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1# 使用SM2密文格式转换(C/C++)
2
3<!--Kit: Crypto Architecture Kit-->
4<!--Subsystem: Security-->
5<!--Owner: @zxz--3-->
6<!--Designer: @lanming-->
7<!--Tester: @PAFT-->
8<!--Adviser: @zengyawen-->
9
10当前支持的SM2密文格式为国密标准的ASN.1格式，其中各参数组合顺序为C1C3C2，具体参数含义请参考[转换SM2密文格式](crypto-asym-encrypt-decrypt-spec.md#转换sm2密文格式)。
11
12开发者可指定SM2密文的参数，将其转换成符合国密标准的ASN.1格式密文。反之，也可以从国密标准的ASN.1格式密文中取出具体的SM2密文参数，便于开发者自行组合成其他格式的SM2密文。
13
14**指定密文参数，生成标准ASN.1密文**
15
161. 调用[OH_CryptoSm2CiphertextSpec_Create](../../reference/apis-crypto-architecture-kit/capi-crypto-asym-cipher-h.md#oh_cryptosm2ciphertextspec_create)，创建空的SM2密文规格对象。
17
182. 调用[OH_CryptoSm2CiphertextSpec_SetItem](../../reference/apis-crypto-architecture-kit/capi-crypto-asym-cipher-h.md#oh_cryptosm2ciphertextspec_setitem)，设置密文的各个参数（C1.x、C1.y、C2、C3）。
19
203. 调用[OH_CryptoSm2CiphertextSpec_Encode](../../reference/apis-crypto-architecture-kit/capi-crypto-asym-cipher-h.md#oh_cryptosm2ciphertextspec_encode)，生成ASN.1格式的密文（当前密文转换仅支持SM3，实现中只校验hash长度是否为32字节）。
21
224. 使用完毕后，调用[OH_CryptoSm2CiphertextSpec_Destroy](../../reference/apis-crypto-architecture-kit/capi-crypto-asym-cipher-h.md#oh_cryptosm2ciphertextspec_destroy)销毁SM2密文规格对象。
23
24```C++
25#include "CryptoArchitectureKit/crypto_architecture_kit.h"
26
27static OH_Crypto_ErrCode doTestGenCipherTextBySpec()
28{
29    // 准备SM2密文参数。
30    uint8_t c1x[] = {45, 153, 88, 82, 104, 221, 226, 43, 174, 21, 122, 248, 5, 232, 105, 41, 92, 95, 102, 224,
31                     216, 149, 85, 236, 110, 6, 64, 188, 149, 70, 70, 183};
32    uint8_t c1y[] = {107, 93, 198, 247, 119, 18, 40, 110, 90, 156, 193, 158, 205, 113, 170, 128, 146, 109, 75,
33                     17, 181, 109, 110, 91, 149, 5, 110, 233, 209, 78, 229, 96};
34    uint8_t c2[] = {100, 227, 78, 195, 249, 179, 43, 70, 242, 69, 169, 10, 65, 123};
35    uint8_t c3[] = {87, 167, 167, 247, 88, 146, 203, 234, 83, 126, 117, 129, 52, 142, 82, 54, 152, 226, 201, 111,
36                    143, 115, 169, 125, 128, 42, 157, 31, 114, 198, 109, 244};
37
38    // 创建空的SM2密文规格对象。
39    OH_CryptoSm2CiphertextSpec *sm2CipherSpec = nullptr;
40    OH_Crypto_ErrCode ret = OH_CryptoSm2CiphertextSpec_Create(nullptr, &sm2CipherSpec);
41    if (ret != CRYPTO_SUCCESS) {
42        return ret;
43    }
44
45    // 设置各个参数。
46    Crypto_DataBlob c1xBlob = {c1x, sizeof(c1x)};
47    Crypto_DataBlob c1yBlob = {c1y, sizeof(c1y)};
48    Crypto_DataBlob c2Blob = {c2, sizeof(c2)};
49    Crypto_DataBlob c3Blob = {c3, sizeof(c3)};
50
51    ret = OH_CryptoSm2CiphertextSpec_SetItem(sm2CipherSpec, CRYPTO_SM2_CIPHERTEXT_C1_X, &c1xBlob);
52    if (ret != CRYPTO_SUCCESS) {
53        OH_CryptoSm2CiphertextSpec_Destroy(sm2CipherSpec);
54        return ret;
55    }
56    ret = OH_CryptoSm2CiphertextSpec_SetItem(sm2CipherSpec, CRYPTO_SM2_CIPHERTEXT_C1_Y, &c1yBlob);
57    if (ret != CRYPTO_SUCCESS) {
58        OH_CryptoSm2CiphertextSpec_Destroy(sm2CipherSpec);
59        return ret;
60    }
61    ret = OH_CryptoSm2CiphertextSpec_SetItem(sm2CipherSpec, CRYPTO_SM2_CIPHERTEXT_C2, &c2Blob);
62    if (ret != CRYPTO_SUCCESS) {
63        OH_CryptoSm2CiphertextSpec_Destroy(sm2CipherSpec);
64        return ret;
65    }
66    ret = OH_CryptoSm2CiphertextSpec_SetItem(sm2CipherSpec, CRYPTO_SM2_CIPHERTEXT_C3, &c3Blob);
67    if (ret != CRYPTO_SUCCESS) {
68        OH_CryptoSm2CiphertextSpec_Destroy(sm2CipherSpec);
