Initial commit

.formatter.exs

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+# Used by "mix format"
+[
+  inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
+]

.gitignore

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+# The directory Mix will write compiled artifacts to.
+/_build/
+
+# If you run "mix test --cover", coverage assets end up here.
+/cover/
+
+# The directory Mix downloads your dependencies sources to.
+/deps/
+
+# Where 3rd-party dependencies like ExDoc output generated docs.
+/doc/
+
+# Ignore .fetch files in case you like to edit your project deps locally.
+/.fetch
+
+# If the VM crashes, it generates a dump, let's ignore it too.
+erl_crash.dump
+
+# Also ignore archive artifacts (built via "mix archive.build").
+*.ez
+
+# Ignore package tarball (built via "mix hex.build").
+atecc508a-*.tar
+

README.md

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+# Atecc508a
+
+**TODO: Add description**
+
+## Installation
+
+If [available in Hex](https://hex.pm/docs/publish), the package can be installed
+by adding `atecc508a` to your list of dependencies in `mix.exs`:
+
+```elixir
+def deps do
+  [
+    {:atecc508a, "~> 0.1.0"}
+  ]
+end
+```
+
+Documentation can be generated with [ExDoc](https://github.com/elixir-lang/ex_doc)
+and published on [HexDocs](https://hexdocs.pm). Once published, the docs can
+be found at [https://hexdocs.pm/atecc508a](https://hexdocs.pm/atecc508a).
+

config/config.exs

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+# This file is responsible for configuring your application
+# and its dependencies with the aid of the Mix.Config module.
+use Mix.Config
+
+# This configuration is loaded before any dependency and is restricted
+# to this project. If another project depends on this project, this
+# file won't be loaded nor affect the parent project. For this reason,
+# if you want to provide default values for your application for
+# 3rd-party users, it should be done in your "mix.exs" file.
+
+# You can configure your application as:
+#
+#     config :atecc508a, key: :value
+#
+# and access this configuration in your application as:
+#
+#     Application.get_env(:atecc508a, :key)
+#
+# You can also configure a 3rd-party app:
+#
+#     config :logger, level: :info
+#
+
+# It is also possible to import configuration files, relative to this
+# directory. For example, you can emulate configuration per environment
+# by uncommenting the line below and defining dev.exs, test.exs and such.
+# Configuration from the imported file will override the ones defined
+# here (which is why it is important to import them last).
+#
+#     import_config "#{Mix.env()}.exs"

lib/atecc508a.ex

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+defmodule ATECC508A do
+  @moduledoc """
+  Documentation for Atecc508a.
+  """
+
+  @doc """
+  Hello world.
+
+
+  """
+
+  @spec decode(<<_::24>>) :: {DateTime.t(), DateTime.t()}
+  def decode(<<raw_year::5, month::4, day::5, hour::5, expire_years::5>>) do
+    issue_date = %DateTime{
+      year: raw_year + 2000,
+      month: month,
+      day: day,
+      hour: hour,
+      minute: 0,
+      second: 0,
+      microsecond: {0, 0},
+      std_offset: 0,
+      utc_offset: 0,
+      zone_abbr: "UTC",
+      time_zone: "Etc/UTC"
+    }
+
+    expire_date =
+      if expire_years != 0 do
+        %DateTime{issue_date | year: issue_date.year + expire_years}
+      else
+        # Special "no expiration date"
+        max_date()
+      end
+
+    {issue_date, expire_date}
+  end
+
+  @spec encode(DateTime.t(), DateTime.t()) :: <<_::24>>
+  def encode(issue_date, expire_date) do
+    expire_years = calc_expire_years(issue_date, expire_date)
+    issue_year = calc_issue_year(issue_date.year)
+
+    <<issue_year::5, issue_date.month::4, issue_date.day::5, issue_date.hour::5, expire_years::5>>
+  end
+
+  defp max_date() do
+    # See RFC 5280 4.1.2.5.2
+    %DateTime{
+      year: 9999,
+      month: 12,
+      day: 31,
+      hour: 23,
+      minute: 59,
+      second: 59,
+      microsecond: {0, 0},
+      std_offset: 0,
+      utc_offset: 0,
+      zone_abbr: "UTC",
+      time_zone: "Etc/UTC"
+    }
+  end
+
+  defp calc_issue_year(year) when year < 2000, do: 0
+  defp calc_issue_year(year) when year > 2031, do: 31
+  defp calc_issue_year(year), do: year - 2000
+
+  defp calc_expire_years(issue_date, expire_date) do
+    delta_years = expire_date.year - issue_date.year
+    # delta_years has to fit in 5 bytes and 0 = doesn't expire
+    cond do
+      delta_years < 1 -> 1
+      delta_years > 31 -> 0
+      true -> delta_years
+    end
+  end
+end

