-help

Print out a usage message.

-inform

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

-in

the input file, default is standard input

-out

output file to place the DER encoded data into. If this option is not present then no data will be output. This is most usefulwhen combined with the -strparse option.

-noout

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

-offset

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

-length

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

-i

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

-oid

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.

-dlimit

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

-strparse

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

-genstr

generate encoded data based on string, file or both using ASN1_generate_nconf(3) format. If file only is present then the stringis obtained from the default section using the name asn1. The encoded data is passed through the ASN1 parser and printed out asthough 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 asbeing base64 encoded and processed whether it has the normal PEM BEGIN and END markers or not. This option will ignore any dataprior to the start of the BEGIN marker, or after an END marker in a PEM file.OutputThe 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 STRING373:d=2 hl=3 l= 162 cons: cont [ 3 ]376:d=3 hl=3 l= 159 cons: SEQUENCE379:d=4 hl=2 l= 29 cons: SEQUENCE381:d=5 hl=2 l= 3 prim: OBJECT :X509v3 Subject Key Identifier386:d=5 hl=2 l= 22 prim: OCTET STRING410:d=4 hl=2 l= 112 cons: SEQUENCE412:d=5 hl=2 l= 3 prim: OBJECT :X509v3 Authority Key Identifier417:d=5 hl=2 l= 105 prim: OCTET STRING524: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. Thedepth is increased within the scope of any SET or SEQUENCE. hl=XX gives the header length (tag and length octets) of the currenttype. 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 keyinformation. This can be examined using the option -strparse 229 to yield:0:d=0 hl=3 l= 137 cons: SEQUENCE3:d=1 hl=3 l= 129 prim: INTEGER :E5D21E1F5C8D208EA7A2166C7FAF9F6BDF2059669C60876DDB70840F1A5AAFA59699FE471F379F1DD6A487E7D5409AB6A88D4A9746E24B91D8CF55DB3521015460C8EDE44EE8A4189F7A7BE77D6CD3A9AF2696F486855CF58BF0EDF2B4068058C7A947F52548DDF7E15E96B385F86422BEA9064A3EE9E1158A56E4A6F47E5897135:d=1 hl=2 l= 3 prim: INTEGER :010001NOTESIf 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 tothe -oid option allows additional OIDs to be included. Each line consists of three columns, the first column is the OID in numericalformat 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"EXAMPLESParse a file:openssl asn1parse -in file.pemParse a DER file:openssl asn1parse -inform DER -in file.derGenerate 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.derGenerate using a config file:openssl asn1parse -genconf asn1.cnf -noout -out asn1.derExample config file:asn1=SEQUENCE:seq_sect[seq_sect]field1=BOOL:TRUEfield2=EXP:0, UTF8:some random stringBUGSThere should be options to change the format of output lines. The output of some ASN.1 types is not well handled (if at all).