# Signature Recovery Using an RSA Key Pair (PKCS1 Mode) (C/C++)


For details about the algorithm specifications, see [RSA](crypto-sign-sig-verify-overview.md#rsa).


## Adding the Dynamic Library in the CMake Script
```txt
   target_link_libraries(entry PUBLIC libohcrypto.so)
```

## How to Develop


1. Use [OH_CryptoVerify_Create](../../reference/apis-crypto-architecture-kit/_crypto_signature_api.md#oh_cryptoverify_create) with the string parameter **'RSA1024|PKCS1|SHA256|Recover'** to create a **Verify** instance. The key parameters must be the same as that used to create the **Sign** instance.

2. Use [OH_CryptoVerify_Init](../../reference/apis-crypto-architecture-kit/_crypto_signature_api.md#oh_cryptoverify_init) to initialize the **Verify** instance by using the public key (**OH_CryptoPubKey**).

3. Use [OH_CryptoVerify_Recover](../../reference/apis-crypto-architecture-kit/_crypto_signature_api.md#oh_cryptoverify_recover) to restore the data.

**Example**

```c++
#include "CryptoArchitectureKit/crypto_common.h"
#include "CryptoArchitectureKit/crypto_signature.h"
#include "CryptoArchitectureKit/crypto_asym_key.h"

static OH_Crypto_ErrCode doTestRsaSignatureRecover()
{
   OH_CryptoAsymKeyGenerator *keyCtx = nullptr;
   OH_CryptoKeyPair *keyPair = nullptr;
   OH_CryptoVerify *verify = nullptr;

   uint8_t plainText[] = {
      0xc4, 0xa5, 0xe5, 0x45, 0xee, 0x71, 0x5e, 0x3b, 0x24, 0x1d, 0x7e, 0x62, 0xd6, 0x6b, 0xab, 0x98,
      0x88, 0x0f, 0xaf, 0x1e, 0x96, 0xa0, 0x6c, 0xa5, 0x0d, 0x29, 0xfd, 0xcc, 0xef, 0xf6, 0x2b, 0x92
   };
   Crypto_DataBlob msgBlob = {
      .data = reinterpret_cast<uint8_t *>(plainText),
      .len = sizeof(plainText)
   };

   uint8_t pubKeyText[] = {
      0x2d, 0x2d, 0x2d, 0x2d, 0x2d, 0x42, 0x45, 0x47, 0x49, 0x4e, 0x20, 0x52, 0x53, 0x41, 0x20, 0x50,
      0x55, 0x42, 0x4c, 0x49, 0x43, 0x20, 0x4b, 0x45, 0x59, 0x2d, 0x2d, 0x2d, 0x2d, 0x2d, 0x0a, 0x4d,
      0x49, 0x47, 0x4a, 0x41, 0x6f, 0x47, 0x42, 0x41, 0x4b, 0x72, 0x55, 0x74, 0x74, 0x64, 0x76, 0x73,
      0x2b, 0x62, 0x6e, 0x4d, 0x2f, 0x6f, 0x4e, 0x75, 0x39, 0x45, 0x42, 0x78, 0x35, 0x64, 0x49, 0x6d,
      0x61, 0x70, 0x52, 0x67, 0x4d, 0x6a, 0x4b, 0x41, 0x38, 0x51, 0x48, 0x4b, 0x61, 0x75, 0x2f, 0x6c,
      0x58, 0x50, 0x50, 0x68, 0x76, 0x38, 0x30, 0x69, 0x59, 0x4c, 0x46, 0x2b, 0x79, 0x35, 0x35, 0x0a,
      0x6d, 0x42, 0x2f, 0x38, 0x2b, 0x4b, 0x68, 0x34, 0x34, 0x43, 0x2b, 0x5a, 0x76, 0x6f, 0x78, 0x5a,
      0x66, 0x38, 0x78, 0x34, 0x6e, 0x78, 0x6f, 0x71, 0x76, 0x4f, 0x6f, 0x73, 0x32, 0x44, 0x55, 0x69,
      0x51, 0x44, 0x4f, 0x4a, 0x35, 0x63, 0x57, 0x68, 0x5a, 0x62, 0x4d, 0x71, 0x4d, 0x42, 0x71, 0x62,
      0x39, 0x30, 0x4e, 0x39, 0x63, 0x2f, 0x44, 0x51, 0x67, 0x39, 0x34, 0x63, 0x52, 0x7a, 0x35, 0x66,
      0x0a, 0x68, 0x55, 0x66, 0x6d, 0x66, 0x6d, 0x54, 0x41, 0x46, 0x6a, 0x5a, 0x53, 0x33, 0x78, 0x6c,
