1# Encryption and Decryption with an AES Symmetric Key (CBC Mode) (C/C++)
2
3
4For details about the algorithm specifications, see [AES](crypto-sym-encrypt-decrypt-spec.md#aes).
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6
7## Adding the Dynamic Library in the CMake Script
8```txt
9   target_link_libraries(entry PUBLIC libohcrypto.so)
10```
11
12## How to Develop
13
14
15**Encryption**
16
171. Use [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 AES symmetric key (**OH_CryptoSymKey**).
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19   In addition to the example in this topic, [AES](crypto-sym-key-generation-conversion-spec.md#aes) and [Randomly Generating a Symmetric Key](crypto-generate-sym-key-randomly-ndk.md) may help you better understand how to generate an AES symmetric key. Note that the input parameters in the reference documents may be different from those in the example below.
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212. Use [OH_CryptoSymCipher_Create](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_create) with the string parameter **'AES128|CBC|PKCS7'** to create a **Cipher** instance. The key type is **AES128**, block cipher mode is **CBC**, and the padding mode is **PKCS7**.
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233. Use [OH_CryptoSymCipherParams_Create](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipherparams_create) to create a symmetric cipher parameter instance, and use [OH_CryptoSymCipherParams_SetParam](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipherparams_setparam) to set cipher parameters.
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254. Use [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.
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275. If a small amount of data is to be encrypted, use [OH_CryptoSymCipher_Final](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_final) to generate the encrypted data. If a large amount of data is to be encrypted, you can call [OH_CryptoSymCipher_Update](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_update) multiple times to pass in the data by segment, and then use **OH_CryptoSymCipher_Final** to generate the ciphertext.
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296. Use [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.
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31
32**Decryption**
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34
351. Use [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_DECRYPT_MODE**, and specify the key for decryption (**OH_CryptoSymKey**) and the decryption parameter instance (**OH_CryptoSymCipherParams**) corresponding to the CBC mode.
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372. If a small amount of data is to be decrypted, use [OH_CryptoSymCipher_Final](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_final) to generate the decrypted data. If a large amount of data is to be decrypted, you can call [OH_CryptoSymCipher_Update](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipher_update) multiple times to pass in the data by segment, and then use **OH_CryptoSymCipher_Final** to generate the plaintext.
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39
40
41```c++
42#include "CryptoArchitectureKit/crypto_common.h"
43#include "CryptoArchitectureKit/crypto_sym_cipher.h"
44#include <string.h>
45
46static OH_Crypto_ErrCode doTestAesCbc()
47{
48    OH_CryptoSymKeyGenerator *genCtx = nullptr;
49    OH_CryptoSymCipher *encCtx = nullptr;
50    OH_CryptoSymCipher *decCtx = nullptr;
51    OH_CryptoSymKey *keyCtx = nullptr;
52    OH_CryptoSymCipherParams *params = nullptr;
53    Crypto_DataBlob outUpdate = {.data = nullptr, .len = 0};
54    Crypto_DataBlob decUpdate = {.data = nullptr, .len = 0};
55    char *plainText = const_cast<char *>("this is test!");
56    Crypto_DataBlob msgBlob = {.data = (uint8_t *)(plainText), .len = strlen(plainText)};
57    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.
58    Crypto_DataBlob ivBlob = {.data = iv, .len = sizeof(iv)};
59    // Generate a symmetric key.
60    OH_Crypto_ErrCode ret;
61    ret = OH_CryptoSymKeyGenerator_Create("AES128", &genCtx);
62    if (ret != CRYPTO_SUCCESS) {
63        goto end;
64    }
65    ret = OH_CryptoSymKeyGenerator_Generate(genCtx, &keyCtx);
66    if (ret != CRYPTO_SUCCESS) {
67        goto end;
68    }
69
70    // Set parameters.
71    ret = OH_CryptoSymCipherParams_Create(&params);
72    if (ret != CRYPTO_SUCCESS) {
73        goto end;
74    }
75    ret = OH_CryptoSymCipherParams_SetParam(params, CRYPTO_IV_DATABLOB, &ivBlob);
76    if (ret != CRYPTO_SUCCESS) {
77        goto end;
78    }
79
80    // Encrypt data.
81    ret = OH_CryptoSymCipher_Create("AES128|CBC|PKCS7", &encCtx);
82    if (ret != CRYPTO_SUCCESS) {
83        goto end;
84    }
85    ret = OH_CryptoSymCipher_Init(encCtx, CRYPTO_ENCRYPT_MODE, keyCtx, params);
86    if (ret != CRYPTO_SUCCESS) {
87        goto end;
88    }
89    ret = OH_CryptoSymCipher_Final(encCtx, &msgBlob, &outUpdate);
90    if (ret != CRYPTO_SUCCESS) {
91        goto end;
92    }
93
94    // Decrypt data.
95    ret = OH_CryptoSymCipher_Create("AES128|CBC|PKCS7", &decCtx);
96    if (ret != CRYPTO_SUCCESS) {
97        goto end;
98    }
99    ret = OH_CryptoSymCipher_Init(decCtx, CRYPTO_DECRYPT_MODE, keyCtx, params);
100    if (ret != CRYPTO_SUCCESS) {
101        goto end;
102    }
103    ret = OH_CryptoSymCipher_Final(decCtx, &outUpdate, &decUpdate);
104    if (ret != CRYPTO_SUCCESS) {
105        goto end;
106    }
107
108end:
109    OH_CryptoSymCipherParams_Destroy(params);
110    OH_CryptoSymCipher_Destroy(encCtx);
111    OH_CryptoSymCipher_Destroy(decCtx);
112    OH_CryptoSymKeyGenerator_Destroy(genCtx);
113    OH_CryptoSymKey_Destroy(keyCtx);
114    OH_Crypto_FreeDataBlob(&outUpdate);
115    OH_Crypto_FreeDataBlob(&decUpdate);
116    return ret;
117}
118```
119