Question

I’m using openssl libraryes on client/server application, and i need to share public key with client.
this is the struct of packet:

typedef struct pack {
    char op[10];
    char message[1024];
    int id;
}packet;

and this is how extract the public key and put it in message field:

packet *send_pack
RSA *rsa,
const unsigned char *my_public_key;

my_public_key = malloc(1024);
send_pack = (packet*) malloc(sizeof (packet));
rsa = RSA_new();
rsa = RSA_generate_key(1024, 17, NULL, NULL);
i2d_RSAPublicKey(rsa, &my_public_key);
printf("my public key: %X\n", (unsigned int)my_public_key);
strcpy(send_pack->message, my_public_key);
printf("field message of send pack %X", (unsigned int)send_pack->message );

...

but the two printf print two similar value, but not the same (for example the first printf return A0B9092 and the second A0B944 ).
What’s wrong ?

Answer 1

There are multiple issues:

• You’re printing pointer addresses instead of contents
• You’re copying the key wrong since strcpy expects 0-terminated strings

For the first issue, you should note i2d_RSAPublicKey returns a length which you’re ignoring. So you should print:

int len = i2d_RSAPublicKey(...);
for (i = 0; i < len; i++)
    printf("%02x", my_public_key[i]);

For the second part, use memcpy instead:

memcpy(send_pack->message, my_public_key, len);