• Home
  • Line#
  • Scopes#
  • Navigate#
  • Raw
  • Download
1# Encryption and Decryption with an SM4 Symmetric Key (CBC Mode) (C/C++)
2
3
4For details about the algorithm specifications, see [SM4](crypto-sym-encrypt-decrypt-spec.md#sm4).
5
6## Adding the Dynamic Library in the CMake Script
7```txt
8target_link_libraries(entry PUBLIC libohcrypto.so)
9```
10
11**Encryption**
12
13
141. Call [OH_CryptoSymKeyGenerator_Create](../../reference/apis-crypto-architecture-kit/_crypto_sym_key_api.md#oh_cryptosymkeygenerator_create) and [OH_CryptoSymKeyGenerator_Generate](../../reference/apis-crypto-architecture-kit/_crypto_sym_key_api.md#oh_cryptosymkeygenerator_generate) to generate a 128-bit SM4 symmetric key (**OH_CryptoSymKey**).
15
16   In addition to the example in this topic, [SM4](crypto-sym-key-generation-conversion-spec.md#sm4) and [Randomly Generating a Symmetric Key](crypto-generate-sym-key-randomly-ndk.md) may help you better understand how to generate an SM4 symmetric key. Note that the input parameters in the reference documents may be different from those in the example below.
17
182. Call [OH_CryptoSymCipher_Create](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_create) with the string parameter **'SM4_128|CBC|PKCS7'** to create a **Cipher** instance for encryption. The key type is **SM4_128**, block cipher mode is **CBC**, and the padding mode is **PKCS7**.
19
203. Call [OH_CryptoSymCipherParams_Create](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipherparams_create) to create a symmetric cipher parameter instance, and call [OH_CryptoSymCipherParams_SetParam](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipherparams_setparam) to set cipher parameters.
21
224. Call [OH_CryptoSymCipher_Init](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_init) to initialize the **Cipher** instance. Specifically, set **mode** to **CRYPTO_ENCRYPT_MODE**, and specify the key for encryption (**OH_CryptoSymKey**) and the encryption parameter instance (**OH_CryptoSymCipherParams**) corresponding to the CBC mode.
23
245. Call [OH_CryptoSymCipher_Update](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_update) to update the data (plaintext) to be encrypted.
25
26   - If a small amount of data is to be encrypted, you can use **OH_CryptoSymCipher_Final()** immediately after **OH_CryptoSymCipher_Init()**.
27   - If a large amount of data is to be encrypted, you can call **OH_CryptoSymCipher_Update()** multiple times to pass in the data by segment.
28
296. Call [OH_CryptoSymCipher_Final](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_final) to generate the ciphertext.
30
31   - If data has been passed in by **OH_CryptoSymCipher_Update()**, pass in **null** in the **data** parameter of **OH_CryptoSymCipher_Final**.
32   - The output of **OH_CryptoSymCipher_Final** may be **null**. To avoid exceptions, always check whether the result is **null** before accessing specific data.
33
347. Call [OH_CryptoSymKeyGenerator_Destroy](../../reference/apis-crypto-architecture-kit/_crypto_sym_key_api.md#oh_cryptosymkeygenerator_destroy), [OH_CryptoSymCipher_Destroy](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_destroy), and [OH_CryptoSymCipherParams_Destroy](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipherparams_destroy) to destroy the instances created.
35
36
37**Decryption**
38
391. Call [OH_CryptoSymCipher_Create](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_create) with the string parameter **'SM4_128|CBC|PKCS7'** to create a **Cipher** instance for decryption. The key type is **SM4_128**, block cipher mode is **CBC**, and the padding mode is **PKCS7**.
40
412. Call [OH_CryptoSymCipher_Init](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_init) initializes the **Cipher** instance. Specifically, set **mode** to **CRYPTO_DECRYPT_MODE**, and specify the key for decryption (**OH_CryptoSymKey**) and the decryption parameter instance (**OH_CryptoSymCipherParams**) corresponding to the CBC mode.
42
433. Call [OH_CryptoSymCipher_Update](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_update) to update the data (ciphertext) to be decrypted.
