harmony 鸿蒙Randomly Generating a Symmetric Key (C/C++)

2025-06-12
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Randomly Generating a Symmetric Key (C/C++)

The following uses AES and SM4 as an example to describe how to randomly generate a symmetric key (OH_CryptoSymKey).

The symmetric key (OH_CryptoSymKey) object created can be used for subsequent encryption and decryption operations, and the binary data can be used for key storage or transfer.

Adding the Dynamic Library in the CMake Script

target_link_libraries(entry PUBLIC libohcrypto.so)

Randomly Generating an AES Key

For details about the algorithm specifications, see AES.

Call OH_CryptoSymKeyGenerator_Create with the string parameter ‘AES256’ to create a symmetric key generator (OH_CryptoSymKeyGenerator) object for a 256-bit AES key.
Call OH_CryptoSymKeyGenerator_Generate to randomly generate a symmetric key object (OH_CryptoSymKey).
Call OH_CryptoSymKey_GetKeyData to obtain the binary data of the key object.

#include "CryptoArchitectureKit/crypto_common.h"
#include "CryptoArchitectureKit/crypto_sym_key.h"

static OH_Crypto_ErrCode testGenerateSymKey()
{
    OH_CryptoSymKeyGenerator *ctx = nullptr;
    OH_CryptoSymKey *keyCtx = nullptr;
    Crypto_DataBlob out = {.data = nullptr, .len = 0};
    OH_Crypto_ErrCode ret = OH_CryptoSymKeyGenerator_Create("AES256", &ctx);
    if (ret != CRYPTO_SUCCESS) {
        return ret;
    }
    ret = OH_CryptoSymKeyGenerator_Generate(ctx, &keyCtx);
    if (ret != CRYPTO_SUCCESS) {
        OH_CryptoSymKeyGenerator_Destroy(ctx);
        return ret;
    }
    ret = OH_CryptoSymKey_GetKeyData(keyCtx, &out);
    OH_CryptoSymKeyGenerator_Destroy(ctx);
    OH_CryptoSymKey_Destroy(keyCtx);
    if (ret != CRYPTO_SUCCESS) {
        return ret;
    }
    OH_Crypto_FreeDataBlob(&out);
    return ret;
}

Randomly Generating an SM4 Key

For details about the algorithm specifications, see SM4.

Call OH_CryptoSymKeyGenerator_Create with the string parameter ‘SM4_128’ to create a symmetric key generator (OH_CryptoSymKeyGenerator) object for a 128-bit SM4 key.
Call OH_CryptoSymKeyGenerator_Generate to randomly generate a symmetric key object (OH_CryptoSymKey).
Call OH_CryptoSymKey_GetKeyData to obtain the binary data of the key object.

#include "CryptoArchitectureKit/crypto_common.h"
#include "CryptoArchitectureKit/crypto_sym_key.h"

static OH_Crypto_ErrCode testGenerateSM4Key()
{
    OH_CryptoSymKeyGenerator *ctx = nullptr;
    OH_CryptoSymKey *keyCtx = nullptr;
    Crypto_DataBlob out = {.data = nullptr, .len = 0}; // Binary data of the symmetric key.
    OH_Crypto_ErrCode ret = OH_CryptoSymKeyGenerator_Create("SM4_128", &ctx); // Create a symmetric key generator.
    if (ret != CRYPTO_SUCCESS) {
        return ret;
    }
    ret = OH_CryptoSymKeyGenerator_Generate(ctx, &keyCtx); // Randomly generate a symmetric key object.
    if (ret != CRYPTO_SUCCESS) {
        OH_CryptoSymKeyGenerator_Destroy(ctx);
        return ret;
    }
    ret = OH_CryptoSymKey_GetKeyData(keyCtx, &out); // Obtain the binary data of the symmetric key object.
    OH_CryptoSymKeyGenerator_Destroy(ctx);
    OH_CryptoSymKey_Destroy(keyCtx);
    if (ret != CRYPTO_SUCCESS) {
        return ret;
    }
    OH_Crypto_FreeDataBlob(&out);
    return ret;
}