Time Series Analysis for Network Secruity

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Time Series Analysis for Network Security
Phil Roth
Data Scientist @ Endgame
mrphilroth.com

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First, an introduction. My history of Python
scientific computing, in function calls:

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os.path.walk
Physics Undergraduate @ PSU
AMANDA Neutrino Telescope

55
pylab.plot
Physics Graduate Student @ UMD
IceCube Neutrino Telescope

66
numpy.fft.fft
Radar Scientist @ User Systems, Inc.
Various Radar Simulations

77
pandas.io.parsers.read_csv
Side Projects
Scraping data from the web

88
sklearn.linear_model.LogisticRegression
Side Projects
Machine learning competitions

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(the rest of this talk…)
Data Scientist @ Endgame
Time Series Anomaly Detection

1010
Problem:
Highlight when recorded metrics deviate from
normal patterns.
for example: a high number of connections might be an
indication of a brute force attack
for example: a large volume of outgoing data might be an
indication of an exfiltration event

1111
Solution:
Build a system that can track and store
historical records of any metric. Develop an
algorithm that will detect irregular behavior
with minimal false positives.

1212
Gathering Data
kairos
kafka-python
pyspark
Building Models
classification
ewma
arima

1313
real time
stream
batch
historical
Redis
In memory
key-value data
store
HDFS
Large scale
distributed
data store
Kafka Topics
Distributed
message
passing
Data Sources
data flow

1414
kairos
A Python interface to backend storage databases
(redis in my case, others available) tailored for time
series storage.
Takes care of expiring data and different types of time
series (series, histogram, count, gauge, set).
Open sourced by Agora Games.
https://github.com/agoragames/kairos

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kairos
Example code:
from redis import Redis
from kairos import Timeseries
intervals = {"days" : {"step" : 60, "steps" : 2880},
"months" : {"step" : 1800, "steps" : 4032}}
rclient = Redis(“localhost”, 6379)
ktseries = Timeseries(rclient, type="histogram”, intervals=intervals)
ktseries.insert(metric_name, metric_value, timestamp)

1616
kafka-python
A Python interface to Apache Kafka, where Kafka is
publish-subscribe messaging rethought as a
distributed commit log.
Allows me to subscribe to the events as they come in
real time.
https://github.com/mumrah/kafka-python

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kafka-python
from kafka.client import KafkaClient
from kafka.consumer import SimpleConsumer
kclient = KafkaClient(“localhost:9092”)
kconsumer = SimpleConsumer(kclient, “timevault, “rawmsgs”)
for message in kconsumer :
insert_to_kairos(message)
Example code:

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pyspark
A Python interface to Apache Spark, where Spark is a
fast and general engine for large scale data
processing.
Allows me to fill in historical data to the time series
when I add or modify metrics.
http://spark.apache.org/

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pyspark
from pyspark import SparkContext, SparkConf
spark_conf = (SparkConf()
.setMaster(“localhost”)
.setAppName(“timevault-update”))
sc = SparkContext(conf=spark_conf)
rdd = (sc.textFile(hdfs_files)
.map(insert_to_kairos)
.count())
Example code:

2020
pyspark
from json import loads
import timevault as tv
from functools import partial
from pyspark import SparkContext, SparkConf
spark_conf = (SparkConf()
.setMaster(“localhost”)
.setAppName(“timevault-update”))
sc = SparkContext(conf=spark_conf)
rdd = (sc.textFile(tv.conf.hdfs_files)
.map(loads)
.flatMap(tv.flatten_message)
.flatMap(partial(tv.emit_metrics, metrics=tv.metrics_to_emit))
.filter(lambda tup : tup[2] < float(tv.conf.limit_time))
.mapPartitions(partial(tv.insert_to_kairos, conf=tv.conf)
.count())
Example code:

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the end result
from pandas import DataFrame, to_datetime
series = ktseries.series(metric_name, “months”, transform=transform)
ts, fields = zip(*series.items())
df = DataFrame({"data” : fields}, index=to_datetime(ts, unit="s"))

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building models
First naïve model is simply the mean and standard
deviation across all time.
blue: actual number of connections
green: prediction window
red: actual value exceeded standard deviation limit

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building models
Second slightly less naïve model is fitting a sine curve
to the whole series.

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classification
Both naïve models left a lot to be desired. Two simple
classifications would help us treat different types of
time series appropriately:
Does this metric show a weekly pattern (ie. different
behavior on weekends versus weekdays)?
Does this metric show a daily pattern?

