Save X509 certificate to a file

Question

I am working on a HTTPS client and I managed to establish a secure connection and get the X509 certificate using:
X509 *cert = SSL_get_certificate(ssl); (ssl is SSL*).

How do I save the certificate to a file? Also, I need to get "Subject DN" and "Issuer DN" fields from the certificate.

Answer 1

-- How do I save the certificate to a file?

#include <openssl/pem.h>
int PEM_write_X509(FILE *fp, X509 *x);

-- Also, I need to get "Subject DN" and "Issuer DN" fields from the certificate.

#include <openssl/x509.h>
X509_NAME *     X509_get_issuer_name(X509 *a);
X509_NAME *     X509_get_subject_name(X509 *a); 

Answer 2

To encode the certificate into a file you can use this OpenSSL function:

int i2d_X509_fp(X509 *x, FILE *fp);

It encodes the X509 structure pointed by x into file using the DER encoding. More details on the OpenSSL API reference.