1# Converting a PEM String into an Asymmetric Key Pair (C/C++)
2
3
4This topic walks you through on how to convert a string in PEM format into an RSA asymmetric key pair (**OH_CryptoKeyPair**).
5
6> **NOTE**
7>
8> The **convertPemKey** operation must comply with the following requirements:
9>
10> - The public key must comply with X.509 specifications, PKCS\#1 specifications, and PEM encoding format.
11>
12> - The private key must comply with the PKCS\#8 or PKCS\#1 specifications and the PEM encoding format.
13>
14> - Currently, only RSA asymmetric keys can be converted.
15
16## Adding the Dynamic Library in the CMake Script
17```txt
18   target_link_libraries(entry PUBLIC libohcrypto.so)
19```
20
21
22## Converting a String in PEM Format into an RSA Key Pair
23
24For details about the algorithm specifications, see [RSA](crypto-asym-key-generation-conversion-spec.md#rsa).
25
261. Use [OH_CryptoAsymKeyGenerator_Create](../../reference/apis-crypto-architecture-kit/_crypto_asym_key_api.md#oh_cryptoasymkeygenerator_create) with the string parameter **'RSA1024'** to create an asymmetric key generator (**OH_CryptoAsymKeyGenerator**) object for a 1024-bit RSA key with two primes.
27
28   The default number of primes for creating an RSA asymmetric key is **2**. The **PRIMES_2** parameter is omitted in the string parameter here.
29
302. Use [OH_CryptoAsymKeyGenerator_Convert](../../reference/apis-crypto-architecture-kit/_crypto_asym_key_api.md#oh_cryptoasymkeygenerator_convert) to convert the binary data into an asymmetric key pair (**OH_CryptoKeyPair**).
313. Use [OH_CryptoPubKey_Encode](../../reference/apis-crypto-architecture-kit/_crypto_asym_key_api.md#oh_cryptopubkey_encode) to convert the public key in the asymmetric key object into PKCS #1 or X.509 format.
32
33Example: Convert binary data into an RSA key pair.
34
35```c++
36#include "CryptoArchitectureKit/crypto_common.h"
37#include "CryptoArchitectureKit/crypto_asym_key.h"
38
39static OH_Crypto_ErrCode doTestPemDataCovertAsymKey()
40{
41   OH_CryptoAsymKeyGenerator *ctx = nullptr;
42   OH_Crypto_ErrCode ret;
43
44   ret = OH_CryptoAsymKeyGenerator_Create("RSA1024", &ctx);
45   if (ret != CRYPTO_SUCCESS) {
46      return ret;
47   }
48
49   uint8_t sm2PubKeyBlobData[] = { 48,129,159,48,13,6,9,42,134,72,134,247,13,1,1,1,5,0,3,129,
50      141,0,48,129,137,2,129,129,0,235,184,151,247,130,216,140,187,64,124,219,137,140,184,53,
51      137,216,105,156,141,137,165,30,80,232,55,96,46,23,237,197,123,121,27,240,190,14,111,237,
52      172,67,42,47,164,226,248,211,157,213,194,131,109,181,41,173,217,127,252,121,126,26,130,
53      55,4,134,104,73,5,132,91,214,146,232,64,99,87,33,222,155,159,9,59,212,144,46,183,83,89,
54      220,189,148,13,176,5,139,156,230,143,16,152,79,36,8,112,40,174,35,83,82,57,137,87,123,
55      215,99,199,66,131,150,31,143,56,252,2,73,41,70,159,2,3,1,0,1 };
56
57   OH_CryptoKeyPair *dupKeyPair = nullptr;
58   Crypto_DataBlob pubBlob = { .data = sm2PubKeyBlobData, .len = sizeof(sm2PubKeyBlobData) };
59   ret = OH_CryptoAsymKeyGenerator_Convert(ctx, CRYPTO_DER, &pubBlob, nullptr, &dupKeyPair);
60   if (ret != CRYPTO_SUCCESS) {
61      OH_CryptoAsymKeyGenerator_Destroy(ctx);
62      return ret;
63   }
64
65   OH_CryptoPubKey *pubKey1 = OH_CryptoKeyPair_GetPubKey(dupKeyPair);
66   Crypto_DataBlob retBlob = { .data = nullptr, .len = 0 };
67   ret = OH_CryptoPubKey_Encode(pubKey1, CRYPTO_PEM, "PKCS1", &retBlob);
68   if (ret != CRYPTO_SUCCESS) {
69      OH_CryptoAsymKeyGenerator_Destroy(ctx);
70      OH_CryptoKeyPair_Destroy(dupKeyPair);
71      return ret;
72   }
73   OH_Crypto_FreeDataBlob(&retBlob);
74   OH_CryptoAsymKeyGenerator_Destroy(ctx);
75   OH_CryptoKeyPair_Destroy(dupKeyPair);
76   return ret;
77}
78```
79