1# 使用SM4对称密钥(CBC模式)加解密(C/C++)
2
3
4对应的算法规格请查看[对称密钥加解密算法规格:SM4](crypto-sym-encrypt-decrypt-spec.md#sm4)。
5
6## 在CMake脚本中链接相关动态库
7```txt
8   target_link_libraries(entry PUBLIC libohcrypto.so)
9```
10
11**加密**
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13
141. 调用[OH_CryptoSymKeyGenerator_Create](../../reference/apis-crypto-architecture-kit/_crypto_sym_key_api.md#oh_cryptosymkeygenerator_create)、[OH_CryptoSymKeyGenerator_Generate](../../reference/apis-crypto-architecture-kit/_crypto_sym_key_api.md#oh_cryptosymkeygenerator_generate),生成密钥算法为SM4、密钥长度为128位的对称密钥(OH_CryptoSymKey)。
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16   如何生成SM4对称密钥,开发者可参考下文示例,并结合[对称密钥生成和转换规格:SM4](crypto-sym-key-generation-conversion-spec.md#sm4)和[随机生成对称密钥](crypto-generate-sym-key-randomly-ndk.md)理解,参考文档与当前示例可能存在入参差异,请在阅读时注意区分。
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182. 调用[OH_CryptoSymCipher_Create](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_create),指定字符串参数'SM4_128|CBC|PKCS7',创建对称密钥类型为SM4_128、分组模式为CBC、填充模式为PKCS7的Cipher实例,用于完成加解密操作。
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203. 调用[OH_CryptoSymCipherParams_Create](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipherparams_create)创建参数对象,调用[OH_CryptoSymCipherParams_SetParam](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipherparams_setparam)设置对应的加密参数。
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224. 调用[OH_CryptoSymCipher_Init](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_init),设置模式为加密(CRYPTO_ENCRYPT_MODE),指定加密密钥(OH_CryptoSymKey)和CBC模式对应的加密参数(OH_CryptoSymCipherParams),初始化加密Cipher实例。
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245. 调用[OH_CryptoSymCipher_Update](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_update),更新数据(明文)。
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26   - 当数据量较小时,可以在init完成后直接调用final。
27   - 当数据量较大时,可以多次调用update,即分段加解密。
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296. 调用[OH_CryptoSymCipher_Final](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_final),获取加密后的数据。
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31   - 由于已使用update传入数据,此处data传入null。
32   - final输出结果可能为null,在访问具体数据前,需要先判断结果是否为null,避免产生异常。
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347. 调用[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)、[OH_CryptoSymCipherParams_Destroy](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipherparams_destroy)销毁各对象。
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36
37**解密**
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401. 调用[OH_CryptoSymCipher_Init](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_init),设置模式为解密(CRYPTO_DECRYPT_MODE),指定解密密钥(OH_CryptoSymKey)和CBC模式对应的解密参数(OH_CryptoSymCipherParams),初始化解密Cipher实例。
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422. 调用[OH_CryptoSymCipher_Update](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_update),更新数据(密文)。
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443. 调用[OH_CryptoSymCipher_Final](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_final),获取解密后的数据。
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46
47
48```c++
49#include "CryptoArchitectureKit/crypto_common.h"
50#include "CryptoArchitectureKit/crypto_sym_cipher.h"
51#include <string.h>
52
53static OH_Crypto_ErrCode doTestSm4Cbc()
54{
55    OH_CryptoSymKeyGenerator *genCtx = nullptr;
56    OH_CryptoSymCipher *encCtx = nullptr;
57    OH_CryptoSymCipher *decCtx = nullptr;
58    OH_CryptoSymKey *keyCtx = nullptr;
59    OH_CryptoSymCipherParams *params = nullptr;
60    Crypto_DataBlob outUpdate = {.data = nullptr, .len = 0};
61    Crypto_DataBlob decUpdate = {.data = nullptr, .len = 0};
62
63    char *plainText = const_cast<char *>("this is test!");
64    Crypto_DataBlob msgBlob = {.data = (uint8_t *)(plainText), .len = strlen(plainText)};
65    uint8_t iv[16] = {1, 2, 4, 12, 3, 4, 2, 3, 3, 2, 0, 4, 3, 1, 0, 10}; // iv使用安全随机数生成
66    Crypto_DataBlob ivBlob = {.data = iv, .len = sizeof(iv)};
67    // 生成对称密钥
68    OH_Crypto_ErrCode ret;
69    ret = OH_CryptoSymKeyGenerator_Create("SM4_128", &genCtx);
70    if (ret != CRYPTO_SUCCESS) {
71        goto end;
72    }
73    ret = OH_CryptoSymKeyGenerator_Generate(genCtx, &keyCtx);
74    if (ret != CRYPTO_SUCCESS) {
75        goto end;
76    }
77
78    // 设置参数
79    ret = OH_CryptoSymCipherParams_Create(&params);
80    if (ret != CRYPTO_SUCCESS) {
81        goto end;
82    }
83    ret = OH_CryptoSymCipherParams_SetParam(params, CRYPTO_IV_DATABLOB, &ivBlob);
84    if (ret != CRYPTO_SUCCESS) {
85        goto end;
86    }
87
88    // 加密
89    ret = OH_CryptoSymCipher_Create("SM4_128|CBC|PKCS7", &encCtx);
90    if (ret != CRYPTO_SUCCESS) {
91        goto end;
92    }
93    ret = OH_CryptoSymCipher_Init(encCtx, CRYPTO_ENCRYPT_MODE, keyCtx, params);
94    if (ret != CRYPTO_SUCCESS) {
95        goto end;
96    }
97    ret = OH_CryptoSymCipher_Final(encCtx, &msgBlob, &outUpdate);
98    if (ret != CRYPTO_SUCCESS) {
99        goto end;
100    }
101
102    // 解密
103    ret = OH_CryptoSymCipher_Create("SM4_128|CBC|PKCS7", &decCtx);
104    if (ret != CRYPTO_SUCCESS) {
105        goto end;
106    }
107    ret = OH_CryptoSymCipher_Init(decCtx, CRYPTO_DECRYPT_MODE, keyCtx, params);
108    if (ret != CRYPTO_SUCCESS) {
109        goto end;
110    }
111    ret = OH_CryptoSymCipher_Final(decCtx, &outUpdate, &decUpdate);
112    if (ret != CRYPTO_SUCCESS) {
113        goto end;
114    }
115
116    // 资源释放
117end:
118    OH_CryptoSymCipherParams_Destroy(params);
119    OH_CryptoSymCipher_Destroy(encCtx);
120    OH_CryptoSymCipher_Destroy(decCtx);
121    OH_CryptoSymKeyGenerator_Destroy(genCtx);
122    OH_CryptoSymKey_Destroy(keyCtx);
123    OH_Crypto_FreeDataBlob(&outUpdate);
124    OH_Crypto_FreeDataBlob(&decUpdate);
125    return ret;
126}
127```