The asn1parse command is a diagnostic utility that can parse ASN.1
structures. It can also be used to extract data from ASN.1 formatted data.
OPTIONS
-informDER|PEM
the input format. DER is binary format and PEM (the default) is base64
encoded.
-in filename
the input file, default is standard input
-out filename
output file to place the DER encoded data into. If this
option is not present then no data will be output. This is most useful when
combined with the -strparse option.
-noout
don't output the parsed version of the input file.
-offset number
starting offset to begin parsing, default is start of file.
-length number
number of bytes to parse, default is until end of file.
-i
indents the output according to the ``depth'' of the structures.
-oid filename
a file containing additional OBJECT IDENTIFIERs (OIDs). The format of this
file is described in the NOTES section below.
-strparse offset
parse the contents octets of the ASN.1 object starting at offset. This
option can be used multiple times to ``drill down'' into a nested structure.
OUTPUT
The output will typically contain lines like this:
This example is part of a self signed certificate. Each line starts with the
offset in decimal. d=XX specifies the current depth. The depth is increased
within the scope of any SET or SEQUENCE. hl=XX gives the header length
(tag and length octets) of the current type. l=XX gives the length of
the contents octets.
The -i option can be used to make the output more readable.
Some knowledge of the ASN.1 structure is needed to interpret the output.
In this example the BIT STRING at offset 229 is the certificate public key.
The contents octets of this will contain the public key information. This can
be examined using the option -strparse 229 to yield:
If an OID is not part of OpenSSL's internal table it will be represented in
numerical form (for example 1.2.3.4). The file passed to the -oid option
allows additional OIDs to be included. Each line consists of three columns,
the first column is the OID in numerical format and should be followed by white
space. The second column is the ``short name'' which is a single word followed
by white space. The final column is the rest of the line and is the
``long name''. asn1parse displays the long name. Example:
1.2.3.4shortNameA long name
BUGS
There should be options to change the format of input lines. The output of some
ASN.1 types is not well handled (if at all).