ASN1PARSE(1) OpenSSL ASN1PARSE(1) NNAAMMEE openssl-asn1parse, asn1parse - ASN.1 parsing tool SSYYNNOOPPSSIISS ooppeennssssll aassnn11ppaarrssee [--iinnffoorrmm PPEEMM||DDEERR] [--iinn ffiilleennaammee] [--oouutt ffiilleennaammee] [--nnoooouutt] [--ooffffsseett nnuummbbeerr] [--lleennggtthh nnuummbbeerr] [--ii] [--ooiidd ffiilleennaammee] [--dduummpp] [--ddlliimmiitt nnuumm] [--ssttrrppaarrssee ooffffsseett] [--ggeennssttrr ssttrriinngg] [--ggeennccoonnff ffiillee] DDEESSCCRRIIPPTTIIOONN The aassnn11ppaarrssee command is a diagnostic utility that can parse ASN.1 structures. It can also be used to extract data from ASN.1 formatted data. OOPPTTIIOONNSS --iinnffoorrmm DDEERR||PPEEMM the input format. DDEERR is binary format and PPEEMM (the default) is base64 encoded. --iinn ffiilleennaammee the input file, default is standard input --oouutt ffiilleennaammee 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 --ssttrrppaarrssee option. --nnoooouutt don't output the parsed version of the input file. --ooffffsseett nnuummbbeerr starting offset to begin parsing, default is start of file. --lleennggtthh nnuummbbeerr number of bytes to parse, default is until end of file. --ii indents the output according to the "depth" of the structures. --ooiidd ffiilleennaammee a file containing additional OBJECT IDENTIFIERs (OIDs). The format of this file is described in the NOTES section below. --dduummpp dump unknown data in hex format. --ddlliimmiitt nnuumm like --dduummpp, but only the first nnuumm bytes are output. --ssttrrppaarrssee ooffffsseett parse the contents octets of the ASN.1 object starting at ooffffsseett. This option can be used multiple times to "drill down" into a nested structure. --ggeennssttrr ssttrriinngg, --ggeennccoonnff ffiillee generate encoded data based on ssttrriinngg, ffiillee or both using _A_S_N_1___g_e_n_- _e_r_a_t_e___n_c_o_n_f(3) format. If ffiillee only is present then the string is obtained from the default section using the name aassnn11. 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 oouutt option. OOUUTTPPUUTT 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. dd==XXXX specifies the current depth. The depth is increased within the scope of any SET or SEQUENCE. hhll==XXXX gives the header length (tag and length octets) of the current type. ll==XXXX gives the length of the contents octets. The --ii option can be used to make the output more readable. Some knowledge of the ASN.1 structure is needed to interpret the out- put. In this example the BIT STRING at offset 229 is the certificate public key. The contents octets of this will contain the public key informa- tion. This can be examined using the option --ssttrrppaarrssee 222299 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 NNOOTTEESS If an OID is not part of OpenSSL's internal table it will be repre- sented in numerical form (for example 1.2.3.4). The file passed to the --ooiidd 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". aassnn11ppaarrssee displays the long name. Example: "1.2.3.4 shortName A long name" EEXXAAMMPPLLEESS 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 BBUUGGSS There should be options to change the format of output lines. The out- put of some ASN.1 types is not well handled (if at all). SSEEEE AALLSSOO _A_S_N_1___g_e_n_e_r_a_t_e___n_c_o_n_f(3) 1.0.2u 2019-12-20 ASN1PARSE(1)