      0x78, 0x77, 0x6e, 0x50, 0x77, 0x66, 0x66, 0x39, 0x71, 0x44, 0x79, 0x4c, 0x63, 0x5a, 0x55, 0x6b,
      0x6e, 0x64, 0x43, 0x30, 0x50, 0x77, 0x72, 0x6c, 0x38, 0x72, 0x70, 0x4b, 0x7a, 0x50, 0x47, 0x63,
      0x71, 0x4e, 0x67, 0x33, 0x5a, 0x41, 0x67, 0x4d, 0x42, 0x41, 0x41, 0x45, 0x3d, 0x0a, 0x2d, 0x2d,
      0x2d, 0x2d, 0x2d, 0x45, 0x4e, 0x44, 0x20, 0x52, 0x53, 0x41, 0x20, 0x50, 0x55, 0x42, 0x4c, 0x49,
      0x43, 0x20, 0x4b, 0x45, 0x59, 0x2d, 0x2d, 0x2d, 0x2d, 0x2d, 0x0a,
   };

   Crypto_DataBlob keyBlob = {
      .data = reinterpret_cast<uint8_t *>(pubKeyText),
      .len = sizeof(pubKeyText)
   };

   uint8_t signText[] = {
      0x1f, 0xe3, 0xcf, 0x8d, 0x94, 0xb4, 0xa0, 0x9e, 0xf1, 0x0c, 0x38, 0x59, 0xcb, 0x5b, 0x89, 0xc9,
      0x66, 0x8b, 0xfd, 0x8d, 0x1e, 0x37, 0xfa, 0x5e, 0x1b, 0xb1, 0x51, 0x07, 0xf1, 0xb0, 0x7d, 0x18,
      0x2d, 0x82, 0x2a, 0x04, 0xa4, 0x4e, 0x94, 0x7e, 0x76, 0xb8, 0xa4, 0x78, 0x90, 0x2f, 0x43, 0x1d,
      0x95, 0x80, 0xd7, 0xb3, 0x46, 0x4d, 0x58, 0x4b, 0xcd, 0x1f, 0x1d, 0xb3, 0x1f, 0x6b, 0x15, 0xd8,
      0x33, 0x51, 0x1d, 0x36, 0x12, 0x39, 0x92, 0xb4, 0x4d, 0xe2, 0x89, 0x26, 0x01, 0xe9, 0x1f, 0xc0,
      0x9c, 0x7c, 0xd8, 0xeb, 0x47, 0xff, 0xfb, 0x5d, 0x98, 0x9a, 0x02, 0x6a, 0x16, 0x37, 0xb1, 0xf5,
      0x08, 0x4d, 0xd7, 0xa0, 0xf2, 0x9e, 0xbe, 0x4b, 0x54, 0x77, 0x94, 0x95, 0x4b, 0x97, 0x10, 0x22,
      0x49, 0xa5, 0x2e, 0x05, 0x86, 0xfd, 0x6f, 0x9a, 0x40, 0xe6, 0x43, 0xab, 0xc5, 0xbc, 0xac, 0x21,
   };

   Crypto_DataBlob signBlob = {
      .data = reinterpret_cast<uint8_t *>(signText),
      .len = sizeof(signText)
   };
   
   // Key pair
   OH_Crypto_ErrCode ret = CRYPTO_SUCCESS;
   ret = OH_CryptoAsymKeyGenerator_Create((const char *)"RSA2048", &keyCtx);
   if (ret != CRYPTO_SUCCESS) {
      return ret;
   }
   ret = OH_CryptoAsymKeyGenerator_Convert(keyCtx, CRYPTO_PEM, &keyBlob, nullptr, &keyPair);
   if (ret != CRYPTO_SUCCESS) {
      OH_CryptoAsymKeyGenerator_Destroy(keyCtx);
      return ret;
   }
   OH_CryptoPubKey *pubKey = OH_CryptoKeyPair_GetPubKey(keyPair);
   // verify
   ret = OH_CryptoVerify_Create((const char *)"RSA1024|PKCS1|SHA256|Recover", &verify);
   if (ret != CRYPTO_SUCCESS) {
      OH_CryptoVerify_Destroy(verify);
      OH_CryptoAsymKeyGenerator_Destroy(keyCtx);
      return ret;
   }
   ret = OH_CryptoVerify_Init(verify, pubKey);
   if (ret != CRYPTO_SUCCESS) {
      OH_CryptoVerify_Destroy(verify);
      OH_CryptoAsymKeyGenerator_Destroy(keyCtx);
      return ret;
   }
   Crypto_DataBlob rawSignData = {.data = nullptr, .len = 0};
   ret = OH_CryptoVerify_Recover(verify, (Crypto_DataBlob *)&signBlob, &rawSignData);
   if (ret != CRYPTO_SUCCESS) {
      OH_CryptoVerify_Destroy(verify);
      OH_CryptoAsymKeyGenerator_Destroy(keyCtx);
      return ret;
   }

   OH_CryptoVerify_Destroy(verify);
   OH_CryptoAsymKeyGenerator_Destroy(keyCtx);
   OH_CryptoKeyPair_Destroy(keyPair);
   return ret;
}
```