loadrsa.c

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#include <stdio.h>
#include <openssl/rsa.h>

/* This is a simple program to generate an RSA private key.  It then
 * saves both the public and private key into a char array, then
 * re-reads them.  It saves them as DER encoded binary data.
 */

void callback(stage,count,arg)
int stage,count;
char *arg;
    {
    FILE *out;

    out=(FILE *)arg;
    fprintf(out,"%d",stage);
    if (stage == 3)
        fprintf(out,"\n");
    fflush(out);
    }

main()
    {
    RSA *rsa,*pub_rsa,*priv_rsa;
    int len;
    unsigned char buf[1024],*p;

    rsa=RSA_generate_key(512,RSA_F4,callback,(char *)stdout);

    p=buf;

    /* Save the public key into buffer, we know it will be big enough
     * but we should really check how much space we need by calling the
     * i2d functions with a NULL second parameter */
    len=i2d_RSAPublicKey(rsa,&p);
    len+=i2d_RSAPrivateKey(rsa,&p);

    printf("The public and private key are now both in a char array\n");
    printf("and are taking up %d bytes\n",len);

    RSA_free(rsa);

    p=buf;
    pub_rsa=d2i_RSAPublicKey(NULL,&p,(long)len);
    len-=(p-buf);
    priv_rsa=d2i_RSAPrivateKey(NULL,&p,(long)len);

    if ((pub_rsa == NULL) || (priv_rsa == NULL))
        ERR_print_errors_fp(stderr);

    RSA_free(pub_rsa);
    RSA_free(priv_rsa);
    }