test_x25519_ecdh: 実際の SE050 ECDH 計算テストを追加

Test 5 を実装して、SE050 ハードウェア接続時の実際の ECDH 計算を検証:

実装内容:
- I2C HAL 初期化と SE050 接続
- Session/Keystore/RNG の初期化
- Alice と Bob の鍵ペア生成 (se050_x25519_generate_keypair)
- Alice: ECDH(Bob_pub, Alice_priv) 計算
- Bob: ECDH(Alice_pub, Bob_priv) 計算
- 共有秘密の一致確認

動作:
- SE050 未接続：SKIP (構造テストは Test 3 で完了)
- SE050 接続時：実際の ECDH 計算と共有秘密の一致を検証

エラーハンドリング:
- I2C 接続失敗： gracefully skip
- セッション作成失敗： gracefully skip
- 鍵生成失敗： fail
- ECDH 計算失敗： fail
- 共有秘密不一致： fail

テスト結果:
- SE050 未接続環境：6/6 PASS (Test 5 は SKIP)
- SE050 接続環境：実際の ECDH 計算を検証可能

tests/test_x25519_ecdh.c

@@ -185,17 +185,133 @@ static int test_rfc7748_vectors(void)
     return 1;
 }
 
-/* Test 5: Cross-compatibility */
+/* Test 5: Cross-compatibility with actual SE050 ECDH */
 static int test_cross_compatibility(void)
 {
-    printf("\n=== Test 5: Cross-Compatibility Check ===\n");
+    se050_i2c_hal_t hal;
-    printf("[INFO] Alice computes: ECDH(Bob_pub, Alice_priv)\n");
+    se050_session_ctx_t *session;
-    printf("[INFO] Bob computes: ECDH(Alice_pub, Bob_priv)\n");
+    se050_keystore_ctx_t *keystore;
-    printf("[INFO] Both should get same shared secret\n");
+    se050_rng_ctx_t *rng;
-    printf("[PASS] Cross-compatibility structure verified\n");
+    se050_status_t status;
-    printf("[INFO] Actual computation requires SE050 hardware\n");
+    uint8_t shared_secret_alice[32];
+    uint8_t shared_secret_bob[32];
+    int result = 1;
+    
+    printf("\n=== Test 5: Cross-Compatibility Check (SE050 ECDH) ===\n");
+    
+    /* Check if hardware is available */
+    printf("[INFO] Attempting to connect to SE050...\n");
+    
+    /* Initialize I2C HAL */
+    status = se050_i2c_init(&hal, "/dev/i2c-1", 0x48);
+    if (status != SE050_OK) {
+        printf("[SKIP] SE050 not available at /dev/i2c-1 (0x48)\n");
+        printf("[INFO] For hardware test, ensure SE050 is connected\n");
+        printf("[INFO] Structure verification passed (see Test 3)\n");
+        return 1;  /* Skip, not fail */
+    }
+    
+    printf("[INFO] I2C connection established\n");
+    
+    /* Create session */
+    status = se050_session_create(&session, &hal);
+    if (status != SE050_OK) {
+        printf("[SKIP] Session creation failed (0x%04x)\n", status);
+        se050_i2c_close(&hal);
+        return 1;  /* Skip, not fail */
+    }
+    printf("[INFO] Session created\n");
+    
+    /* Initialize keystore */
+    status = se050_keystore_init(&keystore, session);
+    if (status != SE050_OK) {
+        printf("[SKIP] Keystore init failed (0x%04x)\n", status);
+        se050_session_delete(session);
+        se050_i2c_close(&hal);
         return 1;
     }
+    printf("[INFO] Keystore initialized\n");
+    
+    /* Initialize RNG */
+    status = se050_rng_init(&rng, session);
+    if (status != SE050_OK) {
+        printf("[SKIP] RNG init failed (0x%04x)\n", status);
+        se050_keystore_free(keystore);
+        se050_session_delete(session);
+        se050_i2c_close(&hal);
+        return 1;
+    }
+    printf("[INFO] RNG initialized\n");
+    
+    /* Generate Alice's keypair */
+    se050_x25519_keypair_t keypair_alice;
+    status = se050_x25519_generate_keypair(keystore, &keypair_alice, 0x1001);
+    if (status != SE050_OK) {
+        printf("[SKIP] Alice key generation failed (0x%04x)\n", status);
+        result = 0;
+        goto cleanup;
+    }
+    printf("[INFO] Alice's keypair generated (ID: 0x1001)\n");
+    
+    /* Generate Bob's keypair */
+    se050_x25519_keypair_t keypair_bob;
+    status = se050_x25519_generate_keypair(keystore, &keypair_bob, 0x1002);
+    if (status != SE050_OK) {
+        printf("[SKIP] Bob key generation failed (0x%04x)\n", status);
+        result = 0;
+        goto cleanup;
+    }
+    printf("[INFO] Bob's keypair generated (ID: 0x1002)\n");
+    
+    /* Alice computes shared secret using Bob's public key */
+    printf("[INFO] Alice computing ECDH with Bob's public key...\n");
+    status = se050_x25519_compute_shared_secret(keystore, 0x1001,
+                                                  keypair_bob.public_key,
+                                                  shared_secret_alice);
+    if (status != SE050_OK) {
+        printf("[FAIL] Alice ECDH computation failed (0x%04x)\n", status);
+        result = 0;
+        goto cleanup;
+    }
+    printf("[INFO] Alice's shared secret computed\n");
+    
+    /* Bob computes shared secret using Alice's public key */
+    printf("[INFO] Bob computing ECDH with Alice's public key...\n");
+    status = se050_x25519_compute_shared_secret(keystore, 0x1002,
+                                                  keypair_alice.public_key,
+                                                  shared_secret_bob);
+    if (status != SE050_OK) {
+        printf("[FAIL] Bob ECDH computation failed (0x%04x)\n", status);
+        result = 0;
+        goto cleanup;
+    }
+    printf("[INFO] Bob's shared secret computed\n");
+    
+    /* Compare shared secrets */
+    printf("[INFO] Comparing shared secrets...\n");
+    printf("[INFO] Alice's shared secret:\n");
+    print_hex("  ", shared_secret_alice, 32);
+    printf("[INFO] Bob's shared secret:\n");
+    print_hex("  ", shared_secret_bob, 32);
+    
+    if (!buffers_equal(shared_secret_alice, shared_secret_bob, 32)) {
+        printf("[FAIL] Shared secrets DO NOT match!\n");
+        result = 0;
+        goto cleanup;
+    }
+    
+    printf("[PASS] Shared secrets match! ECDH successful.\n");
+    printf("[INFO] Alice and Bob now share a common secret for WireGuard.\n");
+
+cleanup:
+    /* Cleanup */
+    se050_rng_free(rng);
+    se050_keystore_free(keystore);
+    se050_session_delete(session);
+    se050_i2c_close(&hal);
+    
+    return result;
+}
 
 /* Test 6: Key material security */
 static int test_key_material_security(void)