replace CMAC_CTX_copy() with EVP_MAC_CTX_dup() (if available) or manual duplication
• Replace CMAC_CTX_free() with EVP_MAC_CTX_free() and EVP_MAC_free()

5. Handle EVP_MAC availability

• Add checks for EVP_MAC support; provide fallback or error if not available

Files to Modify

• gost_omac.c: Update OMAC_CTX structure, omac_key(), omac_imit_update(), omac_imit_final(), omac_imit_copy(), omac_imit_cleanup()
• Potentially gost_lcl.h: If OMAC_CTX is defined there, update accordingly

Acceptance Criteria

• CMAC implementation uses only EVP_MAC APIs, no CMAC_* calls remain
• OMAC operations (init, update, final, copy, cleanup) work correctly with EVP_MAC

Testing

• Unit tests for OMAC (magma_mac, grasshopper_mac) pass with new implementation