Entropy

The entropy module calculates the entropy of field values over time. Specifying entropy without any arguments will generate the entropy of all entries DATA fields across the search range. The entropy module supports temporal search mode allowing for charting of entropy over time. entropy can also operate on enumerated values and group by enumerated values. Output values are between 0 and 1.

Syntax:

entropy [enumerated value] [by ...] [over <duration>]

The entropy module syntax allows for specifying an enumerated value to calculate entropy over. If not specified, entropy will calculate entropy over the entire DATA field. The module also supports specifying one or more arguments to group by, using the by keyword. For example, to calcaulte entropy on the enumerated value foo, grouped by bar and baz:

tag=gravwell entropy foo by bar baz

Queries can be temporally grouped over arbitrary time windows using the over keyword:

tag=gravwell entropy over 10m

All arguments are optional.

Supported Options

entropy has no flags.

Examples

This query calculates and charts the entropy of TCP packet payloads based on port:

tag=pcap packet tcp.Port tcp.Payload | entropy Payload by Port | chart entropy by Port

An example query which calculates the entropy of URLS by host and sorts the list based on highest entropy value:

tag=pcap packet tcp.Port==80 ipv4.IP !~ 10.0.0.0/8 tcp.Payload | grep -e Payload GET PUT HEAD POST | regex -e Payload "[A-Z]+\s(?P<url>\S+)\sHTTP\/" | entropy url by IP | table IP entropy