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README.md

Grizzly BER

This library implements a TLV-BER parser, used for processing EMV transaction-related data.

This works differently from OpenSSL::ASN1 in that it does not decode tags (EMV-style). This is important when processing a long tag like 9F02 (Amount Authorized in EMV). OpenSSL will write it as the TLV-DER tag 82. GrizzlyBer maintains the original TLV-BER tag 9F02.

tlv_string = "9F0206000000000612"
 => "9F0206000000000612" 

OpenSSL::ASN1.decode([tlv_string].pack("H*")).to_der.unpack("H*").first.upcase
 => "8206000000000612" 

GrizzlyBer.new(tlv_string).to_ber
 => "9F0206000000000612" 

Installation

Add this line to your application's Gemfile:

gem 'grizzly_ber'

And then execute:

$ bundle

Or install it yourself as:

$ gem install grizzly_ber

Usage

Instantiate a TLV instance with a TLV-BER-encoded hex string to decode it

tlv = GrizzlyBer.new("DFAE22015A")

Access a value by tag

tlv = GrizzlyBer.new
tlv["DFAE22"] #returns [0x5A]

Set a value by tag

tlv = GrizzlyBer.new
tlv.tag = 0xDFAE22
tlv["DFAE22"] = [0xAA]
tlv.set_hex_value_for_tag("DFAE22", "AA")

Create multi-dimensional structures

tlv = GrizzlyBer.new
tlv["E1"] = GrizzlyBer.new
tlv["E1"]["5A"] = [0xaa, 0x12, 0x34]
tlv["E1"].set_hex_value_for_tag("57", "55A55A")

Encode the TLV instance back out to a hex string

tlv = GrizzlyBer.new("DFAE22015A")
hex_string = tlv.to_ber

Access EMV-specific values by name

tlv = GrizzlyBer.new
tlv["8A"] = [0x30, 0x30]
tlv["Authorisation Response Code"] = [0x30, 0x30]

Pretty-print EMV-specific data

puts GrizzlyBer.new "500B5649534120435245444954"
#50: Application Label
# Description: Mnemonic associated with the AID according to ISO/IEC 7816-5
# Value: 5649534120435245444954, "VISA CREDIT"

Contributing

  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Added some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request

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GrizzlyBer, the fiercest TLV-BER parser!

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