security/CryptoArchitectureKit/crypto-rsa-sign-sig-verify-pkcs1-ndk.md

# Signing and Signature Verification with an RSA Key Pair (PKCS1 Mode) (C/C++)

<!--Kit: Crypto Architecture Kit-->
<!--Subsystem: Security-->
<!--Owner: @zxz--3-->
<!--Designer: @lanming-->
<!--Tester: @PAFT-->
<!--Adviser: @zengyawen-->

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)
```
## Signing Data
1. Call [OH_CryptoSign_Create](../../reference/apis-crypto-architecture-kit/capi-crypto-signature-h.md#oh_cryptosign_create) and specify the string parameter **'RSA1024|PKCS1|SHA256'** to create a **Sign** instance for signing.

2. Call [OH_CryptoSign_Init](../../reference/apis-crypto-architecture-kit/capi-crypto-signature-h.md#oh_cryptosign_init) to initialize the **Sign** instance by using the private key (**OH_CryptoPrivKey**).

3. Call [OH_CryptoSign_Update](../../reference/apis-crypto-architecture-kit/capi-crypto-signature-h.md#oh_cryptosign_update) to pass in the data to be signed. Currently, the amount of data to be passed in by a single **update** is not limited. You can determine how to pass in data based on the data volume. If the data size is small, you can simply call **OH_CryptoSign_Final** to pass in the full data.

4. Call [OH_CryptoSign_Final](../../reference/apis-crypto-architecture-kit/capi-crypto-signature-h.md#oh_cryptosign_final) to obtain the signed data.

5. Call [OH_CryptoSign_Destroy](../../reference/apis-crypto-architecture-kit/capi-crypto-signature-h.md#oh_cryptosign_destroy) to free the memory.

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

static OH_Crypto_ErrCode doTestRsaSignature() {
   OH_CryptoAsymKeyGenerator *keyCtx = nullptr;
   OH_CryptoKeyPair *keyPair = nullptr;
   OH_CryptoSign *sign = nullptr;
   Crypto_DataBlob signData = {.data = nullptr, .len = 0};

   uint8_t plainText[] = {
      0x43, 0x31, 0x7d, 0xb5, 0x85, 0x2e, 0xd4, 0xef, 0x08, 0x7a, 0x17, 0x96, 0xbc, 0x7c, 0x8f, 0x80,
      0x8c, 0xa7, 0x63, 0x7f, 0x26, 0x89, 0x8f, 0xf0, 0xfa, 0xa7, 0x51, 0xbd, 0x9c, 0x69, 0x17, 0xf3,
      0xd1, 0xb5, 0xc7, 0x12, 0xbf, 0xcf, 0x91, 0x25, 0x82, 0x23, 0x6b, 0xd6, 0x64, 0x52, 0x77, 0x93,
      0x01, 0x9d, 0x70, 0xa3, 0xf4, 0x92, 0x16, 0xec, 0x3f, 0xa7, 0x3c, 0x83, 0x8d, 0x40, 0x41, 0xfc,
   }; // Data to be verified, for reference only.
   Crypto_DataBlob msgBlob = {
      .data = reinterpret_cast<uint8_t *>(plainText),
      .len = sizeof(plainText)
   };

   OH_Crypto_ErrCode ret = OH_CryptoAsymKeyGenerator_Create((const char *)"RSA2048", &keyCtx);
   if (ret != CRYPTO_SUCCESS) {
      return ret;
   }
   ret = OH_CryptoAsymKeyGenerator_Generate(keyCtx, &keyPair);
   if (ret != CRYPTO_SUCCESS) {
      OH_CryptoAsymKeyGenerator_Destroy(keyCtx);
      return ret;
   }

   OH_CryptoPrivKey *privKey = OH_CryptoKeyPair_GetPrivKey(keyPair);
   ret = OH_CryptoSign_Create((const char *)"RSA1024|PKCS1|SHA256", &sign);
   if (ret != CRYPTO_SUCCESS) {
      OH_CryptoAsymKeyGenerator_Destroy(keyCtx);
      OH_CryptoKeyPair_Destroy(keyPair);
      return ret;
   }

   ret = OH_CryptoSign_Init(sign, privKey);
   if (ret != CRYPTO_SUCCESS) {
      OH_CryptoSign_Destroy(sign);
      OH_CryptoKeyPair_Destroy(keyPair);
      OH_CryptoAsymKeyGenerator_Destroy(keyCtx);
      return ret;
   }
   ret = OH_CryptoSign_Update(sign, &msgBlob);
   if (ret != CRYPTO_SUCCESS) {
      OH_CryptoSign_Destroy(sign);
      OH_CryptoKeyPair_Destroy(keyPair);
      OH_CryptoAsymKeyGenerator_Destroy(keyCtx);
      return ret;
   }
   ret = OH_CryptoSign_Final(sign, nullptr, &signData);
   if (ret != CRYPTO_SUCCESS) {
      OH_CryptoSign_Destroy(sign);
      OH_CryptoKeyPair_Destroy(keyPair);
      OH_CryptoAsymKeyGenerator_Destroy(keyCtx);
      return ret;
   }

   OH_CryptoSign_Destroy(sign);
   OH_CryptoAsymKeyGenerator_Destroy(keyCtx);
   OH_CryptoKeyPair_Destroy(keyPair);
   return CRYPTO_SUCCESS;
}
```