44
454. Call [OH_CryptoSymCipher_Final](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_final) to generate the plaintext.
46
47**Example**
48
49```c++
50#include "CryptoArchitectureKit/crypto_common.h"
51#include "CryptoArchitectureKit/crypto_sym_cipher.h"
52#include <string.h>
53
54static OH_Crypto_ErrCode doTestSm4Cbc()
55{
56    OH_CryptoSymKeyGenerator *genCtx = nullptr;
57    OH_CryptoSymCipher *encCtx = nullptr;
58    OH_CryptoSymCipher *decCtx = nullptr;
59    OH_CryptoSymKey *keyCtx = nullptr;
60    OH_CryptoSymCipherParams *params = nullptr;
61    Crypto_DataBlob outUpdate = {.data = nullptr, .len = 0};
62    Crypto_DataBlob decUpdate = {.data = nullptr, .len = 0};
63
64    char *plainText = const_cast<char *>("this is test!");
65    Crypto_DataBlob msgBlob = {.data = (uint8_t *)(plainText), .len = strlen(plainText)};
66    uint8_t iv[16] = {1, 2, 4, 12, 3, 4, 2, 3, 3, 2, 0, 4, 3, 1, 0, 10}; // iv is generated from an array of secure random numbers.
67    Crypto_DataBlob ivBlob = {.data = iv, .len = sizeof(iv)};
68    // Generate a symmetric key.
69    OH_Crypto_ErrCode ret;
70    ret = OH_CryptoSymKeyGenerator_Create("SM4_128", &genCtx);
71    if (ret != CRYPTO_SUCCESS) {
72        goto end;
73    }
74    ret = OH_CryptoSymKeyGenerator_Generate(genCtx, &keyCtx);
75    if (ret != CRYPTO_SUCCESS) {
76        goto end;
77    }
78
79    // Set parameters.
80    ret = OH_CryptoSymCipherParams_Create(&params);
81    if (ret != CRYPTO_SUCCESS) {
82        goto end;
83    }
84    ret = OH_CryptoSymCipherParams_SetParam(params, CRYPTO_IV_DATABLOB, &ivBlob);
85    if (ret != CRYPTO_SUCCESS) {
86        goto end;
87    }
88
89    // Encrypt data.
90    ret = OH_CryptoSymCipher_Create("SM4_128|CBC|PKCS7", &encCtx);
91    if (ret != CRYPTO_SUCCESS) {
92        goto end;
93    }
94    ret = OH_CryptoSymCipher_Init(encCtx, CRYPTO_ENCRYPT_MODE, keyCtx, params);
95    if (ret != CRYPTO_SUCCESS) {
96        goto end;
97    }
98    ret = OH_CryptoSymCipher_Final(encCtx, &msgBlob, &outUpdate);
99    if (ret != CRYPTO_SUCCESS) {
100        goto end;
101    }
102
103    // Decrypt data.
104    ret = OH_CryptoSymCipher_Create("SM4_128|CBC|PKCS7", &decCtx);
105    if (ret != CRYPTO_SUCCESS) {
106        goto end;
107    }
108    ret = OH_CryptoSymCipher_Init(decCtx, CRYPTO_DECRYPT_MODE, keyCtx, params);
109    if (ret != CRYPTO_SUCCESS) {
110        goto end;
111    }
112    ret = OH_CryptoSymCipher_Final(decCtx, &outUpdate, &decUpdate);
113    if (ret != CRYPTO_SUCCESS) {
114        goto end;
115    }
116
117    // Release resources.
118end:
119    OH_CryptoSymCipherParams_Destroy(params);
120    OH_CryptoSymCipher_Destroy(encCtx);
121    OH_CryptoSymCipher_Destroy(decCtx);
122    OH_CryptoSymKeyGenerator_Destroy(genCtx);
123    OH_CryptoSymKey_Destroy(keyCtx);
124    OH_Crypto_FreeDataBlob(&outUpdate);
125    OH_Crypto_FreeDataBlob(&decUpdate);
126    return ret;
127}
128```
129