69        return ret;
70    }
71
72    // 编码为ASN.1格式。
73    Crypto_DataBlob encoded = { 0 };
74    ret = OH_CryptoSm2CiphertextSpec_Encode(sm2CipherSpec, &encoded);
75    if (ret != CRYPTO_SUCCESS) {
76        OH_CryptoSm2CiphertextSpec_Destroy(sm2CipherSpec);
77        return ret;
78    }
79
80    // 清理资源。
81    OH_Crypto_FreeDataBlob(&encoded);
82    OH_CryptoSm2CiphertextSpec_Destroy(sm2CipherSpec);
83    return ret;
84}
85```
86
87**从标准ASN.1密文中获取密文参数**
88
891. 调用[OH_CryptoSm2CiphertextSpec_Create](../../reference/apis-crypto-architecture-kit/capi-crypto-asym-cipher-h.md#oh_cryptosm2ciphertextspec_create)，从ASN.1格式密文创建SM2密文规格对象。
90
912. 调用[OH_CryptoSm2CiphertextSpec_GetItem](../../reference/apis-crypto-architecture-kit/capi-crypto-asym-cipher-h.md#oh_cryptosm2ciphertextspec_getitem)，获取密文中的各个参数（C1.x、C1.y、C2、C3）。
92
933. 使用完毕后，调用[OH_CryptoSm2CiphertextSpec_Destroy](../../reference/apis-crypto-architecture-kit/capi-crypto-asym-cipher-h.md#oh_cryptosm2ciphertextspec_destroy)销毁SM2密文规格对象。
94
95```C++
96include "CryptoArchitectureKit/crypto_architecture_kit.h"
97
98static OH_Crypto_ErrCode doTestGetCipherTextSpec()
99{
100    // 准备标准ASN.1格式密文。
101    uint8_t cipherTextArray[] = {48, 118, 2, 32, 45, 153, 88, 82, 104, 221, 226, 43, 174, 21, 122, 248, 5, 232, 105,
102                                41, 92, 95, 102, 224, 216, 149, 85, 236, 110, 6, 64, 188, 149, 70, 70, 183, 2, 32, 107,
103                                93, 198, 247, 119, 18, 40, 110, 90, 156, 193, 158, 205, 113, 170, 128, 146, 109, 75, 17,
104                                181, 109, 110, 91, 149, 5, 110, 233, 209, 78, 229, 96, 4, 32, 87, 167, 167, 247, 88, 146,
105                                203, 234, 83, 126, 117, 129, 52, 142, 82, 54, 152, 226, 201, 111, 143, 115, 169, 125, 128,
106                                42, 157, 31, 114, 198, 109, 244, 4, 14, 100, 227, 78, 195, 249, 179, 43, 70, 242, 69, 169,
107                                10, 65, 123};
108    Crypto_DataBlob cipherText = {cipherTextArray, sizeof(cipherTextArray)};
109
110    // 从ASN.1格式密文创建SM2密文规格对象。
111    OH_CryptoSm2CiphertextSpec *sm2CipherSpec = nullptr;
112    OH_Crypto_ErrCode ret = OH_CryptoSm2CiphertextSpec_Create(&cipherText, &sm2CipherSpec);
113    if (ret != CRYPTO_SUCCESS) {
114        return ret;
115    }
116
117    // 获取各个参数。
118    Crypto_DataBlob c1x = { 0 };
119    Crypto_DataBlob c1y = { 0 };
120    Crypto_DataBlob c2 = { 0 };
121    Crypto_DataBlob c3 = { 0 };
122
123    ret = OH_CryptoSm2CiphertextSpec_GetItem(sm2CipherSpec, CRYPTO_SM2_CIPHERTEXT_C1_X, &c1x);
124    if (ret != CRYPTO_SUCCESS) {
125        goto EXIT;
126    }
127    ret = OH_CryptoSm2CiphertextSpec_GetItem(sm2CipherSpec, CRYPTO_SM2_CIPHERTEXT_C1_Y, &c1y);
128    if (ret != CRYPTO_SUCCESS) {
129        goto EXIT;
130    }
131    ret = OH_CryptoSm2CiphertextSpec_GetItem(sm2CipherSpec, CRYPTO_SM2_CIPHERTEXT_C2, &c2);
132    if (ret != CRYPTO_SUCCESS) {
133        goto EXIT;
134    }
135    ret = OH_CryptoSm2CiphertextSpec_GetItem(sm2CipherSpec, CRYPTO_SM2_CIPHERTEXT_C3, &c3);
136    if (ret != CRYPTO_SUCCESS) {
137        goto EXIT;
138    }
139
140EXIT:
141    OH_Crypto_FreeDataBlob(&c1x);
142    OH_Crypto_FreeDataBlob(&c1y);
143    OH_Crypto_FreeDataBlob(&c2);
144    OH_Crypto_FreeDataBlob(&c3);
145    OH_CryptoSm2CiphertextSpec_Destroy(sm2CipherSpec);
146    return ret;
147}
148```
149