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Alexandre Dulaunoy 2019-09-10 14:54:00 +02:00
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_posts/2019-09-12-Decaying-Of-Indicators.md
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# Problem statement
MISP being a P2P system, various users and organisations are sharing data, sometimes without even knowing each others. While having access to a lot of information is extremelly benificial for all parties, it, however, also induces challenges to deal with.
---
title: Decaying of Indicators - MISP improved model to expire indicators based on custom models
layout: post
featured: /assets/images/misp/blog/community-view.png
---
In this blogpost, we will mainly discuss about information **quality** and **freshness**, other issues like **trust**, **use-cases**, **interests**, etc. are partially taken into account but will not be presented. Nevertheless, these concepts are examined in this [paper](https://arxiv.org/abs/1902.03914) along with a detailed explanation of the solution we've choosen to tackle these issues.
# An improved and flexible model to expire indicators
MISP being a distributed system, various users and organisations are sharing data, sometimes without even knowing each others. While having access to a lot of information is extremely beneficial for all parties, it, however, also induces challenges to deal with.
In this blog post, we will mainly discuss about information **quality** and **freshness**, other issues like **trust**, **use-cases**, **interests**, etc. are partially taken into account but will not be presented. Nevertheless, these concepts are examined in this [paper](https://arxiv.org/abs/1902.03914) along with a detailed explanation of the solution we have chosen to tackle these issues.
Our main objective is to provide users a **simple yet customizable system** to automatically (or manually) mark an *Indicator Of Compromise* (or more generic, an *Attribute*) as **expired**.
Before getting started to show how the model presented in the paper is implemented in MISP, we first need to have a look at some concepts needed to better understand how components are working and tied together.
# The (potentially) annoying bits of theory
The solution currently supported in MISP is based on two components: ``base_score`` and ``score``. The idea is to have an initial fixed value called ``base_score`` taking into account the **quality** of an indicator; and a time-dependant ``score``, which decreases the more time passes.
A simplified version would be something like this:
@ -21,7 +29,8 @@ Where ``P`` is composed of ``parameters``:
**⚠** **It should be noted that everytime a [*Sightings*](https://www.circl.lu/doc/misp/sightings/) is added to an *Attribute*, the ``score`` is refresh to the ``base_score`` and a new decay is initiated from that point.**
# Polynomial Decaying Model built-in in MISP
We still have to see how the ``base_score`` is actually computed. In the built-in version of the *Decaying Model* in MISP, the ``base_score`` is computed from the *Taxonomies* and some weigths. Weights are a mean to prioritize extracted ``numerical_values`` from *Taxonomies* over others.
We still have to see how the ``base_score`` is actually computed. In the built-in version of the *Decaying Model* in MISP, the ``base_score`` is computed from the *Taxonomies* and some weight. Weights are a mean to prioritize extracted ``numerical_values`` from *Taxonomies* over others.
To give the intuition of how the ``base_score`` computation works, let's look at two examples. In these examples, the two *Taxonomies* used are
[*phishing*](https://github.com/MISP/misp-taxonomies/blob/master/phishing/machinetag.json) and [*admiralty-scale*](https://github.com/MISP/misp-taxonomies/blob/master/admiralty-scale/machinetag.json). Both of them contain *Tags* that have a ``numerical_value`` associated to them:
@ -34,7 +43,8 @@ So, if an *Attribute* only have one *Tag* attached, let's say ``admiralty-scale:
base_score = 100
```
Weights come into action when multiple *Tags* are attached to an *Attribute*. To make things a bit easier, let's suppose that both *Taxonomies* should have the same importance in regards to the *Attribute*'s score. Thus, the total weigth (100) will be shared, assigning both *Taxonomy* a weight of 50.
Weights come into action when multiple *Tags* are attached to an *Attribute*. To make things a bit easier, let's suppose that both *Taxonomies* should have the same importance in regards to the *Attribute*'s score. Thus, the total weight (100) will be shared, assigning both *Taxonomy* a weight of 50.
```
admiralty-scale = 50
phishing = 50
@ -49,16 +59,19 @@ Thus, the ``base_score`` of this *Attribute* will be ``87.50``.
# Short tutorial
Now that we've seen the basic concepts, let's have a look at how MISP implents these components. For these examples, we are using the default [phishing model](https://github.com/MISP/misp-decaying-models/blob/master/models/phishing-model.json) model on a **test** *Event*.
Now that we've seen the basic concepts, let's have a look at how MISP implements these components. For these examples, we are using the default [phishing model](https://github.com/MISP/misp-decaying-models/blob/master/models/phishing-model.json) model on a **test** *Event*.
