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ASN1PARSE

Section: OpenSSL (1)
Updated: 2004-11-26
Index

NAME

asn1parse - ASN.1 parsing tool

SYNOPSIS

openssl asn1parse[-inform PEM|DER][-in filename][-out filename][-noout][-offset number][-length number][-i][-oid filename][-strparse offset]

DESCRIPTION

The asn1parse command is a diagnostic utility that can parse ASN.1structures. It can also be used to extract data from ASN.1 formatted data.

OPTIONS

-inform DER|PEM: the input format. DER is binary format and PEM (the default) is base64encoded.
-in filename: the input file, default is standard input
-out filename: output file to place the DER encoded data into. If thisoption is not present then no data will be output. This is most useful whencombined 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 thisfile is described in the NOTES section below.
-strparse offset: parse the contents octets of the ASN.1 object starting at offset. Thisoption can be used multiple times to ``drill down'' into a nested structure.

OUTPUT

The output will typically contain lines like this:

  0:d=0  hl=4 l= 681 cons: SEQUENCE

.....

  229:d=3  hl=3 l= 141 prim: BIT STRING          373:d=2  hl=3 l= 162 cons: cont [ 3 ]          376:d=3  hl=3 l= 159 cons: SEQUENCE            379:d=4  hl=2 l=  29 cons: SEQUENCE            381:d=5  hl=2 l=   3 prim: OBJECT            :X509v3 Subject Key Identifier  386:d=5  hl=2 l=  22 prim: OCTET STRING        410:d=4  hl=2 l= 112 cons: SEQUENCE            412:d=5  hl=2 l=   3 prim: OBJECT            :X509v3 Authority Key Identifier  417:d=5  hl=2 l= 105 prim: OCTET STRING        524:d=4  hl=2 l=  12 cons: SEQUENCE

.....

This example is part of a self signed certificate. Each line starts with theoffset in decimal. d=XX specifies the current depth. The depth is increasedwithin 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 ofthe 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 canbe examined using the option -strparse 229 to yield:

    0:d=0  hl=3 l= 137 cons: SEQUENCE              3:d=1  hl=3 l= 129 prim: INTEGER           :E5D21E1F5C8D208EA7A2166C7FAF9F6BDF2059669C60876DDB70840F1A5AAFA59699FE471F379F1DD6A487E7D5409AB6A88D4A9746E24B91D8CF55DB3521015460C8EDE44EE8A4189F7A7BE77D6CD3A9AF2696F486855CF58BF0EDF2B4068058C7A947F52548DDF7E15E96B385F86422BEA9064A3EE9E1158A56E4A6F47E5897  135:d=1  hl=2 l=   3 prim: INTEGER           :010001

NOTES

If an OID is not part of OpenSSL's internal table it will be represented innumerical 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 whitespace. The second column is the ``short name'' which is a single word followedby white space. The final column is the rest of the line and is the``long name''. asn1parse displays the long name. Example:

"1.2.3.4 shortName A long name"

BUGS

There should be options to change the format of output lines. The output of someASN.1 types is not well handled (if at all).

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