Problem decoding DER buffer into X509 structure

Nick Brosnahan Mon, 11 Oct 2004 16:33:04 -0700

Hi-

I'm having trouble with the d2i_X509() call. I've googled all the errors that I get and I can't figure out what's going on. I'm using OpenSSL 0.9.7d.

Basically, I'm trying to read a cert off disk (PEM format). Then I convert it into a DER buffer using i2d_X509(). Sometime later, I need to convert the DER buffer back into an X509 structure using d2i_X509() and that's when the wheels come off the wagon.

I've attached a code snippet that shows the problem. Can anyone help me out?

Thanks,
Nick

all:    example.c
        gcc -o example -lcrypto example.c

#include <stdio.h>
#include <openssl/pem.h>
#include <openssl/x509.h>
#include <openssl/err.h>


int main(int argc, char** argv)
{
	int buflen = 200;
	char buf[buflen];
	unsigned long opensslerr = 0;

	/* This OpenSSL incantation is absolutely necessary */
	OpenSSL_add_all_algorithms();
	ERR_load_crypto_strings();

	FILE *fp = fopen("cacert.pem", "r");

	/* Load a cert off disk */
	X509 *cert = PEM_read_X509(fp, NULL, NULL, NULL);
	opensslerr = ERR_get_error();
	if (opensslerr != 0) 
	{
		ERR_error_string_n(opensslerr, buf, buflen);
		printf("PEM READ ERROR %s\n", buf);
		return -1;
	}

	fclose(fp);
	fp = NULL;

	/* Print out the subject and issuer */
	X509_NAME *name = X509_get_subject_name(cert);
	char *nameStr = X509_NAME_oneline(name, buf, buflen);
	printf ("Subject: %s\n", nameStr);
	name = X509_get_issuer_name(cert);
	nameStr = X509_NAME_oneline(name, buf, buflen);
	printf ("Issuer: %s\n", nameStr);

	/* Find out how long the cert is when converted to DER */
	int certlen = i2d_X509(cert, NULL);
	opensslerr = ERR_get_error();
	if (opensslerr != 0) {
		ERR_error_string_n(opensslerr, buf, buflen);
		printf("CERT DER LEN ERROR %s\n", buf);
		return -1;
	}

	printf("CertLen: %d\n", certlen);

	/* Allocate some space for it */
	unsigned char* certbuf = (unsigned char*) malloc(certlen);
	if (certbuf == NULL) 
	{
		printf("Unable to allocate memory for DER buffer");
		return -1;
	}

	/* Convert the X509 structure to a DER encoding */
	if (i2d_X509(cert, &certbuf) < 0) 
	{
		opensslerr = ERR_get_error();
		ERR_error_string_n(opensslerr, buf, buflen);
		printf("i2d ERROR %s\n", buf);
		return -1;
	}

	/* Turn right around and try to recreate the X509 from the DER */
	X509 *decodedcert = d2i_X509(NULL, &certbuf, certlen);
	if (decodedcert == NULL) {
		while ((opensslerr = ERR_get_error()) != 0) {
			ERR_error_string_n(opensslerr, buf, buflen);
			printf("d2i ERROR %s\n", buf);
		}
		return -1;
	}
}

Problem decoding DER buffer into X509 structure

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