Rasn1

Rasn1 is a ruby ASN.1 library to encode, parse and decode ASN.1 data in DER format.

Installation

Add this line to your application's Gemfile:

gem 'rasn1'

And then execute:

bundle install

Or install it yourself as:

gem install rasn1

Simple usage

To decode a DER/BER string without checking a model, do:

decoded_der = RASN1.parse(der_string)
decoded_ber = RASN1.parse(ber_string, ber: true)

Advanced usage

All examples below will be based on:

Record ::= SEQUENCE {
  id        INTEGER,
  room  [0] INTEGER OPTIONAL,
  house [1] INTEGER DEFAULT 0
}

ComplexRecord ::= SEQUENCE {
  bool      BOOLEAN,
  data  [0] EXPLICIT OCTET STRING,
  a_record  Record
}

Create an ASN.1 model

A model is created this way:

class Record < RASN1::Model
  sequence :record,
           content: [integer(:id),
                     integer(:room, implicit: 0, optional: true),
                     integer(:house, implicit: 1, default: 0)]
end

or, this ways in a more rubyish style:

# This Record class is defined as a sequence conaining:
# * an ID (integer)
# * a room number (integer, with explicit tag, optional)
# * a house if (integer, with explicit tag and a default value)
class Record < RASN1::Model
  sequence :record do
    integer(:id)
    integer(:room, implicit: 0, optional: true)
    integer(:house, implicit: 1, default: 0)
  end
end

More comple classes may be designed by nesting simple classes. For example:

class ComplexRecord < RASN1::Model
  sequence :cplx_record do
    boolean(:bool)
    octet_string(:data, explicit: 0)
    model(:a_record, Record)          # Use another model in model
  end
end

Parse a DER-encoded string

record = Record.parse(der_string)
record[:id]             # => RASN1::Types::Integer
record[:id].value       # => Integer
record[:id].to_i        # => Integer
record[:id].asn1_class  # => Symbol
record[:id].optional?   # => false
record[:id].default     # => nil
record[:room].optional  # => true
record[:house].default  # => 0

record[:id].to_der      # => String

cplx_record = ComplexRecord.parse(der_string)
cplx_record[:bool]            # => RASN1::Types::Boolean
cplx_record[:bool].value      # => TrueClass/FalseClass
cplx_record[:data].value      # => String
cplx_record[:data].explicit?  # => true
cplx_record[:a_record]        # => Record

Generate a DER-encoded string

record = Record.new(id: 12)
record[:id].to_i      # => 12
record[:room]         # => nil
record[:house]        # => 0

# Set one value
record[:room] = 43
record[:room]         # => 43

# Set mulitple values
record.set id: 124, house: 155

record.to_der         # => String

Contributing

Bug reports and pull requests are welcome on GitHub at https://codeberg.org/lemontree55/rasn1.