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 6## Add the dynamic library in the CMake script. 7```txt 8 target_link_libraries(entry PUBLIC libhuks_ndk.z.so) 9``` 10 11## How to Develop 12 131. Set parameters. 14 - **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. 15 - **paramSetIn**: This parameter is reserved. Leave it empty. 16 - **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. 17 182. Use [OH_Huks_GetKeyItemParamSet](../../reference/apis-universal-keystore-kit/_huks_key_api.md#oh_huks_getkeyitemparamset) to obtain key properties. 19 203. Check the return value. If the operation is successful, obtain the key properties from **paramSetOut**. If the operation fails, an error code is returned. 21 22```c++ 23#include "huks/native_huks_api.h" 24#include "huks/native_huks_param.h" 25#include <string.h> 26static napi_value GetKeyParamSet(napi_env env, napi_callback_info info) 27{ 28 /* 1. Set the key alias. */ 29 const char *alias = "test_key"; 30 struct OH_Huks_Blob aliasBlob = { .size = (uint32_t)strlen(alias), .data = (uint8_t *)alias }; 31 /* Request memory for outParamSet. */ 32 struct OH_Huks_ParamSet *outParamSet = (struct OH_Huks_ParamSet *)malloc(512); // Request memory based on service requirements. 33 if (outParamSet == nullptr) { 34 return nullptr; 35 } 36 outParamSet->paramSetSize = 512; 37 struct OH_Huks_Result ohResult; 38 do { 39 /* 2. Obtain the key properties. */ 40 ohResult = OH_Huks_GetKeyItemParamSet(&aliasBlob, nullptr, outParamSet); 41 if (ohResult.errorCode != OH_HUKS_SUCCESS) { 42 break; 43 } 44 /* 3. Read key properties from outParamSet. For example, obtain OH_HUKS_TAG_PURPOSE. */ 45 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. 46 ohResult = OH_Huks_GetParam(outParamSet, OH_HUKS_TAG_PURPOSE, &purposeParam); 47 if (ohResult.errorCode != OH_HUKS_SUCCESS) { 48 break; 49 } 50 } while (0); 51 OH_Huks_FreeParamSet(&outParamSet); 52 napi_value ret; 53 napi_create_int32(env, ohResult.errorCode, &ret); 54 return ret; 55} 56``` 57