openssl-asn1parse - ASN.1 parsing command

       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 2000-2023 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (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
       <https://www.openssl.org/source/license.html>.

3.4.1                                              2025-04-03                            OPENSSL-ASN1PARSE(1SSL)

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

       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:

        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:

        asn1=SEQUENCE:seq_sect

        [seq_sect]

        field1=BOOL:TRUE
        field2=EXP:0, UTF8:some random string

       openssl-asn1parse - ASN.1 parsing command

       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 whitespace. The final column is  the
       rest of the line and is the "long name". Example:

       "1.2.3.4       shortName       A long name"

       For any OID with an associated short and long name, this command will display the long name.

-help
           Print out a usage message.

       -informDER|PEM|B64
           The input format; the default is PEM.  See openssl-format-options(1) for details.

       -infilename
           The input file, default is standard input.

       -outfilename
           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.

       -offsetnumber
           Starting offset to begin parsing, default is start of file.

       -lengthnumber
           Number of bytes to parse, default is until end of file.

       -i  Indents the output according to the "depth" of the structures.

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

       -dump
           Dump unknown data in hex format.

       -dlimitnum
           Like -dump, but only the first num bytes are output.

       -strparseoffset
           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.

       -genstrstring, -genconffile
           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.

       -strictpem
           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.

       -itemname
           Attempt to decode and print the data as an ASN1_ITEMname. This can be used to print out  the  fields
           of any supported ASN.1 structure if the type is known.

   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. "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:

           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

openssl(1), ASN1_generate_nconf(3)

opensslasn1parse [-help] [-informDER|PEM|B64] [-infilename] [-outfilename] [-noout] [-offsetnumber]
       [-lengthnumber] [-i] [-oidfilename] [-dump] [-dlimitnum] [-strparseoffset] [-genstrstring] [-genconffile] [-strictpem] [-itemname]