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D.8. text2pcap: Converting ASCII hexdumps

to network captures

There may be some occasions when you wish to convert a hex dump of some network traffic into a

libpcap file.

Text2pcap is a program that reads in an ASCII hex dump and writes the data described into a libp-

cap-style capture file. text2pcap can read hexdumps with multiple packets in them, and build a cap-

ture file of multiple packets. text2pcap is also capable of generating dummy Ethernet, IP and UDP

headers, in order to build fully processable packet dumps from hexdumps of application-level data

only.

Text2pcap understands a hexdump of the form generated by od -A x -t x1. In other words, each byte

is individually displayed and surrounded with a space. Each line begins with an offset describing the

position in the file. The offset is a hex number (can also be octal - see -o), of more than two hex di-

gits. Here is a sample dump that text2pcap can recognize:

000000 00 e0 1e a7 05 6f 00 10 ........

000008 5a a0 b9 12 08 00 46 00 ........

000010 03 68 00 00 00 00 0a 2e ........

000018 ee 33 0f 19 08 7f 0f 19 ........

000020 03 80 94 04 00 00 10 01 ........

000028 16 a2 0a 00 03 50 00 0c ........

000030 01 01 0f 19 03 80 11 01 ........

There is no limit on the width or number of bytes per line. Also the text dump at the end of the line

is ignored. Bytes/hex numbers can be uppercase or lowercase. Any text before the offset is ignored,

including email forwarding characters '>'. Any lines of text between the bytestring lines is ignored.

The offsets are used to track the bytes, so offsets must be correct. Any line which has only bytes

without a leading offset is ignored. An offset is recognized as being a hex number longer than two

characters. Any text after the bytes is ignored (e.g. the character dump). Any hex numbers in this

text are also ignored. An offset of zero is indicative of starting a new packet, so a single text file

with a series of hexdumps can be converted into a packet capture with multiple packets. Multiple

packets are read in with timestamps differing by one second each. In general, short of these restric-

tions, text2pcap is pretty liberal about reading in hexdumps and has been tested with a variety of

mangled outputs (including being forwarded through email multiple times, with limited line wrap

etc.)

There are a couple of other special features to note. Any line where the first non-whitespace charac-

ter is '#' will be ignored as a comment. Any line beginning with #TEXT2PCAP is a directive and

options can be inserted after this command to be processed by text2pcap. Currently there are no dir-

ectives implemented; in the future, these may be used to give more fine grained control on the dump

and the way it should be processed e.g. timestamps, encapsulation type etc.

Text2pcap also allows the user to read in dumps of application-level data, by inserting dummy L2,

L3 and L4 headers before each packet. The user can elect to insert Ethernet headers, Ethernet and

IP, or Ethernet, IP and UDP headers before each packet. This allows Wireshark or any other full-

packet decoder to handle these dumps.

Example D.6. Help information available for text2pcap

$ text2pcap -h

Text2pcap 0.99.6

Generate a capture file from an ASCII hexdump of packets.

See http://www.wireshark.org for more information.

Usage: text2pcap [-h] [-d] [-q] [-o h|o] [-l typenum] [-e l3pid] [-i proto]

[-m max-packet] [-u srcp,destp] [-T srcp,destp] [-s srcp,destp,tag]

[-S srcp,destp,tag] [-t timefmt] <input-filename> <output-filename>

where <input-filename> specifies input filename (use - for standard input)

Related command line tools

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