Re: DER-encoded issuer name

[Dmitri Bogutski]

....
ASN1_INTEGER *serial;
....
serial = X509_get_serialNumber(x);

What function should be called for using 'serial->data' as DER-encoded string?

Use the normal i2d_ASN1_INTEGER() function, i.e. (without
error checking):
    int len;
    unsigned char *buf, *p;

    len = i2d_ASN1_INTEGER(serial, 0);
    buf = OPENSSL_malloc(len);
    p = buf;
    i2d_ASN1_INTEGER(serial, &p);
after that buf points to the DER encoded ASN1 integer
(see FAQ: "How do I read or write a DER encoded ...").

Thanks for the detailed answer, but here still some questions.
I have made the following:
...
ASN1_INTEGER *serial;
int len;
unsigned char *buf, *p;
...
serial = X509_get_serialNumber(x); /* serial->length = 4 */
len = i2d_ASN1_INTEGER(serial, 0); /* len = 6 */
buf = OPENSSL_malloc(len);
p = buf;
i2d_ASN1_INTEGER(serial, &p);

Now 'buf' points to the '02 04 3C D1 12 2B', but serial number is '3C D1 12 2B'. How correctly to get serial number?
I looked OpenSSL's sources and comment to i2d_ASN1_INTEGER says: 'Output ASN1 INTEGER including tag+length'.
If I suppose correctly, '02 04' is a tag, if so what means this tag and how it to truncate?

Thanks,
Dmitry

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