lib/atecc508a/date.ex

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+defmodule ATECC508A.Date do
+  @moduledoc """
+  Handle the ATECC508's encoded dates
+  """
+
+  @doc """
+  Decode an issue date/expiration bitstring
+  """
+  @spec decode(<<_::24>>) :: {DateTime.t(), DateTime.t()}
+  def decode(<<raw_year::5, month::4, day::5, hour::5, expire_years::5>>) do
+    issue_date = %DateTime{
+      year: raw_year + 2000,
+      month: month,
+      day: day,
+      hour: hour,
+      minute: 0,
+      second: 0,
+      microsecond: {0, 0},
+      std_offset: 0,
+      utc_offset: 0,
+      zone_abbr: "UTC",
+      time_zone: "Etc/UTC"
+    }
+
+    expire_date =
+      if expire_years != 0 do
+        %DateTime{issue_date | year: issue_date.year + expire_years}
+      else
+        # Special "no expiration date"
+        max_date()
+      end
+
+    {issue_date, expire_date}
+  end
+
+  @doc """
+  Encode an issue date/expiration bitstring
+
+  This function can easily lose precision on the dates and times since
+  so little is encoded. If accepting arbitrary datetimes, you'll want
+  to check that the conversion didn't truncate in strange ways.
+
+  Important: the max issue year is 2031!!
+  """
+  @spec encode(DateTime.t(), DateTime.t()) :: <<_::24>>
+  def encode(issue_date, expire_date) do
+    expire_years = calc_expire_years(issue_date, expire_date)
+    issue_year = calc_issue_year(issue_date.year)
+
+    <<issue_year::5, issue_date.month::4, issue_date.day::5, issue_date.hour::5, expire_years::5>>
+  end
+
+  defp max_date() do
+    # See RFC 5280 4.1.2.5.2
+    %DateTime{
+      year: 9999,
+      month: 12,
+      day: 31,
+      hour: 23,
+      minute: 59,
+      second: 59,
+      microsecond: {0, 0},
+      std_offset: 0,
+      utc_offset: 0,
+      zone_abbr: "UTC",
+      time_zone: "Etc/UTC"
+    }
+  end
+
+  defp calc_issue_year(year) when year < 2000, do: 0
+  defp calc_issue_year(year) when year > 2031, do: 31
+  defp calc_issue_year(year), do: year - 2000
+
+  defp calc_expire_years(issue_date, expire_date) do
+    delta_years = expire_date.year - issue_date.year
+    # delta_years has to fit in 5 bytes and 0 = doesn't expire
+    cond do
+      delta_years < 1 -> 1
+      delta_years > 31 -> 0
+      true -> delta_years
+    end
+  end
+end

mix.exs

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+defmodule Atecc508a.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :atecc508a,
+      version: "0.1.0",
+      elixir: "~> 1.7",
+      start_permanent: Mix.env() == :prod,
+      deps: deps()
+    ]
+  end
+
+  # Run "mix help compile.app" to learn about applications.
+  def application do
+    [
+      extra_applications: [:logger]
+    ]
+  end
+
+  # Run "mix help deps" to learn about dependencies.
+  defp deps do
+    [
+      {:x509, "~> 0.3"}
+    ]
+  end
+end

mix.lock

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+%{
+  "x509": {:hex, :x509, "0.3.0", "c6f3db66960c6e4f424d1e6cca5c7d730e0a577af8dc115a613f4560ce1df6d3", [:mix], [], "hexpm"},
+}

test/atecc508a_test.exs

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+defmodule ATECC508ATest do
+  use ExUnit.Case
+  doctest ATECC508A
+
+  test "decodes the date in the spec" do
+    {issue_date, expire_date} = ATECC508A.Date.decode(<<0x75, 0x3E, 0x0E>>)
+
+    assert DateTime.compare(issue_date, %DateTime{
+             year: 2014,
+             month: 10,
+             day: 15,
+             hour: 16,
+             minute: 0,
+             second: 0,
+             microsecond: {0, 0},
+             std_offset: 0,
+             utc_offset: 0,
+             zone_abbr: "UTC",
+             time_zone: "Etc/UTC"
+           })
+
+    assert DateTime.compare(expire_date, %DateTime{
+             year: 2028,
+             month: 10,
+             day: 15,
+             hour: 16,
+             minute: 0,
+             second: 0,
+             microsecond: {0, 0},
+             std_offset: 0,
+             utc_offset: 0,
+             zone_abbr: "UTC",
+             time_zone: "Etc/UTC"
+           })
+  end
+
+  test "encodes the date in the spec" do
+    issue_date = %DateTime{
+      year: 2014,
+      month: 10,
+      day: 15,
+      hour: 16,
+      minute: 0,
+      second: 0,
+      microsecond: {0, 0},
+      std_offset: 0,
+      utc_offset: 0,
+      zone_abbr: "UTC",
+      time_zone: "Etc/UTC"
+    }
+
+    expire_date = %DateTime{
+      year: 2028,
+      month: 10,
+      day: 15,
+      hour: 16,
+      minute: 0,
+      second: 0,
+      microsecond: {0, 0},
+      std_offset: 0,
+      utc_offset: 0,
+      zone_abbr: "UTC",
+      time_zone: "Etc/UTC"
+    }
+
+    assert ATECC508A.Date.encode(issue_date, expire_date) == <<0x75, 0x3E, 0xE>>
+  end
+end

test/test_helper.exs

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+ExUnit.start()