[ACCEPTED]-Extract pem certificate information programmatically using openssl-pem

Accepted answer
Score: 13

The X509_print_ex family of functions is your answer.

#include <openssl/x509.h>
#include <openssl/pem.h>
#include <openssl/bio.h>

int main(int argc, char **argv)
    X509 *x509;
    BIO *i = BIO_new(BIO_s_file());
    BIO *o = BIO_new_fp(stdout,BIO_NOCLOSE);

    if((argc < 2) ||
       (BIO_read_filename(i, argv[1]) <= 0) ||
       ((x509 = PEM_read_bio_X509_AUX(i, NULL, NULL, NULL)) == NULL)) {
        return -1;

    X509_print_ex(o, x509, XN_FLAG_COMPAT, X509_FLAG_COMPAT);


Score: 7

As additional information related to this 5 question, in case of having a certificate 4 with the DER format instead of PEM; it is 3 also possible to extract the information 2 in a human readable mode using the following 1 code:

//Assuming that the DER certificate binary information is stored in
//a byte array (unsigned char) called "pData" whose size is "lenData"
X509* x509;
BIO* input = BIO_new_mem_buf((void*)pData, lenData);
//d2i_X509_bio: Decodes the binary DER certificate
//and parses it to a X509 structure
x509 = d2i_X509_bio(input, NULL);
if (x509 == NULL)
   //Error in d2i_X509_bio
    //"certificateFile" is the full path file
    //where to store the certificate information
    //in a human readable mode (instead of stdout)
    FILE* fd = fopen(certificateFile, "w+");
    BIO* output = BIO_new_fp(fd, BIO_NOCLOSE);
    X509_print_ex(output, x509, XN_FLAG_COMPAT, X509_FLAG_COMPAT);

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