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1# 密钥导出(C/C++)
2
3<!--Kit: Universal Keystore Kit-->
4<!--Subsystem: Security-->
5<!--Owner: @wutiantian-gitee-->
6<!--Designer: @HighLowWorld-->
7<!--Tester: @wxy1234564846-->
8<!--Adviser: @zengyawen-->
9
10业务需要获取持久化存储的非对称密钥的公钥时使用，当前支持ECC/RSA/ED25519/X25519/SM2的公钥导出。
11
12>**说明：**
13> <!--RP1-->轻量级设备<!--RP1End-->仅支持RSA公钥导出。
14
15## 在CMake脚本中链接相关动态库
16```txt
17target_link_libraries(entry PUBLIC libhuks_ndk.z.so)
18```
19
20## 开发步骤
21
221. 构造对应参数。
23   - keyAlias：密钥别名，封装成[OH_Huks_Blob](../../reference/apis-universal-keystore-kit/capi-hukstypeapi-oh-huks-blob.md)结构，密钥别名最大长度为128字节。
24   - paramSetIn：预留参数，暂不需要处理，传空即可。
25   - key：用于放置导出的公钥，为[OH_Huks_Blob](../../reference/apis-universal-keystore-kit/capi-hukstypeapi-oh-huks-blob.md)类型对象，需要业务提前申请好内存，需申请足够容纳获取到的密钥属性集的内存大小。
26
272. 调用接口[OH_Huks_GetKeyItemParamSet](../../reference/apis-universal-keystore-kit/capi-native-huks-api-h.md#oh_huks_getkeyitemparamset)，传入上述参数。
28
293. 返回值为成功码/错误码，导出公钥以标准的X.509规范的DER格式封装在参数key中，具体请参考[公钥材料格式](huks-concepts.md#公钥材料格式)。
30
31```c++
32#include "huks/native_huks_api.h"
33#include "huks/native_huks_param.h"
34#include "napi/native_api.h"
35#include <cstring>
36
37/* 以下以生成ECC密钥为例 */
38OH_Huks_Result InitParamSet(struct OH_Huks_ParamSet **paramSet, const struct OH_Huks_Param *params,
39                            uint32_t paramCount)
40{
41    OH_Huks_Result ret = OH_Huks_InitParamSet(paramSet);
42    if (ret.errorCode != OH_HUKS_SUCCESS) {
43        return ret;
44    }
45    ret = OH_Huks_AddParams(*paramSet, params, paramCount);
46    if (ret.errorCode != OH_HUKS_SUCCESS) {
47        OH_Huks_FreeParamSet(paramSet);
48        return ret;
49    }
50    ret = OH_Huks_BuildParamSet(paramSet);
51    if (ret.errorCode != OH_HUKS_SUCCESS) {
52        OH_Huks_FreeParamSet(paramSet);
53        return ret;
54    }
55    return ret;
56}
57
58struct OH_Huks_Param g_testGenerateKeyParam[] = {{.tag = OH_HUKS_TAG_ALGORITHM, .uint32Param = OH_HUKS_ALG_ECC},
59                                                 {.tag = OH_HUKS_TAG_PURPOSE, .uint32Param = OH_HUKS_KEY_PURPOSE_AGREE},
60                                                 {.tag = OH_HUKS_TAG_KEY_SIZE, .uint32Param = OH_HUKS_ECC_KEY_SIZE_256},
61                                                 {.tag = OH_HUKS_TAG_DIGEST, .uint32Param = OH_HUKS_DIGEST_NONE}};
62
63static OH_Huks_Result GenerateKeyHelper(const char *alias)
64{
65    struct OH_Huks_Blob aliasBlob = {.size = (uint32_t)strlen(alias), .data = (uint8_t *)alias};
66    struct OH_Huks_ParamSet *testGenerateKeyParamSet = nullptr;
67    struct OH_Huks_Result ohResult;
68    do {
69        /* 1.初始化密钥属性集 */
70        ohResult = InitParamSet(&testGenerateKeyParamSet, g_testGenerateKeyParam,
71                                sizeof(g_testGenerateKeyParam) / sizeof(OH_Huks_Param));
72        if (ohResult.errorCode != OH_HUKS_SUCCESS) {
73            break;
74        }
75        /* 2.生成密钥 */
76        ohResult = OH_Huks_GenerateKeyItem(&aliasBlob, testGenerateKeyParamSet, nullptr);
77    } while (0);
78    OH_Huks_FreeParamSet(&testGenerateKeyParamSet);
79    return ohResult;
80}
81
82static napi_value ExportKey(napi_env env, napi_callback_info info)
83{
84    /* 1. 参数构造：确定密钥别名 */
85    const char *alias = "test_key";
86    struct OH_Huks_Blob aliasBlob = { .size = (uint32_t)strlen(alias), .data = (uint8_t *)alias };
87
88    /* 生成密钥 */
89    OH_Huks_Result genResult = GenerateKeyHelper(alias);
90    if (genResult.errorCode != OH_HUKS_SUCCESS) {
91        napi_value ret;
92        napi_create_int32(env, genResult.errorCode, &ret);
93        return ret;
94    }
95
96    /* 构造参数：为待导出公钥申请内存 */
97    uint8_t *pubKey = (uint8_t *)malloc(512); // 请业务按实际密钥大小评估申请
98    if (pubKey == nullptr) {
99        return nullptr;
100    }
101    struct OH_Huks_Blob keyBlob = { 256, pubKey };
102    struct OH_Huks_Result ohResult;
103    do {
104        ohResult = OH_Huks_ExportPublicKeyItem(&aliasBlob, nullptr, &keyBlob);
105        if (ohResult.errorCode != OH_HUKS_SUCCESS) {
106            break;
107        }
108    } while (0);
109    free(pubKey);
110    napi_value ret;
111    napi_create_int32(env, ohResult.errorCode, &ret);
112    return ret;
113}
114```
115