X509 structure to human readable string

Question

How would I go about converting a X509 certificate in C into human readable string. For example:

X509* cert;

into

-----BEGI         


        

Answer 1

Conversion of X509 structure to the string with PEM encoded certificate:

char *X509_to_PEM(X509 *cert) {

    BIO *bio = NULL;
    char *pem = NULL;

    if (NULL == cert) {
        return NULL;
    }

    bio = BIO_new(BIO_s_mem());
    if (NULL == bio) {
        return NULL;
    }

    if (0 == PEM_write_bio_X509(bio, cert)) {
        BIO_free(bio);
        return NULL;
    }

    pem = (char *) malloc(bio->num_write + 1);
    if (NULL == pem) {
        BIO_free(bio);
        return NULL;    
    }

    memset(pem, 0, bio->num_write + 1);
    BIO_read(bio, pem, bio->num_write);
    BIO_free(bio);
    return pem;
}

Conversion of PEM encoded certificate to the X509 structure:

X509 *PEM_to_X509(char *pem) {

    X509 *cert = NULL;
    BIO *bio = NULL;

    if (NULL == pem) {
        return NULL;
    }

    bio = BIO_new_mem_buf(pem, strlen(pem));
    if (NULL == bio) {
        return NULL;
    }

    cert = PEM_read_bio_X509(bio, NULL, NULL, NULL);
    BIO_free(bio);
    return cert;
}