How to load a PKCS#12 file in OpenSSL programmatically? - c

Question

In an SSL Server Application based on OpenSSL, how can we load a PKCS#12 file programmatically?
Also, can I load a PKCS#12 file having Certificate, Key & CAs in the same file in OpenSSL?

Answer 1

Yes you can load a PKCS#12 file containing certificate, key and CAs in the same file with OpenSSL.
Use d2i_PKCS12_fp() or d2i_PKCS12_bio() to load the PKCS#12 file.
Optionally use PKCS12_verify_mac() to verify the password.
Use PKCS12_parse() which decrypts and extracts key, certificate and CA chain for you.
From openssl-1.0.0d/demos/pkcs12/pkread.c:
#include <stdio.h>
#include <stdlib.h>
#include <openssl/pem.h>
#include <openssl/err.h>
#include <openssl/pkcs12.h>
/* Simple PKCS#12 file reader */
int main(int argc, char **argv)
{
FILE *fp;
EVP_PKEY *pkey;
X509 *cert;
STACK_OF(X509) *ca = NULL;
PKCS12 *p12;
int i;
if (argc != 4) {
fprintf(stderr, "Usage: pkread p12file password opfile\n");
exit (1);
}
OpenSSL_add_all_algorithms();
ERR_load_crypto_strings();
if (!(fp = fopen(argv[1], "rb"))) {
fprintf(stderr, "Error opening file %s\n", argv[1]);
exit(1);
}
p12 = d2i_PKCS12_fp(fp, NULL);
fclose (fp);
if (!p12) {
fprintf(stderr, "Error reading PKCS#12 file\n");
ERR_print_errors_fp(stderr);
exit (1);
}
if (!PKCS12_parse(p12, argv[2], &pkey, &cert, &ca)) {
fprintf(stderr, "Error parsing PKCS#12 file\n");
ERR_print_errors_fp(stderr);
exit (1);
}
PKCS12_free(p12);
if (!(fp = fopen(argv[3], "w"))) {
fprintf(stderr, "Error opening file %s\n", argv[1]);
exit(1);
}
if (pkey) {
fprintf(fp, "***Private Key***\n");
PEM_write_PrivateKey(fp, pkey, NULL, NULL, 0, NULL, NULL);
}
if (cert) {
fprintf(fp, "***User Certificate***\n");
PEM_write_X509_AUX(fp, cert);
}
if (ca && sk_X509_num(ca)) {
fprintf(fp, "***Other Certificates***\n");
for (i = 0; i < sk_X509_num(ca); i++)
PEM_write_X509_AUX(fp, sk_X509_value(ca, i));
}
sk_X509_pop_free(ca, X509_free);
X509_free(cert);
EVP_PKEY_free(pkey);
fclose(fp);
return 0;
}

Answer 2

Be warned that the code writes the certs out as trusted certificates (encrypted).
If you want unencrypted certificates, change the calls to PEM_write_X509_AUX() to PEM_write_X509().

Answer 3

Try man SSL, which gives you a list of OpenSSL functions. Something like SSL_load_client_CA_file might suit your needs; it depends if the certificate is in a file on disk or already in memory. There are lots of helper functions, one of them will do the trick. Also check out man PEM for PEM handling routines.
Edit: Hm, maybe a combination of d2i_PKCS12_fp and PKCS12_parse (both available from <openssl/pkcs12.h>) lets you read a certificate from file and parse it.