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classification
Fit a sine curve to
the weekday and
weekend periods.
Ratio of the level of
those fits to
determine if
weekdays will be
divided from
weekends.
weekly

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classification weekly
from scipy.optimize import leastsq
def fitfunc(p, x) :
return (p[0] * (1 - p[1] * np.sin(2 * np.pi / (24 * 3600) * (x + p[2]))))
def residuals(p, y, x) :
return y - fitfunc(p, x)
def fit(tsdf) :
tsgb = tsdf.groupby(tsdf.timeofday).mean()
p0 = np.array([tsgb[“conns”].mean(), 1.0, 0.0])
plsq, suc = leastsq(residuals, p0, args=(tsgb[“conns”],
np.array(tsgb.index)))
return plsq

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classification weekly
def weekend_ratio(tsdf) :
tsdf['weekday'] = pd.Series(tsdf.index.weekday < 5, index=tsdf.index)
tsdf['timeofday'] = (tsdf.index.second + tsdf.index.minute * 60 +
tsdf.index.hour * 3600)
wdayplsq = fit(tsdf[tsdf.weekday == 1])
wendplsq = fit(tsdf[tsdf.weekdy == 0])
return wendplsq[0] / wdayplsq[0]
0 1cutoff 1 / cutoff
No weekly variation.

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classification
Weekly pattern.
No weekly pattern.
weekly

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classification
Take a Fourier
transform of the time
series, and inspect
the bins associated
with a frequency of a
day.
Use the ratio of
those bins to the first
(constant or DC
component) in order
to classify the time
series.
daily

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classification
Time series on
weekdays shown
with a strong daily
pattern.
Fourier transform
with bins around the
day frequency
highlighted.
daily

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classification
Time series on
weekends shown
with no daily pattern.
Fourier transform
with bins around the
day frequency
highlighted.
daily

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classification
def daily_ratio(tsdf) :
nbins = len(tsdf)
deltat = (tsdf.index[1] - tsdf.index[0]).seconds
deltaf = 1.0 / (len(tsdf) * deltat)
daybin = int((1.0 / (24 * 3600)) / deltaf)
rfft = np.abs(np.fft.rfft(tsdf[“conns”]))
daily_ratio = np.sum(rfft[daybin - 1:daybin + 2]) / rfft[0]
return daily_ratio
daily
Find the bin
associated with the
frequency of a day
using:

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ewma
Exponentially weighted moving average:
The decay parameter is specified as a span, s, in
pandas, related to α by:
α = 2 / (s + 1)
A normal EWMA analysis is done when the metric
shows no daily pattern. A stacked EWMA analysis is
done when there is a daily pattern.

3434
ewma
def ewma_outlier(tsdf, stdlimit=5, span=15) :
tsdf[’conns_binpred’] = pd.ewma(tsdf[‘conns’], span=span).shift(1)
tsdf[’conns_binstd’] = pd.ewmstd(tsdf[‘conns’], span=span).shift(1)
tsdf[‘conns_stds’] = ((tsdf[‘conns’] – tsdf[’conns_binpred’]) /
tsdf[‘conns_binstd’])
tsdf[‘conns_outlier’] = (tsdf[‘conns_stds’].abs() > stdlimit)
return tsdf
normal

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ewma normal

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ewma
blue: actual response size
normal

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ewma
def stacked_outlier(tsdf, stdlimit=4, span=10) :
gbdf = tsdf.groupby(‘timeofday’)[colname]
gbdf = pd.DataFrame({‘conns_binpred’ : gbdf.apply(pd.ewma, span=span),
‘conns_binstd’ : gbdf.apply(pd.ewmstd, span=span)})
interval = tsdf.timeofday[1] - tsdf.timeofday[0]
nshift = int(86400.0 / interval)
gbdf = gbdf.shift(nshift)
tsdf = gbdf.combine_first(tsdf)
tsdf[‘conns_stds’] = ((tsdf[‘conns’] – tsdf[‘conns_binpred’]) /
tsdf[‘conns_binstd’])
tsdf[‘conns_outlier’] = (tsdf[‘conns_stds’].abs() > stdlimit)
return tsdf
stacked
Shift the EWMA
results by a day and
overlay them on the
original DataFrame.

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ewma
stacked

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arima
I am currently investigating using ARIMA
(autoregressive integrated moving average) models to
make better predictions.
I’m not convinced that this level of detail is necessary
for the analysis I’m doing, but I wanted to highlight
another cool scientific computing library that’s
available.

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arima
from statsmodels.tsa.arima_model import ARIMA
def arima_model_forecast(tsdf, p, d q) :
arima_model = ARIMA(tsdf[“conns”][:-1], (p, d, q)).fit()
forecast, stderr, conf_int = arima_model.forecast(1)
tsdf[“conns_binpred"][-1] = forecast[0]
tsdf[“conns_binstd"][-1] = stderr[0]
return tsdf

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arima
p = d = q = 1

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takeaways
Python provides simple and usable interfaces to most
data handling projects.
Combined, these interfaces can create a full data
analysis pipeline from collection to analysis.

Time Series Analysis for Network Secruity

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