dumpder.go

dumpDER.go - dump a DER file, displaying its structure and content

Description

dumpDER is an example of using the encoding/asn1 package to read and parse a DER file from stdin. It will display the DER file structure on stdout as well as the data it included, trying to improve the information displayed by converting the most current types (time, string, etc.) in a readable way and retrieving the name of object identifiers from the object identifier repository.

Build

Make sure both files dumpDER.go and object_name.go are in the same empty directory, and use the go build command to build the dumpDER executable.

Usage

Use the dumpDER command providing a DER file as its standard input. Example :

dumpDER < file.der

I tried it with smime.p7s files, as well as cert, request and keypair files. I took my test files from X509 certificate examples for testing and verification

$ ./dumpDER </512b-rsa-example-request.der
Note: all INTEGER, OCTET STRING and BIT STRING values displayed as hexadecimal bytes
SEQUENCE (260 bytes)                            :
| SEQUENCE (175 bytes)                          :
| | INTEGER (1 bytes)                           : 00
| | SEQUENCE (74 bytes)                         :
| | | SET (11 bytes)                            :
| | | | SEQUENCE (9 bytes)                      :
| | | | | OBJECT IDENTIFIER (3 bytes)           : 2.5.4.6 attributeType(4) countryName(6)
| | | | | PRINTABLE STRING (2 bytes)            : JP
| | | SET (14 bytes)                            :
| | | | SEQUENCE (12 bytes)                     :
| | | | | OBJECT IDENTIFIER (3 bytes)           : 2.5.4.8 attributeType(4) stateOrProvinceName(8)
| | | | | UTF8 STRING (5 bytes)                 : Tokyo
| | | SET (17 bytes)                            :
| | | | SEQUENCE (15 bytes)                     :
| | | | | OBJECT IDENTIFIER (3 bytes)           : 2.5.4.10 attributeType(4) organizationName(10)
| | | | | UTF8 STRING (8 bytes)                 : Frank4DD
| | | SET (24 bytes)                            :
| | | | SEQUENCE (22 bytes)                     :
| | | | | OBJECT IDENTIFIER (3 bytes)           : 2.5.4.3 attributeType(4) commonName(3)
| | | | | UTF8 STRING (15 bytes)                : www.example.com
| | SEQUENCE (92 bytes)                         :
| | | SEQUENCE (13 bytes)                       :
| | | | OBJECT IDENTIFIER (9 bytes)             : 1.2.840.113549.1.1.1 pkcs-1(1) rsaEncryption(1)
| | | | NULL (0 bytes)                          : NUL
| | | BIT STRING (75 bytes)                     : 00 30 48 02 41 00 9B FC 66 90 79 84 42 BB AB 13
| | | |                                           FD 2B 7B F8 DE 15 12 E5 F1 93 E3 06 8A 7B B8 B1
| | | |                                           E1 9E 26 BB 95 01 BF E7 30 ED 64 85 02 DD 15 69
| | | |                                           A8 34 B0 06 EC 3F 35 3C 1E 1B 2B 8F FA 8F 00 1B
| | | |                                           DF 07 C6 AC 53 07 02 03 01 00 01
| | 0 (0 bytes)                                 :
| SEQUENCE (13 bytes)                           :
| | OBJECT IDENTIFIER (9 bytes)                 : 1.2.840.113549.1.1.5 pkcs-1(1) sha1-with-rsa-signature(5)
| | NULL (0 bytes)                              : NUL
| BIT STRING (65 bytes)                         : 00 72 39 5E 76 63 5E F2 F3 1C 35 57 FC 6F AE ED
| |                                               EB 2C FA D5 C5 80 17 4B 94 A0 BC DA 5F 06 C8 F7
| |                                               F2 53 55 B5 3B EE 1F F3 20 AE 80 60 9A 34 A9 9E
| |                                               A2 AA 06 20 43 92 86 36 61 41 13 DA A9 86 8C 0B
| |                                               BD

Known limitations

1. The encoding/asn1package only implements a subset of ASN.1. Not all ASN.1 types are recognized. The list of the ASN.1 types than can be recognized by the encoding/asn1 package are described in the Unmarshal function documentation
2. To retrieve the name of an ASN.1 object identifier, I am using a GET from the OID Repository Web site. It's not very efficient, especially for DER file with a lot of objects, and should be optimized ➔ this is now fixed: dumpDER.gp manages a map of object identifiers names. It now knows the most often used objects identifiers and their names. When a new objectif identifier is found, its name is added to the map to avoid multiple requests to oid-info.com
3. Some objects use OCTET STRING or BIT STRING as extension for other ASN.1 data, as described here. These extensions are currently not parsed as ASN.1 data and only displayed as hexadecimal bytes ➔ as a partial fix, dumpDER now tries to parse OCTET STRING and BIT STRING that start like a SEQUENCE