pDiff - Binary Protocol Differ

This is a simple script to do some basic differential analysis of a pcap and provide insight into unknown protocols.

You can analyze a pcap using a bpf filter, but it is not required.

There are a number of flags you can use to limit or expand your search.

Flag	Description
-p file.pcap	Specify the pcap to analyze
-f "bpf filter"	BPF Filter to use
-m number	The number of most common bytes to list per byte offset
-n	Number of bytes to read for analysis (Default: 30)
-l	Number of packet lengths to count for frequency (Default: 20)
-x	Enable hex mode, view a hex dump of each packet, as well as packet metadata
-a	Turns on printable chars for frequency analysis
-t number	Total number of packets to read (Default: All)
-o	Offset to start at within the packet's payload (Default: 0)

Things to note:

Bytes and offsets are 0 indexed, packets are 1 indexed.
Packets are ignored when they don't meet the minimum length for packet payload (default 2)
Currently only supports TCP and UDP

PRs are welcome! This tool, like many other packet parsing tools, may have some unexpected bugs. Use at your own risk.

Requirements

Read file with filter, in output bytes show printable characters

python3 pDiff.py -p some_random.pcap -f "tcp dst port 1900" -a

Read file with filter, show the output of each packet in hex, only scan 10 packets of the pcap

python3 pDiff.py -p some_random.pcap -f "udp dst port 5555" -x -t 10

Read file without filter, show the output of each packet in hex, start at offset 2 within packet, read 10 bytes

python3 pDiff.py -p some_random.pcap -x -o 2 -n 10

Read file with filter, do statistics on 60 bytes instead of default 30

python3 pDiff.py -p randompcap2.pcap -f "dst net 192.168.1.0/24 && (udp dst port 5555 or udp dst port 9999)" -n 60

Eyeball sequence numbers by observing the frequency of certain bytes and if they look sequential.
Pick out delimiters and possibly padding of certain data types when all the values of a particular byte are the same.

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