NAME¶
asn1parse - ASN.1 parsing tool
SYNOPSIS¶
openssl asn1parse [
-inform PEM|DER] [
-in filename]
[
-out filename] [
-noout] [
-offset number] [
-length
number] [
-i] [
-oid filename] [
-dump] [
-dlimit
num] [
-strparse offset] [
-genstr string] [
-genconf
file]
DESCRIPTION¶
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¶
- -inform DER|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.
- -dump
- dump unknown data in hex format.
- -dlimit num
- like -dump, but only the first num bytes are output.
- -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:
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
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
-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:
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
BUGS¶
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).
SEE ALSO¶
ASN1_generate_nconf(3)