## Practical integration in MISP
### Endpoint: ``events/view``
At the *Event* level, a new filtering button has been added to attach the real-time computed ``score`` of any *Attributes* that has been mapped to a *Model*.
<img src="../assets/images/misp/blog/decaying//dm-event.png" alt="Decaying Model index" width="700"/>
<img src="../assets/images/misp/blog/decaying/dm-event.png" alt="Decaying Model index" width="700"/>
### Endpoint: ``attribute/restSearch``
The ``attribute/restSearch`` endpoint has been updated and now supports four new parameters to filter out expired *Attributes* or play with the different available models.
- ``includeDecayScore`` **[bool]**: Attach the real-time computed ``score`` of the *Attribute* along with *Model(s)* informations
- ``excludeDecayed`` **[bool]**: Filter out all expired IOC
@ -83,29 +96,35 @@ Example
```
## Default and Custom Models
In MISP, Some *Decaying Models* called **Default Models** will be supplied by default. Similarly to *Taxonomies*, *Galaxies* or *misp-objects*, *Decaying Models* will have their [own repository](https://github.com/MISP/misp-decaying-models) and will have the possibility to be updated directly from the UI via a single click. **Default Models** are available to everyone, meaning that they can been viewed and customized by any users having a presence on the MISP instance.
**Custom Models** are user-defined models that are shared to other users. However, if desired, they can be hidden by turning off the sharing flag, similarly to the *Tag Collection* feature.
## Decaying Fine Tuning Tool: Setting parameters and mapping model to *Attribute* types
When creating a new *Decaying Model*, setting a parameters and viewing its impact should be as easy and straighforward as possible. To do so, few widgets are shipped with the latest version of MISP.
When creating a new *Decaying Model*, setting a parameters and viewing its impact should be as easy and straight forward as possible. To do so, few widgets are shipped with the latest version of MISP.
### Customizing lifetime and decay speed parameters
<video src="../assets/images/misp/blog/decaying//dm-tool.mp4" title="Decaying Model Fine Tuning Tool - Parameters" width="800" height="450" controls autoplay loop>
Your browser does not support the video tag.
</video>
### Setting the ``base_score``: Customizing Taxonomies' weigth
<video src="../assets/images/misp/blog/decaying//dm-bs.mp4" type="video/mp4" title="Decaying Model Fine Tuning Tool - Base score" width="800" height="450" controls autoplay loop>
<video src="../assets/images/misp/blog/decaying/dm-tool.mp4" title="Decaying Model Fine Tuning Tool - Parameters" width="800" height="450" controls autoplay loop>
Your browser does not support the video tag.
</video>
</video>
### Viewing scores and Simulating the model
<video src="../assets/images/misp/blog/decaying//dm-simulation.mp4" type="video/mp4" title="Decaying Model Simulation Tool" width="800" height="450" controls autoplay loop>
### Setting the ``base_score``: Customizing Taxonomies' weight
<video src="../assets/images/misp/blog/decaying/dm-bs.mp4" type="video/mp4" title="Decaying Model Fine Tuning Tool - Base score" width="800" height="450" controls autoplay loop>
Your browser does not support the video tag.
</video>
</video>
### Viewing scores and simulating the model
<video src="../assets/images/misp/blog/decaying/dm-simulation.mp4" type="video/mp4" title="Decaying Model Simulation Tool" width="800" height="450" controls autoplay loop>
Your browser does not support the video tag.
</video>
# Developer perspective: Creating a model using a different algorithm
The Built-in Polynomial *Decaying Model* implemented in MISP allows any user to customize various components to achieve fine-grained decay behaviors. Still, it is possible that our model doesn't encompass your specific use-case. Thanks to the implemented architecture, any other formulas or algorithms can be added and used in a straightforward way.
Steps to create a new decay algorithm:
@ -136,6 +155,7 @@ class Polynomial extends DecayingModelBase
```
# Outcomes
Evaluating **quality** and **freshness** of IOCs is a problem commonly found in Threat Intelligence Platforms. We tried to solve it using a simple yet customizable system.
Upon release, MISP will be shipped with few models that could fit most use-cases. Still, we are eagerly waiting for contributions, fine-tunings or feedbacks from users. This would opens up plenty of opportunities includings improved *Models*' precision, parameters tweaking or even integration of machine learning as a new *Model* algorithm.
@ -144,4 +164,4 @@ Furthermore, we are not done yet! There are already improvements cooking in the
- Integration of ``False Positive`` and ``Expiration`` *Sightings*
- Formula tweakings to provide better control on how to reset the ``base_score`` once a *Sighting* is created
- Per-user Taxonomies' ``numerical_value`` overrides
- Weights on *Tag*'s predicate level
- Weights on *Tag*'s predicate level