openssl/doc/apps/asn1parse.pod

=pod

=head1 NAME

asn1parse - ASN.1 parsing tool

=head1 SYNOPSIS

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

=head1 DESCRIPTION

The B<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.

=head1 OPTIONS

=over 4

=item B<-inform> B<DER|PEM>

the input format. B<DER> is binary format and B<PEM> (the default) is base64
encoded.

=item B<-in filename>

the input file, default is standard input

=item B<-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 B<-strparse> option.

=item B<-noout>

don't output the parsed version of the input file.

=item B<-offset number>

starting offset to begin parsing, default is start of file.

=item B<-length number>

number of bytes to parse, default is until end of file.

=item B<-i>

indents the output according to the "depth" of the structures.

=item B<-oid filename>

a file containing additional OBJECT IDENTIFIERs (OIDs). The format of this
file is described in the NOTES section below.

=item B<-strparse offset>

parse the contents octets of the ASN.1 object starting at B<offset>. This
option can be used multiple times to "drill down" into a nested structure.


=back

=head2 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 the
offset in decimal. B<d=XX> specifies the current depth. The depth is increased
within the scope of any SET or SEQUENCE. B<hl=XX> gives the header length
(tag and length octets) of the current type. B<l=XX> gives the length of
the contents octets.

The B<-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 B<-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

=head1 NOTES

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 B<-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". B<asn1parse> displays the long name. Example:

C<1.2.3.4	shortName	A long name>

=head1 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).

=cut