RSA encryption size and copying to Char Buffer ?

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Hi,
I have done RSA ENCRYPTION using C program and got the encrypted message in character buffer. I need to send this encrypted message to a different system in a binary format.
I have added the RSA_size(rsa) command and free( encrypted). But I am getting coredump on RSA_size(rsa). So I removed it.
Also I want to calculate the size of encrypted variable. But I tried with strlen(), I am getting different length value while execution. 'Bufsize' value always = 256 but the encrypted character value always varies with different values. It should be 256, I hope ...Please suggest.
I need to copy this encrypted value into another character buffer and I have to send as a packet via TCP / IP. I am confused while copying to character buffer.
Need some idea on the above.
Thanks in Advance
Pattabi.

XML

#include <stdio.h>
#include <openssl/rsa.h>
#include <openssl/pem.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <time.h>
#include <string.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <dirent.h>
#include <ctype.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <sys/time.h>
#include <signal.h>
#include <stdlib.h>
#include <memory.h>
#include <string.h>

void EncrCardPin(char *,char *);
int main(int argc, char *argv[])
{

    char* pin="2345";
    //char storebuf[256];

    unsigned char* storebuf = (unsigned char *) malloc(500);
    memset(storebuf,'\0',sizeof(storebuf));

    EncrCardPin(pin,storebuf);

    return 0;
}

void EncrCardPin(char *pin,char *encpin)
 {
    int bufSize;
    char *pubname="publkey.pem"; /***** 2048 bit key********/

    FILE *keyfile = NULL;
    RSA* rsa=NULL;
    FILE *test = NULL;

    //int len=RSA_size(rsa) - 11; /********* Giving Core Dump Always *******/

    unsigned char* encrypted = (unsigned char *) malloc(500);

    test=fopen("test.bin","wb");

    printf("Opening the puclic key file: [%s]\n",pubname);
    keyfile = fopen(pubname, "r");

    if (!keyfile)
    { printf("error occured while reading public key file");    }

    rsa =   PEM_read_RSA_PUBKEY(keyfile, NULL, NULL, NULL);

    if (rsa == NULL)
    {       printf("Badness has occured! Did not read  public key file\n"); }
    else
    {       printf("Opened public key file OK!\n"); }

    bufSize = RSA_public_encrypt(strlen(pin), (unsigned char *) pin, encpin, rsa, RSA_PKCS1_PADDING);
    if (bufSize == -1)
    {   printf("Badness has occured! encryption failed\n");
        RSA_free(rsa);
    }
    else
    {
        printf("Encrypted the message OK! \n");
        fprintf(test,"%s",encpin);
        printf("The buffersize is : [%d]\n ================",bufSize);
    }
    free(encrypted);
    RSA_free(rsa);
    fclose(keyfile);
    fclose(test);


 }

[edit]Comment edited to remove hyphen followed by greater than symbol. This allows the rest of your code to be visible! - OriginalGriff [/edit]

Posted 12-Apr-11 22:55pm

rprtech

Updated 12-Apr-11 23:34pm

OriginalGriff

v2

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OriginalGriff · Answer 1 · 2011-04-12T23:36:00

The problem is likely to be here:

RSA* rsa=NULL;
FILE *test = NULL;
//int len=RSA_size(rsa) - 11; /********* Giving Core Dump Always *******/

Since RSA_size requires a pointer to an RSA, handing it a null, will probably give a memory access violation, triggering a core dump.

Try handing it a pointer to an actual RSA object!

[edit]Typo, I missed the "_size" off "RSA_size" - OriginalGriff[/edit]

"Hi ,

I have modified like this
RSA *rsa;
int len = RSA_size(rsa);
But still gives coredump message as "in BN_num_bits()". Don't know from where its referring this . Any clue ????"
Yes - read what I said.

rsa is a variable, which holds a pointer to an RSA object.

You do not assign a valid RSA object to the rsa variable.

When RSA_Size tries to use the RSA object you hand it the pointer of, it accesses the wrong memory.

Would you expect this to work?

int *i;
*i = 6;

Or should it be this?

int *i;
int j;
i = &j;
*i = 6;