1# Converting a PEM String into an Asymmetric Key Pair (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 10This topic walks you through on how to convert a string in PEM format into an RSA asymmetric key pair (**OH_CryptoKeyPair**). 11 12> **NOTE** 13> 14> The **convertPemKey** operation must comply with the following requirements: 15> 16> - The public key must comply with X.509 specifications, PKCS\#1 specifications, and PEM encoding format. 17> 18> - The private key must comply with the PKCS\#8, PKCS\#1 specifications, and the PEM encoding format. 19> 20> - Currently, only RSA asymmetric keys can be converted. 21 22## Adding the Dynamic Library in the CMake Script 23```txt 24target_link_libraries(entry PUBLIC libohcrypto.so) 25``` 26 27## Converting a String in PEM Format into an RSA Key Pair 28 29For details about the algorithm specifications, see [RSA](crypto-asym-key-generation-conversion-spec.md#rsa). 30 311. Call [OH_CryptoAsymKeyGenerator_Create](../../reference/apis-crypto-architecture-kit/capi-crypto-asym-key-h.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. 32 33 The default number of primes for creating an RSA asymmetric key is **2**. The **PRIMES_2** parameter is omitted in the string parameter here. 34 352. Call [OH_CryptoAsymKeyGenerator_Convert](../../reference/apis-crypto-architecture-kit/capi-crypto-asym-key-h.md#oh_cryptoasymkeygenerator_convert) to convert the binary data into an asymmetric key pair (**OH_CryptoKeyPair**). 363. Call [OH_CryptoPubKey_Encode](../../reference/apis-crypto-architecture-kit/capi-crypto-asym-key-h.md#oh_cryptopubkey_encode) to convert the public key in the asymmetric key object into the PKCS #1 or X.509 format. 37 38- Example: Convert binary data into an RSA key pair. 39 40```c++ 41#include "CryptoArchitectureKit/crypto_common.h" 42#include "CryptoArchitectureKit/crypto_asym_key.h" 43 44static OH_Crypto_ErrCode doTestPemDataCovertAsymKey() 45{ 46 OH_CryptoAsymKeyGenerator *ctx = nullptr; 47 OH_Crypto_ErrCode ret; 48 49 ret = OH_CryptoAsymKeyGenerator_Create("RSA1024", &ctx); 50 if (ret != CRYPTO_SUCCESS) { 51 return ret; 52 } 53 54 uint8_t pubKeyBlobData[] = { 48,129,159,48,13,6,9,42,134,72,134,247,13,1,1,1,5,0,3,129, 55 141,0,48,129,137,2,129,129,0,235,184,151,247,130,216,140,187,64,124,219,137,140,184,53, 56 137,216,105,156,141,137,165,30,80,232,55,96,46,23,237,197,123,121,27,240,190,14,111,237, 57 172,67,42,47,164,226,248,211,157,213,194,131,109,181,41,173,217,127,252,121,126,26,130, 58 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, 59 220,189,148,13,176,5,139,156,230,143,16,152,79,36,8,112,40,174,35,83,82,57,137,87,123, 60 215,99,199,66,131,150,31,143,56,252,2,73,41,70,159,2,3,1,0,1 }; 61 62 OH_CryptoKeyPair *dupKeyPair = nullptr; 63 Crypto_DataBlob pubBlob = { .data = pubKeyBlobData, .len = sizeof(pubKeyBlobData) }; 64 ret = OH_CryptoAsymKeyGenerator_Convert(ctx, CRYPTO_DER, &pubBlob, nullptr, &dupKeyPair); 65 if (ret != CRYPTO_SUCCESS) { 66 OH_CryptoAsymKeyGenerator_Destroy(ctx); 67 return ret; 68 } 69 70 OH_CryptoPubKey *pubKey1 = OH_CryptoKeyPair_GetPubKey(dupKeyPair); 71 Crypto_DataBlob retBlob = { .data = nullptr, .len = 0 }; 72 ret = OH_CryptoPubKey_Encode(pubKey1, CRYPTO_PEM, "PKCS1", &retBlob); 73 if (ret != CRYPTO_SUCCESS) { 74 OH_CryptoAsymKeyGenerator_Destroy(ctx); 75 OH_CryptoKeyPair_Destroy(dupKeyPair); 76 return ret; 77 } 78 OH_Crypto_FreeDataBlob(&retBlob); 79 OH_CryptoAsymKeyGenerator_Destroy(ctx); 80 OH_CryptoKeyPair_Destroy(dupKeyPair); 81 return ret; 82} 83``` 84