1# Obtaining Key Properties (C/C++)
2
3
4This topic describes how to obtain properties of a key. Before the operation, ensure that the key exists in HUKS.
5>**NOTE**<br>
6> The mini-system devices do not support the operation for obtaining key properties.
7
8## Add the dynamic library in the CMake script.
9```txt
10   target_link_libraries(entry PUBLIC libhuks_ndk.z.so)
11```
12
13## How to Develop
14
151. Set parameters.
16   - **keyAlias**: key alias encapsulated in an [OH_Huks_Blob](../../reference/apis-universal-keystore-kit/_o_h___huks___blob.md) struct. The maximum length of the key alias is 128 bytes.
17   - **paramSetIn**: This parameter is reserved. Leave it empty.
18   - **paramSetOut**: result set used to hold the key properties obtained. It is an object of the [OH_Huks_ParamSet](../../reference/apis-universal-keystore-kit/_o_h___huks___param_set.md) type. Ensure that there is enough memory for storing the key properties obtained.
19
202. Use [OH_Huks_GetKeyItemParamSet](../../reference/apis-universal-keystore-kit/_huks_key_api.md#oh_huks_getkeyitemparamset) to obtain key properties.
21
223. Check the return value. If the operation is successful, obtain the key properties from **paramSetOut**. If the operation fails, an error code is returned.
23
24```c++
25#include "huks/native_huks_api.h"
26#include "huks/native_huks_param.h"
27#include <string.h>
28static napi_value GetKeyParamSet(napi_env env, napi_callback_info info)
29{
30    /* 1. Set the key alias. */
31    const char *alias = "test_key";
32    struct OH_Huks_Blob aliasBlob = { .size = (uint32_t)strlen(alias), .data = (uint8_t *)alias };
33    /* Request memory for outParamSet. */
34    struct OH_Huks_ParamSet *outParamSet = (struct OH_Huks_ParamSet *)malloc(512); // Request memory based on service requirements.
35    if (outParamSet == nullptr) {
36        return nullptr;
37    }
38    outParamSet->paramSetSize = 512;
39    struct OH_Huks_Result ohResult;
40    do {
41        /* 2. Obtain the key properties. */
42        ohResult = OH_Huks_GetKeyItemParamSet(&aliasBlob, nullptr, outParamSet);
43        if (ohResult.errorCode != OH_HUKS_SUCCESS) {
44            break;
45        }
46        /* 3. Read key properties from outParamSet. For example, obtain OH_HUKS_TAG_PURPOSE. */
47        OH_Huks_Param *purposeParam = nullptr; // No memory needs to be requested. After the parameter is obtained, the pointer points to the memory address of the parameter in the parameter set.
48        ohResult = OH_Huks_GetParam(outParamSet, OH_HUKS_TAG_PURPOSE, &purposeParam);
49        if (ohResult.errorCode != OH_HUKS_SUCCESS) {
50            break;
51        }
52    } while (0);
53    OH_Huks_FreeParamSet(&outParamSet);
54    napi_value ret;
55    napi_create_int32(env, ohResult.errorCode, &ret);
56    return ret;
57}
58```
59