## Verifying the Signature

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

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

3. Call [OH_CryptoVerify_Update](../../reference/apis-crypto-architecture-kit/capi-crypto-signature-h.md#oh_cryptoverify_update) to pass in the data to be verified.
   Currently, the amount of data to be passed in by a single **OH_CryptoVerify_Update** is not limited. You can determine how to pass in data based on the data volume.

   - If a small amount of data is to be verified, you can directly call [OH_CryptoVerify_Final](../../reference/apis-crypto-architecture-kit/capi-crypto-signature-h.md#oh_cryptoverify_final) after **OH_CryptoVerify_Init()**.
   - If a large amount of data is to be verified, call **OH_CryptoVerify_Update()** multiple times to [pass in data by segment](crypto-rsa-sign-sig-verify-pkcs1-by-segment-ndk.md).

4. Call [OH_CryptoVerify_Final](../../reference/apis-crypto-architecture-kit/capi-crypto-signature-h.md#oh_cryptoverify_final) to verify the signature.

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

static bool doTestRsaSignature()
{
   OH_CryptoAsymKeyGenerator *keyCtx = nullptr;
   OH_CryptoKeyPair *keyPair = nullptr;
   OH_CryptoVerify *verify = nullptr;

   uint8_t plainText[] = {
      0x43, 0x31, 0x7d, 0xb5, 0x85, 0x2e, 0xd4, 0xef, 0x08, 0x7a, 0x17, 0x96, 0xbc, 0x7c, 0x8f, 0x80,
      0x8c, 0xa7, 0x63, 0x7f, 0x26, 0x89, 0x8f, 0xf0, 0xfa, 0xa7, 0x51, 0xbd, 0x9c, 0x69, 0x17, 0xf3,
      0xd1, 0xb5, 0xc7, 0x12, 0xbf, 0xcf, 0x91, 0x25, 0x82, 0x23, 0x6b, 0xd6, 0x64, 0x52, 0x77, 0x93,
      0x01, 0x9d, 0x70, 0xa3, 0xf4, 0x92, 0x16, 0xec, 0x3f, 0xa7, 0x3c, 0x83, 0x8d, 0x40, 0x41, 0xfc,
   }; // Data to be verified, for reference only.
   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, 0x4d, 0x78, 0x63, 0x44, 0x4d, 0x6f, 0x61, 0x59,
      0x52, 0x58, 0x6f, 0x78, 0x65, 0x69, 0x33, 0x49, 0x6d, 0x33, 0x33, 0x78, 0x4a, 0x76, 0x61, 0x73,
      0x63, 0x43, 0x62, 0x77, 0x31, 0x6f, 0x73, 0x63, 0x32, 0x56, 0x56, 0x69, 0x47, 0x6a, 0x56, 0x47,
      0x47, 0x4a, 0x37, 0x6c, 0x75, 0x4e, 0x41, 0x58, 0x6b, 0x6a, 0x73, 0x56, 0x46, 0x64, 0x35, 0x0a,
      0x58, 0x37, 0x4c, 0x4d, 0x6c, 0x46, 0x34, 0x63, 0x35, 0x5a, 0x75, 0x59, 0x2f, 0x61, 0x69, 0x57,
      0x77, 0x70, 0x54, 0x69, 0x63, 0x62, 0x67, 0x49, 0x33, 0x43, 0x66, 0x50, 0x6f, 0x32, 0x6a, 0x6c,
      0x52, 0x74, 0x67, 0x41, 0x46, 0x6b, 0x44, 0x71, 0x7a, 0x4b, 0x53, 0x46, 0x62, 0x46, 0x47, 0x51,
      0x6b, 0x43, 0x6e, 0x64, 0x63, 0x2b, 0x54, 0x59, 0x6b, 0x5a, 0x42, 0x32, 0x70, 0x45, 0x6f, 0x72,
      0x0a, 0x7a, 0x73, 0x61, 0x56, 0x58, 0x77, 0x5a, 0x47, 0x45, 0x34, 0x41, 0x43, 0x70, 0x59, 0x35,
      0x79, 0x65, 0x66, 0x49, 0x44, 0x6c, 0x45, 0x57, 0x49, 0x51, 0x4f, 0x6a, 0x59, 0x4b, 0x2f, 0x6c,
      0x58, 0x71, 0x7a, 0x48, 0x47, 0x69, 0x4f, 0x69, 0x32, 0x75, 0x4a, 0x45, 0x75, 0x44, 0x43, 0x50,
      0x6a, 0x51, 0x64, 0x6a, 0x54, 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,
   }; // Public key in DER format, for reference only.

