RSA Encryption/Decryption.

[Layla]

Hi all,

 

I'm trying to develop a C++ application to encrypt and decrypt data using RSA public key cryptography scheme. I have generated the public/private keys using OpenSSL command line tool. The following C++ code should read a public key, encrypt data, read private key and decrypt the data:

********************************************************************

#include <winsock2.h>
#include <iostream.h>
#include <openssl/rand.h>
#include <openssl/rsa.h>
#include <openssl/engine.h>

 

 

int main()
{ 

 char *message ="Hello World!";  
 RSA  *apub;
 RSA  *aprivate;
 FILE *f;
 int ret;
 unsigned char *buf;
 unsigned char *e_data;
 unsigned char *clear_text;
 

 //Get key
 f= fopen("a_rsa_public","rb");
 if(f == NULL)
 {
  printf("\nError opening public key file");
  return -1;
 }
 else
  printf("\n Public key file opened");

 

//load the key
 if ( fread(&apub,sizeof apub,1,f) != 1)
 {
  printf("\nError reading public key");
  return -1;
 }
 else
  printf("\nPublic key read");

 

 //close the key file
 fclose(f);

  
 buf = (unsigned char *) malloc(strlen(message)); 
 memcpy(buf,message,strlen(message));
 
 e_data = (unsigned char *) malloc(RSA_size(apub)); // THIS is where i get a run time error
 

//encrypt data

RSA_public_encrypt(strlen(message),buf, e_data, apub, RSA_PKCS1_OAEP_PADDING);

 //------------------decrypt
 //Get key
 f= fopen("a_rsa_private","rb");
 if(f == NULL)
 {
  printf("\nError opening private key file");
  return -1;
 }

 //load the key
  ret = fread(&aprivate,sizeof(aprivate),1,f);

 //close the key file
 fclose(f);

 

//make sure we loaded ok
 if(ret != 1)
 {
  printf("\nError reading private key");
  return -1;
 }

 clear_text= (unsigned char *) malloc(strlen(message));
 RSA_private_decrypt(strlen((char*)e_data), e_data, clear_text, aprivate, RSA_PKCS1_OAEP_PADDING);

 return 0;
}

 

*******************************************************************************

At first I used to get a run time error in the RSA_public_encrypt(...); and I figured caused I had e_data initialized as:

e_data = (unsigned char *) malloc(strlen(message)*4);

 

So instead I used :

e_data = (unsigned char *) malloc(RSA_size(apub));

and now I'm getting a run time as this line is encountered.

 

I'm sure someone with experience would be able to spot my mistake.

 

I thank you all in advance for your help.

 

 

 

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