bro_beacons.bro - bad conversion to count


I am using the bro_beacons.bro script and it generating multiple errors like

1486782334.477425 error in /usr/local/bro/share/bro/site/bro_beacons.bro, line 46: bad conversion to count (double_to_count(interval_to_double(BEACON::collection[BEACON::i + (coerce 1 to int)] - BEACON::collection[BEACON::i])) and -3.57259)

Here is the script in question

#Author: Nick Hoffman / / @infoseckitten

#Description: A bro script to find beacons

module BEACON;

@load base/protocols/http

#this is our master collection, we’ll use this to store all our information

global master_collection: table[addr,addr] of vector of time &synchronized;

export {

redef enum Log::ID += { LOG };

type Info: record {

ts: time &log;

#id: conn_id &log;

local_host: addr &log;

remote_host: addr &log;

entropy: double &log;


global log_beacon: event(rec: Info);

# Add hosts to ignore with:

# redef BEACON::whitelist += {,}

const whitelist: set [subnet] = set() &redef;


event bro_init()


Log::create_stream(BEACON::LOG, [$columns=Info, $ev=log_beacon]);


function calculate_entropy(host: addr, server: addr): double


local collection = master_collection[host,server];

local entropy: count;

local length = |collection|;

local intervals = vector();

local pmf: table[time] of double;

local probs: table[time] of double;

local sum: double;

sum = 0;

for (i in collection) {

if ( i+1 >= length )


else {

intervals[i] = double_to_interval(double_to_count(interval_to_double(collection[i+1] - collection[i])));



#i don’t like this solution, oh well

for (i in intervals) {

if ( intervals[i] !in pmf )

pmf[intervals[i]] = 1;


pmf[intervals[i]] += 1;


#calculate the probabilities

for (i in intervals) {

probs[intervals[i]] = pmf[intervals[i]] / |intervals|;


for (k in probs) {

sum += probs[k] * (log10(probs[k]) / log10(2.0));


if (double_to_time(0.0) in probs) {

if (probs[double_to_time(0.0)] > 0.3)

sum = 4;


#debug statement

#print fmt(“host:%s,server:%s,entropy:%s,interval:%s”,host,server,|sum|,intervals);

return |sum|;


#we’ll start with http posts, in the case that

event http_request(c: connection, method: string, original_URI: string, unescaped_URI: string, version: string) {

#declare variables

local host: addr;

local server: addr;

local ts: time;

local uid: string;

local entropy_result: double;

for (sn in whitelist) {

if (c$id$resp_h in sn || c$id$orig_h in sn )



if ( method == “POST” || method == “GET” ) {

#grab the relevant information

host = c$id$orig_h;

server = c$id$resp_h;

ts = c$start_time;

uid = c$uid;

if ( [host,server] !in master_collection ){

master_collection[host,server] = vector(ts) ;


else {

master_collection[host,server][|master_collection[host,server]|] = ts;

if ( |master_collection[host,server]| > 12) {

entropy_result = calculate_entropy(host,server);

if (entropy_result < 0.75 ) {

print fmt("%s - beacon %s and %s", ts, host, server);

local rec: BEACON::Info = [$ts=ts, $entropy=entropy_result,$local_host=host,$remote_host=server];

Log::write(BEACON::LOG, rec);


master_collection[host,server] = vector();





Can anyone tell me how to solve this ?

The issue seems to be this line

intervals[i] = double_to_interval(double_to_count(interval_to_double(collection[i+1] - collection[i])));



Vikram Basu

The problem is that a negative number was passed to double_to_count; count
is an unsigned integer value and cannot represent that.

On a first glance, I am not quite sure why all those conversions take
place in the first place - it seems to convert from an interval to double,
then to count, and then back to interval. I would just try to either skip
the conversions altogether, or if the idea is to get rid of the positions
after the decimal place, to convert to int instead.

I hope that helps,