xref: /docs/en/application-dev/security/CryptoArchitectureKit/crypto-generate-sym-key-randomly-ndk.md (revision e41f4b71)

# 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 object can be used for subsequent encryption and decryption.

## Adding the Dynamic Library in the CMake Script
```txt
   target_link_libraries(entry PUBLIC libohcrypto.so)
```

## Randomly Generating an AES Key

For details about the algorithm specifications, see [AES](crypto-sym-key-generation-conversion-spec.md#aes).

1. Use [OH_CryptoSymKeyGenerator_Create](../../reference/apis-crypto-architecture-kit/_crypto_sym_key_api.md#oh_cryptosymkeygenerator_create) with the string parameter **'AES256'** to create a symmetric key generator (**OH_CryptoSymKeyGenerator**) object for a 256-bit AES key.
2. Use [OH_CryptoSymKeyGenerator_Generate](../../reference/apis-crypto-architecture-kit/_crypto_sym_key_api.md#oh_cryptosymkeygenerator_generate) to randomly generate a symmetric key object (**OH_CryptoSymKey**).
3. Use [OH_CryptoSymKey_GetKeyData](../../reference/apis-crypto-architecture-kit/_crypto_sym_key_api.md#oh_cryptosymkey_getkeydata) to obtain the binary data of the key object.

**Example**


```c++
#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](crypto-sym-key-generation-conversion-spec.md#sm4).

1. Use [OH_CryptoSymKeyGenerator_Create](../../reference/apis-crypto-architecture-kit/_crypto_sym_key_api.md#oh_cryptosymkeygenerator_create) with the string parameter **'SM4_128'** to create a symmetric key generator (**OH_CryptoSymKeyGenerator**) object for a 128-bit SM4 key.
2. Use [OH_CryptoSymKeyGenerator_Generate](../../reference/apis-crypto-architecture-kit/_crypto_sym_key_api.md#oh_cryptosymkeygenerator_generate) to randomly generate a symmetric key object (**OH_CryptoSymKey**).
3. Use [OH_CryptoSymKey_GetKeyData](../../reference/apis-crypto-architecture-kit/_crypto_sym_key_api.md#oh_cryptosymkey_getkeydata) to obtain the binary data of the key object.

**Example**


```c++
#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};
    OH_Crypto_ErrCode ret = OH_CryptoSymKeyGenerator_Create("SM4_128", &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;
}
```