From: Brian Candler <B.Candler@...>
Date: 2005-04-08T06:14:16+09:00
Subject: Re: Ruby ASN1 examples?

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On Sat, Mar 26, 2005 at 11:35:07AM +0000, Brian Candler wrote:
> Does anyone have any example code I can see for dealing with ASN1 in Ruby?

I finally hacked my way through this, and am posting it here for reference.

The hardest part was how to make a tagged instance of a tagged type. That
is, in the example in Annex A of X.690, we have:

    dateOfHire    [1] Date,
...
    Date ::= [APPLICATION 3] IMPLICIT VisibleString    -- YYYYMMDD

So we have Date as a tagged type, and dateOfHire as a tagged instance of
that type.

The Annex shows that this encodes as:

  dateOfHire  Length
      A1        0A     <----------------------->
                        Date  Length  Contents
                         43     08   "19710917"

It's easy to generate an untagged instance of the Date type, like this:

  date = OpenSSL::ASN1::ISO64String("19710917", 3, :IMPLICIT, :APPLICATION)
  p date.to_der   # => 43 08 "19710917"

And it's also easy to generate a tagged instance of a universal type:

  foo = OpenSSL::ASN1::ISO64String("19710917", 1, :EXPLICIT, :CONTEXT_SPECIFIC)
  p foo.to_der    # => A1 0A 1A 08 "19710917"
                             ^
                             `-- VisibleString (not Date)

But a tagged instance of a tagged type is tricky. The only way I could
figure out was:

  date = OpenSSL::ASN1::ISO64String("19710917", 3, :IMPLICIT, :APPLICATION)
  date2 = OpenSSL::ASN1::ASN1Data.new([date], 1, :CONTEXT_SPECIFIC)
  p date2.to_der  # => A1 0A 43 08 "19710917"

ext/openssl/ossl_asn1.c claims to be written by "'OpenSSL for Ruby' team
members" - are there any of them here who would care to comment? Is there an
easier way to achieve this?

Regards,

Brian.

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require 'openssl'
require 'test/unit'

# This is a test which replicates the test case in Annex A of ITU-T Rec. X.690
# See http://www.itu.int/ITU-T/studygroups/com17/languages/X.690-0207.pdf

class TestASN < Test::Unit::TestCase

  def test_john_p_smith
    a = OpenSSL::ASN1::Set([], 0, :IMPLICIT, :APPLICATION)
    name = OpenSSL::ASN1::Sequence([], 1, :IMPLICIT, :APPLICATION)
      name.value << OpenSSL::ASN1::ISO64String("John")
      name.value << OpenSSL::ASN1::ISO64String("P")
      name.value << OpenSSL::ASN1::ISO64String("Smith")
    a.value << name
    a.value << OpenSSL::ASN1::ISO64String("Director", 0, :EXPLICIT, :CONTEXT_SPECIFIC)
    a.value << OpenSSL::ASN1::Integer(51, 2, :IMPLICIT, :APPLICATION)
    x = OpenSSL::ASN1::ISO64String("19710917", 3, :IMPLICIT, :APPLICATION)
    date = OpenSSL::ASN1::ASN1Data.new([x], 1, :CONTEXT_SPECIFIC)
    a.value << date

    x = OpenSSL::ASN1::Sequence([], 1, :IMPLICIT, :APPLICATION)
      x.value << OpenSSL::ASN1::ISO64String("Mary")
      x.value << OpenSSL::ASN1::ISO64String("T")
      x.value << OpenSSL::ASN1::ISO64String("Smith")
    spouse = OpenSSL::ASN1::ASN1Data.new([x], 2, :CONTEXT_SPECIFIC)
    a.value << spouse

    children = OpenSSL::ASN1::Sequence([], 3, :IMPLICIT, :CONTEXT_SPECIFIC)
      child = OpenSSL::ASN1::Set([])
        childname = OpenSSL::ASN1::Sequence([], 1, :IMPLICIT, :APPLICATION)
          childname.value << OpenSSL::ASN1::ISO64String("Ralph")
          childname.value << OpenSSL::ASN1::ISO64String("T")
          childname.value << OpenSSL::ASN1::ISO64String("Smith")
        child.value << childname
        x = OpenSSL::ASN1::ISO64String("19571111", 3, :IMPLICIT, :APPLICATION)
        childdob = OpenSSL::ASN1::ASN1Data.new([x], 1, :CONTEXT_SPECIFIC)
        child.value << childdob
      children.value << child
      child = OpenSSL::ASN1::Set([])
        childname = OpenSSL::ASN1::Sequence([], 1, :IMPLICIT, :APPLICATION)
          childname.value << OpenSSL::ASN1::ISO64String("Susan")
          childname.value << OpenSSL::ASN1::ISO64String("B")
          childname.value << OpenSSL::ASN1::ISO64String("Jones")
        child.value << childname
        x = OpenSSL::ASN1::ISO64String("19590717", 3, :IMPLICIT, :APPLICATION)
        childdob = OpenSSL::ASN1::ASN1Data.new([x], 1, :CONTEXT_SPECIFIC)
        child.value << childdob
      children.value << child
    a.value << children

    der = a.to_der
    bytes = der.unpack("H*")[0].scan(/(..)/).join(":")
    p bytes

    decode = OpenSSL::ASN1.decode(der)
    # decode != a because some source ASN1::Set or Sequence become
    # ASN1Data in the output, as do our application-defined types
    require 'pp'
    pp a
    pp decode
  end
end

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