1# 使用AES对称密钥(GCM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:AES](crypto-sym-encrypt-decrypt-spec.md#aes)。
5
6
7## 在CMake脚本中链接相关动态库
8```txt
9   target_link_libraries(entry PUBLIC libohcrypto.so)
10```
11
12## 开发步骤
13
14**加密**
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16
171. 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AES、密钥长度为128位的对称密钥(OH_CryptoSymKey)。
18
19   如何生成AES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:AES](crypto-sym-key-generation-conversion-spec.md#aes)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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212. 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'AES128|GCM|PKCS7',创建对称密钥类型为AES128、分组模式为GCM、填充模式为PKCS7的Cipher实例,用于完成加解密操作。
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233. 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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254. 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GCM模式对应的加密参数(OH_CryptoSymCipherParams),初始化加密Cipher实例。
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275. 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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29   当前单次update长度没有限制,开发者可以根据数据量判断如何调用update。
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31   - 当数据量较小时,可以在init完成后直接调用final。
32   - 当数据量较大时,可以多次调用update,即分段加解密。
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346. 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。
35   - 由于已使用update传入数据,此处data传入null。
36   - 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。
37
387. 使用[OH_CryptoSymCipherParams_Create](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipherparams_create)创建Params,使用[OH_CryptoSymCipherParams_SetParam](../../reference/apis-crypto-architecture-kit/_crypto_sym_cipher_api.md#oh_cryptosymcipherparams_setparam)设置authTag,作为解密的认证信息。
39   在GCM模式下,需要从加密后的数据中取出末尾16字节,作为解密时初始化的认证信息。示例中authTag恰好为16字节。
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418. 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。
42
43
44**解密**
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46
471. 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GCM模式对应的解密参数(OH_CryptoSymCipherParams),初始化解密Cipher实例。
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492. 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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513. 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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53
54- AES GCM模式加解密示例如下:
55
56```c++
57#include "CryptoArchitectureKit/crypto_common.h"
58#include "CryptoArchitectureKit/crypto_sym_cipher.h"
59#include <string.h>
60
61static OH_Crypto_ErrCode doTestAesGcm()
62{
63    OH_CryptoSymKeyGenerator *genCtx = nullptr;
64    OH_CryptoSymCipher *encCtx = nullptr;
65    OH_CryptoSymCipher *decCtx = nullptr;
66    OH_CryptoSymKey *keyCtx = nullptr;
67    OH_CryptoSymCipherParams *params = nullptr;
68
69    Crypto_DataBlob outUpdate = {.data = nullptr, .len = 0};
70    Crypto_DataBlob decUpdate = {.data = nullptr, .len = 0};
71
72    uint8_t aad[8] = {1, 2, 3, 4, 5, 6, 7, 8};
73    uint8_t tag[16] = {0};
74    uint8_t iv[12] = {1, 2, 4, 12, 3, 4, 2, 3, 3, 2, 0, 4}; // iv使用安全随机数生成
75    Crypto_DataBlob ivData = {.data = iv, .len = sizeof(iv)};
76    Crypto_DataBlob aadData = {.data = aad, .len = sizeof(aad)};
77    Crypto_DataBlob tagData = {.data = tag, .len = sizeof(tag)};
78    Crypto_DataBlob tagOutPut = {.data = nullptr, .len = 0};
79    char *plainText = const_cast<char *>("this is test!");
80    Crypto_DataBlob msgBlob = {.data = (uint8_t *)(plainText), .len = strlen(plainText)};
81
82    // 生成对称密钥
83    OH_Crypto_ErrCode ret;
84    ret = OH_CryptoSymKeyGenerator_Create("AES128", &genCtx);
85    if (ret != CRYPTO_SUCCESS) {
86        goto end;
87    }
88    ret = OH_CryptoSymKeyGenerator_Generate(genCtx, &keyCtx);
89    if (ret != CRYPTO_SUCCESS) {
90        goto end;
91    }
92
93    // 设置参数
94    ret = OH_CryptoSymCipherParams_Create(&params);
95    if (ret != CRYPTO_SUCCESS) {
96        goto end;
97    }
98    ret = OH_CryptoSymCipherParams_SetParam(params, CRYPTO_IV_DATABLOB, &ivData);
99    if (ret != CRYPTO_SUCCESS) {
100        goto end;
101    }
102    ret = OH_CryptoSymCipherParams_SetParam(params, CRYPTO_AAD_DATABLOB, &aadData);
103    if (ret != CRYPTO_SUCCESS) {
104        goto end;
105    }
106    ret = OH_CryptoSymCipherParams_SetParam(params, CRYPTO_TAG_DATABLOB, &tagData);
107    if (ret != CRYPTO_SUCCESS) {
108        goto end;
109    }
110
111    // 加密
112    ret = OH_CryptoSymCipher_Create("AES128|GCM|PKCS7", &encCtx);
113    if (ret != CRYPTO_SUCCESS) {
114        goto end;
115    }
116    ret = OH_CryptoSymCipher_Init(encCtx, CRYPTO_ENCRYPT_MODE, keyCtx, params);
117    if (ret != CRYPTO_SUCCESS) {
118        goto end;
119    }
120    ret = OH_CryptoSymCipher_Update(encCtx, &msgBlob, &outUpdate);
121    if (ret != CRYPTO_SUCCESS) {
122        goto end;
123    }
124    ret = OH_CryptoSymCipher_Final(encCtx, nullptr, &tagOutPut);
125    if (ret != CRYPTO_SUCCESS) {
126        goto end;
127    }
128
129    // 解密
130    ret = OH_CryptoSymCipher_Create("AES128|GCM|PKCS7", &decCtx);
131    if (ret != CRYPTO_SUCCESS) {
132        goto end;
133    }
134    ret = OH_CryptoSymCipherParams_SetParam(params, CRYPTO_TAG_DATABLOB, &tagOutPut);
135    if (ret != CRYPTO_SUCCESS) {
136        goto end;
137    }
138    ret = OH_CryptoSymCipher_Init(decCtx, CRYPTO_DECRYPT_MODE, keyCtx, params);
139    if (ret != CRYPTO_SUCCESS) {
140        goto end;
141    }
142    ret = OH_CryptoSymCipher_Final(decCtx, &outUpdate, &decUpdate);
143    if (ret != CRYPTO_SUCCESS) {
144        goto end;
145    }
146
147end:
148    OH_CryptoSymCipherParams_Destroy(params);
149    OH_CryptoSymCipher_Destroy(encCtx);
150    OH_CryptoSymCipher_Destroy(decCtx);
151    OH_CryptoSymKeyGenerator_Destroy(genCtx);
152    OH_CryptoSymKey_Destroy(keyCtx);
153    OH_Crypto_FreeDataBlob(&outUpdate);
154    OH_Crypto_FreeDataBlob(&decUpdate);
155    OH_Crypto_FreeDataBlob(&tagOutPut);
156    return ret;
157}
158```