Thread: SMIME digital signature

Hello,
I'm trying to write an app which digitally signs emails. The problem I have is that SMIME_write_PKCS7() won't output any MIME headers the email previously had. I tested it with mails from my client so the headers should be ok.

Here is the code:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <openssl/bio.h>
#include <openssl/pkcs7.h>
#include <openssl/pkcs12.h>
#include <openssl/x509.h>

/ * Arguments: to be signed email, PKCS#12 certificate with private key
 */
int main(int argc, char** argv) {

    if (argc < 3) exit(1);
    OpenSSL_add_all_algorithms();

    BIO *data = BIO_new_file(argv[1], "rb");
    if (!data) exit(1);

    BIO *p12file = BIO_new_file(argv[2], "rb");
    if (!p12file) exit(1);
    PKCS12 *p12 = d2i_PKCS12_bio(p12file, NULL);
    if (!p12) exit(1);

    X509 *signcert;
    EVP_PKEY *pkey;
    STACK_OF(X509) *ca;
    int ret = PKCS12_parse(p12, "", &pkey, &signcert, &ca);
    if (!ret) exit(1);

    PKCS7 *p7 = PKCS7_sign(signcert, pkey, ca, data, 0);
    if (!p7) exit(1);

    BIO *out = BIO_new_file("email.eml", "wb");
    if (!out) exit(1);

    ret = SMIME_write_PKCS7(out, p7, data, 0);
    if (!ret) exit(1);

    BIO_free(data);
    BIO_free(p12file);
    PKCS12_free(p12);
    PKCS7_free(p7);

    return (EXIT_SUCCESS);
}

Thank you for any advice I can get.

OpenSSL: Documents, SMIME_write_PKCS7(3)
Why is flags zero?
Why are you ignoring the return result?