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 libpcap-style capture file.
text2pcap can read hexdumps with multiple packets in them, and build a
capture 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 digits. 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 restrictions, 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 character 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 directives 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.
Possiblities include inserting headers such as Ethernet, Ethernet + IP,
Ethernet + IP + UDP, or Ethernet + Ip + TCP 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 1.1.4
Generate a capture file from an ASCII hexdump of packets.
See https://www.wireshark.org for more information.
Usage: text2pcap [options] <infile> <outfile>
where <infile> specifies input filename (use - for standard input)
<outfile> specifies output filename (use - for standard output)
Input:
-o hex|oct|dec parse offsets as (h)ex, (o)ctal or (d)ecimal; default is hex.
-t <timefmt> treats the text before the packet as a date/time code;
the specified argument is a format string of the sort
supported by strptime.
Example: The time "10:15:14.5476" has the format code
"%H:%M:%S."
NOTE: The subsecond component delimiter must be given
(.) but no pattern is required; the remaining number
is assumed to be fractions of a second.
NOTE: Date/time fields from the current date/time are
used as the default for unspecified fields.
Output:
-l <typenum> link-layer type number; default is 1 (Ethernet).
See the file net/bpf.h for list of numbers.
Use this option if your dump is a complete hex dump
of an encapsulated packet and you wish to specify
the exact type of encapsulation.
Example: -l 7 for ARCNet packets.
-m <max-packet> max packet length in output; default is 64000
Prepend dummy header:
-e <l3pid> prepend dummy Ethernet II header with specified L3PID
(in HEX).
Example: -e 0x806 to specify an ARP packet.
-i <proto> prepend dummy IP header with specified IP protocol
(in DECIMAL).
Automatically prepends Ethernet header as well.
Example: -i 46
-u <srcp>,<destp> prepend dummy UDP header with specified
dest and source ports (in DECIMAL).
Automatically prepends Ethernet & IP headers as well.
Example: -u 1000 69 to make the packets look like TFTP/UDP packets.
-T <srcp>,<destp> prepend dummy TCP header with specified
dest and source ports (in DECIMAL).
Automatically prepends Ethernet & IP headers as well.
Example: -T 50,60
-s <srcp>,<dstp>,<tag> prepend dummy SCTP header with specified
dest/source ports and verification tag (in DECIMAL).
Automatically prepends Ethernet & IP headers as well.
Example: -s 30,40,34
-S <srcp>,<dstp>,<ppi> prepend dummy SCTP header with specified
dest/source ports and verification tag 0.
Automatically prepends a dummy SCTP DATA
chunk header with payload protocol identifier ppi.
Example: -S 30,40,34
Miscellaneous:
-h display this help and exit.
-d detailed debug of parser states.
-q generate no output at all (automatically turns off -d).
