openssl-asn1parse, asn1parse - ASN.1 parsing tool
openssl asn1parse [-help] [-inform
PEM|DER] [-in filename] [-out filename] [-noout]
[-offset number] [-length number] [-i] [-oid
filename] [-dump] [-dlimit num] [-strparse offset]
[-genstr string] [-genconf file] [-strictpem] [-item
The asn1parse command is a diagnostic utility that can
parse ASN.1 structures. It can also be used to extract data from ASN.1
- Print out a usage message.
- 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.
- Don't output the parsed version of the input file.
- Starting offset to begin parsing, default is start of file.
- Number of bytes to parse, default is until end of file.
- Indents the output according to the "depth" of the
- -oid filename
- A file containing additional OBJECT IDENTIFIERs (OIDs). The format of this
file is described in the NOTES section below.
- Dump unknown data in hex format.
- Like -dump, but only the first num bytes are output.
- Parse the contents octets of the ASN.1 object starting at offset.
This option can be used multiple times to "drill down" into a
- -genstr string,
- 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.
- If this option is used then -inform will be ignored. Without this
option any data in a PEM format input file will be treated as being base64
encoded and processed whether it has the normal PEM BEGIN and END markers
or not. This option will ignore any data prior to the start of the BEGIN
marker, or after an END marker in a PEM file.
- -item name
- Attempt to decode and print the data as ASN1_ITEM name. This can be
used to print out the fields of any supported ASN.1 structure if the type
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. 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
Some knowledge of the ASN.1 structure is needed to interpret the
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
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
If an OID is not part of OpenSSL's internal table it will be
represented in numerical form (for example 22.214.171.124). 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:
"126.96.36.199 shortName A long
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
openssl asn1parse -genstr 'UTF8:Hello World' -noout -out utf8.der
Generate using a config file:
openssl asn1parse -genconf asn1.cnf -noout -out asn1.der
Example config file:
field2=EXP:0, UTF8:some random string
There should be options to change the format of output lines. The
output of some ASN.1 types is not well handled (if at all).
Copyright 2000-2017 The OpenSSL Project Authors. All Rights
Licensed under the OpenSSL license (the "License"). You
may not use this file except in compliance with the License. You can obtain
a copy in the file LICENSE in the source distribution or at