I have a problem and no idea how I can solve it. I have a X.509v3 certificate with a custom OID (object identifier) in the ExtendedKeyUsage
extension. How can I extract all OIDs from the ExtendedKeyUsage
using OpenSSL 1.1.0?
For example, I created a certificate with 3 flags in the ExtendedKeyUsage extension:
"clientAuth, 1.3.6.1.5.5.7.3.103, timeStamping"
clientAuth
and timeStamping
are known for OpenSSL. The flag in the middle is my custom OID. I added all flags with the OpenSSL function X509V3_EXT_conf_nid()
. ok... as far as works all.
Now I tried to extract the OIDs with X509_get_extended_key_usage(cert)
, but i only get clientAuth
and timeStamping
.
Now I extracted the raw data from ExtendedKeyUsage as ASN1_OCTET_STRING like this:
int size;
unsigned char *data;
ASN1_OCTET_STRING *os;
X509_EXTENSION *ext;
// extracting data from certificate extension
ext = X509_get_ext(cert, 2);
os = X509_EXTENSION_get_data(ext);
size = ASN1_STRING_length(os);
data = ASN1_STRING_data(os);
This is the content of data
in hex: 30:1E:06:08:2B:06:01:05:05:07:03:02:06:08:2B:06:01:05:05:07:03:67:06:08:2B:06:01:05:05:07:03:08
.
If I decode this hex string with an external tool, then I get this:
Offset|Length|LenByte|
======+======+===================================================
0| 30| 1| SEQUENCE :
2| 8| 1| OBJECT_IDENTIFIER : '1.3.6.1.5.5.7.3.2' (id-kp-clientAuth)
12| 8| 1| OBJECT_IDENTIFIER : '1.3.6.1.5.5.7.3.103'
22| 8| 1| OBJECT_IDENTIFIER : '1.3.6.1.5.5.7.3.8' (id-kp-timeStamping)
My OID is available, but how I extract this OID in OpenSSL? Can I parse it ....and how? :(
Thanks you in advance.
I find a solution!
here is my quick-and-diry code:
// optional: we can set an OID name
OBJ_create("1.3.6.1.5.5.7.3.103", "myObjectShortName", "myObjectLongName");
// find the extendedKeyUsage
int extIndex = X509_get_ext_by_NID(cert, NID_ext_key_usage, -1);
if (extIndex < 0)
std::cerr << "extendedKeyUsage is not present";
// get the correct X.509 extension
X509_EXTENSION *ext = X509_get_ext(cert, extIndex);
if (!ext)
std::cerr << "'ext' is a nullptr";
// get the extendedKeyUsage
EXTENDED_KEY_USAGE *eku = static_cast<EXTENDED_KEY_USAGE*>(X509V3_EXT_d2i(ext));
if (!eku)
std::cerr << "'eku' is a nullptr";
// print all OIDs
for (int i = 0; i < sk_ASN1_OBJECT_num(eku); i++)
{
char buffer[100];
OBJ_obj2txt(buffer, sizeof(buffer), sk_ASN1_OBJECT_value(eku, i), 1); // get OID
std::cout << "eku flag " << i << ": " << buffer << "\t - ";
std::cout << OBJ_nid2ln(OBJ_obj2nid(sk_ASN1_OBJECT_value(eku, i))) << std::endl; // get OID name
}
// free used resource
if (eku)
EXTENDED_KEY_USAGE_free(eku);
Output:
eku flag 0: 1.3.6.1.5.5.7.3.2 - TLS Web Client Authentication
eku flag 1: 1.3.6.1.5.5.7.3.103 - myObjectLongName
eku flag 2: 1.3.6.1.5.5.7.3.8 - Time Stamping
maybe this code help someone else
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