OpenSSL::OCSP::CertificateId#issuer_key_hash

static VALUE
ossl_ocspcid_get_issuer_key_hash(VALUE self)
{
    OCSP_CERTID *id;
    ASN1_OCTET_STRING *key_hash;
    VALUE ret;

    GetOCSPCertId(self, id);
    OCSP_id_get0_info(NULL, NULL, &key_hash, NULL, id);

    ret = rb_str_new(NULL, ASN1_STRING_length(key_hash) * 2);
    ossl_bin2hex(ASN1_STRING_get0_data(key_hash), RSTRING_PTR(ret),
                 ASN1_STRING_length(key_hash));

    return ret;
}