char * to ASN1_INTEGER

Question

For PKI certificate generation , and for setting up serial number , I used RAND_bytes to get 20 bytes of random serial number, now I wanted this char * to be set to serial number of certificate , which seems to be of type ASN1_INTEGER *

Tried ASN1_TYPE_set_octetstring(ASN1_TYPE *, unsigned char *, len) but since it takes ASN1_TYPE * and not ASN1_INTEGER* it gave a crash

How do I convert between unsigned char * to ASN1_INTEGER ?

Thanks,

Answer 1

I'm fairly sure this is what you're looking for, but I could be wrong. If you want to have a 20-byte ASN1_INTEGER one way to do that is sending it through the BIGNUM library first:

unsigned char data[20] = {0};
RAND_bytes(data, sizeof(data));
data[0] &= 0x7F;

// build big number from our bytes
BIGNUM* bn = BN_new();
BN_bin2bn(data, sizeof(data), bn);

// build the ASN1_INTEGER from our BIGNUM
ASN1_INTEGER* asnInt = ASN1_INTEGER_new();
BN_to_ASN1_INTEGER(bn, asnInt);

// TODO: use your ASN1_INTEGER

// cleanup
ASN1_INTEGER_free(asnInt);
BN_free(bn);