Replace packet fields with a regex and display filter. This is useful for removing personally sensitive information by field. TraceWrangler also performs this function, but is limited to a Windows GUI and has a limited set of editable fields.
You can install from regexcap@PyPI with pip.
pip install regexcapAlternatively, you can install by cloning it and installing it with pip.
git clone https://github.com/pocc/regexcap
cd regexcap
pip install .
$ regexcap --help
usage: regexcap [-h] -r R -w W -e E [-s S] -d D [-Y Y] [-m] [-p]
Replace pcap fields with regex
optional arguments:
-h, --help show this help message and exit
-r R input file. Use - for stdin
-w W output file. Use - for stdout
-e E field to change. Multiple fields can be specified like `-e ip.src -e ip.dst`. Replacements will occur on all specified fields. If `frame` is specified, matching frameswill be replaced in their entirety.
-s S source field bytes regex. Defaults to regex ".*" if no arg is provided.
-d D destination field bytes
-Y Y Before replacing bytes, delete packets that do not match this display filter
-m Speed up execution with multiprocessing by using one process per cpu.Output is always pcapng. If source file is a pcapng, then header data will be rewritten recognizing mergecap as the most recent packet writer.
-p Use scapy for packet processing. Currently 50% slower and always saves to pcap.- This replaces bytes in packets, not in packet or pcap headers. Those fields are not accessible to tshark.
- Options
-r,-w,-e, and-Yare copied from tshark for sake of familiarity - Whil the default is to not modify pcap/packet header data, multiprocessing (
-m) modifies and scapy-processing (-p) drops this data. -muses multiprocessing and will speed up execution for large files-Yand-mcreate temporary files that are deleted on exit- Avoid shorthand display filters like
-e ip.addrand use their more explicit representations like-e ip.src -e ip.dst. Tshark maps shorthand display filters to exactly one field in json output, so fewer fields may be replaced than expected. - Currently set to error if there is a length mismatch between old and new values.
- This program will be slow! It uses python with a naive algorithm (i.e. it works)
For example to replace the NIC-specific (last 6 bytes) part of all mac addresses:
$ tshark -r new.pcap -c 1
1 6c:96:cf:d8:7f:e7 → cc:65:ad:da:39:70 108.233.248.45 → 157.245.238.3 ...
$ regexcap -r old.pcap -w new.pcap -e eth.src -e eth.dst -s '.{6}$' -d 000000
$ tshark -r new.pcap -c 1
1 6c:96:cf:00:00:00 → cc:65:ad:00:00:00 108.233.248.45 → 157.245.238.3 ....{6}: Take exactly six bytes of any type$: This regex ends at the end of the field
To replace all private IP addresses with quad 0's, use a byte regex like so:
$ tshark -r new.pcap -c 1
1 0.000000 192.168.1.246 → 217.221.186.35 TCP 54 59793 → https(443) [ACK] Seq=1 Ack=1 Win=2048 Len=0
$ regexcap -r old.pcap -w new.pcap -d '^(?:0a..|ac1.|c0a8).{4}' -s '00000000' -e ip.addr
$ tshark -r new.pcap -c 1
1 0.000000 0.0.0.0 → 217.221.186.35 TCP 54 59793 → https(443) [ACK] Seq=1 Ack=1 Win=2048 Len=0Breaking down the regex, an IP address is 32 bits => 8 nibbles (hexadecimal characters). The network bits of each of the private subnets determines how many nibbles each requires. In other words /8 => 2 network chars, /12 => 3 network chars, /16 => 4 network chars.
^: regex starts at beginning of field(?:...):10.0.0.0/8 =====> 0x0a + ......172.16.0.0/12 ==> 0xac1 + .....192.168.0.0/16 => 0xc0a8 + .....{4}summarizes the last 4 nibbles that are shared
To convert any IP address octet from decimal to hex, you can use the python built-in:
>>> hex(172)
'0xac'Run tests/run_tests or pytest -vvv -x from the root dir.
Apache 2.0
Ross Jacobs, author, rj[AT]swit.sh https://github.com/pocc/regexcap