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

   uint8_t signText[] = {
      0x68, 0x2f, 0x3b, 0xe6, 0xa6, 0x5c, 0xb8, 0x60, 0xd4, 0xe1, 0x64, 0xa7, 0xd8, 0x0c, 0x9c, 0x89,
      0x39, 0xb4, 0xf0, 0xb7, 0xad, 0xb5, 0x8a, 0x71, 0x04, 0xf1, 0xa5, 0x63, 0xdd, 0x32, 0x6a, 0x44,
      0xeb, 0xff, 0xb7, 0xe6, 0x85, 0xe5, 0xa5, 0x55, 0x5d, 0x5b, 0x28, 0x53, 0x63, 0xe4, 0xb3, 0xb9,
      0xa8, 0x70, 0xc8, 0x8f, 0xcd, 0x21, 0x8d, 0xe6, 0x1f, 0xe5, 0x78, 0x34, 0xd3, 0x45, 0x0c, 0x9c,
      0x7a, 0x22, 0x1b, 0x63, 0x55, 0xca, 0x14, 0xa5, 0x0c, 0x7a, 0x40, 0x8e, 0xa1, 0x14, 0x78, 0xa1,
      0xf1, 0x36, 0x78, 0xbd, 0xba, 0x37, 0x3b, 0x5b, 0xb0, 0x8e, 0xb3, 0x4a, 0x9b, 0x1b, 0x0c, 0xfa,
      0xfa, 0xc7, 0x9f, 0xb1, 0x35, 0x48, 0x82, 0x73, 0xf8, 0x6b, 0xd4, 0x76, 0x33, 0x5c, 0xed, 0x9c,
      0xd8, 0x4b, 0xc9, 0x92, 0xa0, 0x3f, 0x6e, 0xba, 0x78, 0x2e, 0x80, 0x78, 0x1e, 0x74, 0xa0, 0x47,
   }; // Signature data, for reference only.

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

   // keypair
   OH_Crypto_ErrCode ret = CRYPTO_SUCCESS;
   ret = OH_CryptoAsymKeyGenerator_Create((const char *)"RSA2048", &keyCtx); // Create an asymmetric key generator.
   if (ret != CRYPTO_SUCCESS) {
      return false;
   }
   ret = OH_CryptoAsymKeyGenerator_Convert(keyCtx, CRYPTO_PEM, &keyBlob, nullptr, &keyPair); // Convert the public key in PEM format to OH_CryptoKeyPair.
   if (ret != CRYPTO_SUCCESS) {
      OH_CryptoAsymKeyGenerator_Destroy(keyCtx);
      return false;
   }
   OH_CryptoPubKey *pubKey = OH_CryptoKeyPair_GetPubKey(keyPair); // Obtain the public key.
   // verify
   ret = OH_CryptoVerify_Create((const char *)"RSA1024|PKCS1|SHA256", &verify); // Create a Verify instance.
   if (ret != CRYPTO_SUCCESS) {
      OH_CryptoVerify_Destroy(verify);
      OH_CryptoAsymKeyGenerator_Destroy(keyCtx);
      return false;
   }
   ret = OH_CryptoVerify_Init(verify, pubKey); // Use the public key to initialize the Verify instance.
   if (ret != CRYPTO_SUCCESS) {
      OH_CryptoVerify_Destroy(verify);
      OH_CryptoAsymKeyGenerator_Destroy(keyCtx);
      return false;
   }
   bool res = OH_CryptoVerify_Final(verify, &msgBlob, &signBlob); // Verify the signature of the data.
   if (res != true) {
      OH_CryptoVerify_Destroy(verify);
      OH_CryptoAsymKeyGenerator_Destroy(keyCtx);
      return false;
   }

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