/*
 * S/MIME detached data decrypt example: rarely done but should the need
 * arise this is an example....
 */
#include <openssl/pem.h>
#include <openssl/cms.h>
#include <openssl/err.h>

int main(int argc, char **argv)
{
    BIO *in = NULL, *out = NULL, *tbio = NULL, *dcont = NULL;
    X509 *rcert = NULL;
    EVP_PKEY *rkey = NULL;
    CMS_ContentInfo *cms = NULL;
    int ret = 1;

    OpenSSL_add_all_algorithms();
    ERR_load_crypto_strings();

    /* Read in recipient certificate and private key */
    tbio = BIO_new_file("signer.pem", "r");

    if (!tbio)
        goto err;

    rcert = PEM_read_bio_X509(tbio, NULL, 0, NULL);

    BIO_reset(tbio);

    rkey = PEM_read_bio_PrivateKey(tbio, NULL, 0, NULL);

    if (!rcert || !rkey)
        goto err;

    /* Open PEM file containing enveloped data */

    in = BIO_new_file("smencr.pem", "r");

    if (!in)
        goto err;

    /* Parse PEM content */
    cms = PEM_read_bio_CMS(in, NULL, 0, NULL);

    if (!cms)
        goto err;

    /* Open file containing detached content */
    dcont = BIO_new_file("smencr.out", "rb");

    if (!in)
        goto err;

    out = BIO_new_file("encrout.txt", "w");
    if (!out)
        goto err;

    /* Decrypt S/MIME message */
    if (!CMS_decrypt(cms, rkey, rcert, dcont, out, 0))
        goto err;

    ret = 0;

 err:

    if (ret) {
        fprintf(stderr, "Error Decrypting Data\n");
        ERR_print_errors_fp(stderr);
    }

    CMS_ContentInfo_free(cms);
    X509_free(rcert);
    EVP_PKEY_free(rkey);
    BIO_free(in);
    BIO_free(out);
    BIO_free(tbio);
    BIO_free(dcont);
    return ret;
}