X509_get0_pubkey_bitstr
ikey = X509_get0_pubkey_bitstr(issuer);
ikey = X509_get0_pubkey_bitstr(issuer);
keybstr = X509_get0_pubkey_bitstr(x);
ASN1_BIT_STRING *key = X509_get0_pubkey_bitstr(data);
ASN1_BIT_STRING *X509_get0_pubkey_bitstr(const X509 *x);