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.
-genstr string, -genconf file
generate encoded data based on string, file or both using ASN1_generate_nconf(3)
format. If file only is
present then the string is obtained from the default section
using the name asn1. The
encoded data is passed through the ASN1 parser and printed
out as though it came from a file, the contents can thus be
examined and written to a file using the out option.
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:
1.2.3.4 shortName A long
name
EXAMPLES
Parse a file:
openssl asn1parse -in file.pem
Parse a DER file:
openssl asn1parse -inform DER -in file.der
Generate a simple UTF8String:
openssl asn1parse -genstr 'UTF8:Hello World'
Generate and write out a UTF8String, don't print parsed output:
