initial implementation

.credo.exs

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+%{
+  configs: [
+    %{
+      name: "default",
+      files: %{
+        included: [
+          "lib/",
+          "test/"
+        ],
+        excluded: [~r"/_build/", ~r"/deps/"]
+      },
+      plugins: [],
+      requires: [],
+      strict: true,
+      parse_timeout: 5000,
+      color: true,
+      checks: %{
+        enabled: [
+          #
+          ## Consistency Checks
+          #
+          {Credo.Check.Consistency.ExceptionNames, []},
+          {Credo.Check.Consistency.LineEndings, []},
+          {Credo.Check.Consistency.ParameterPatternMatching, []},
+          {Credo.Check.Consistency.SpaceAroundOperators, []},
+          {Credo.Check.Consistency.SpaceInParentheses, []},
+          {Credo.Check.Consistency.TabsOrSpaces, []},
+
+          #
+          ## Design Checks
+          #
+          # You can customize the priority of any check
+          # Priority values are: `low, normal, high, higher`
+          #
+          {Credo.Check.Design.AliasUsage,
+           [priority: :low, if_nested_deeper_than: 2, if_called_more_often_than: 0]},
+          # You can also customize the exit_status of each check.
+          # If you don't want TODO comments to cause `mix credo` to fail, just
+          # set this value to 0 (zero).
+          #
+          {Credo.Check.Design.TagTODO, [exit_status: 0]},
+          {Credo.Check.Design.TagFIXME, []},
+
+          #
+          ## Readability Checks
+          #
+          {Credo.Check.Readability.AliasOrder, []},
+          {Credo.Check.Readability.FunctionNames, []},
+          {Credo.Check.Readability.LargeNumbers, []},
+          {Credo.Check.Readability.MaxLineLength, [priority: :low, max_length: 120]},
+          {Credo.Check.Readability.ModuleAttributeNames, []},
+          {Credo.Check.Readability.ModuleDoc, []},
+          {Credo.Check.Readability.ModuleNames, []},
+          {Credo.Check.Readability.ParenthesesInCondition, []},
+          {Credo.Check.Readability.ParenthesesOnZeroArityDefs, parens: true},
+          {Credo.Check.Readability.PipeIntoAnonymousFunctions, []},
+          {Credo.Check.Readability.PredicateFunctionNames, []},
+          {Credo.Check.Readability.PreferImplicitTry, []},
+          {Credo.Check.Readability.RedundantBlankLines, []},
+          {Credo.Check.Readability.Semicolons, []},
+          {Credo.Check.Readability.SpaceAfterCommas, []},
+          {Credo.Check.Readability.StringSigils, []},
+          {Credo.Check.Readability.TrailingBlankLine, []},
+          {Credo.Check.Readability.TrailingWhiteSpace, []},
+          {Credo.Check.Readability.UnnecessaryAliasExpansion, []},
+          {Credo.Check.Readability.VariableNames, []},
+          {Credo.Check.Readability.WithSingleClause, []},
+
+          #
+          ## Refactoring Opportunities
+          #
+          {Credo.Check.Refactor.Apply, []},
+          {Credo.Check.Refactor.CondStatements, []},
+          {Credo.Check.Refactor.CyclomaticComplexity, []},
+          {Credo.Check.Refactor.FunctionArity, []},
+          {Credo.Check.Refactor.LongQuoteBlocks, []},
+          {Credo.Check.Refactor.MatchInCondition, []},
+          {Credo.Check.Refactor.MapJoin, []},
+          {Credo.Check.Refactor.NegatedConditionsInUnless, []},
+          {Credo.Check.Refactor.NegatedConditionsWithElse, []},
+          {Credo.Check.Refactor.Nesting, []},
+          {Credo.Check.Refactor.UnlessWithElse, []},
+          {Credo.Check.Refactor.WithClauses, []},
+          {Credo.Check.Refactor.FilterCount, []},
+          {Credo.Check.Refactor.FilterFilter, []},
+          {Credo.Check.Refactor.RejectReject, []},
+          {Credo.Check.Refactor.RedundantWithClauseResult, []},
+
+          #
+          ## Warnings
+          #
+          {Credo.Check.Warning.ApplicationConfigInModuleAttribute, []},
+          {Credo.Check.Warning.BoolOperationOnSameValues, []},
+          {Credo.Check.Warning.Dbg, []},
+          {Credo.Check.Warning.ExpensiveEmptyEnumCheck, []},
+          {Credo.Check.Warning.IExPry, []},
+          {Credo.Check.Warning.IoInspect, []},
+          {Credo.Check.Warning.MissedMetadataKeyInLoggerConfig, []},
+          {Credo.Check.Warning.OperationOnSameValues, []},
+          {Credo.Check.Warning.OperationWithConstantResult, []},
+          {Credo.Check.Warning.RaiseInsideRescue, []},
+          {Credo.Check.Warning.SpecWithStruct, []},
+          {Credo.Check.Warning.WrongTestFileExtension, []},
+          {Credo.Check.Warning.UnusedEnumOperation, []},
+          {Credo.Check.Warning.UnusedFileOperation, []},
+          {Credo.Check.Warning.UnusedKeywordOperation, []},
+          {Credo.Check.Warning.UnusedListOperation, []},
+          {Credo.Check.Warning.UnusedPathOperation, []},
+          {Credo.Check.Warning.UnusedRegexOperation, []},
+          {Credo.Check.Warning.UnusedStringOperation, []},
+          {Credo.Check.Warning.UnusedTupleOperation, []},
+          {Credo.Check.Warning.UnsafeExec, []}
+        ],
+        disabled: [
+          #
+          # Checks scheduled for next check update (opt-in for now, just replace `false` with `[]`)
+
+          #
+          # Controversial and experimental checks (opt-in, just move the check to `:enabled`
+          #   and be sure to use `mix credo --strict` to see low priority checks)
+          #
+          {Credo.Check.Consistency.MultiAliasImportRequireUse, []},
+          {Credo.Check.Consistency.UnusedVariableNames, []},
+          {Credo.Check.Design.DuplicatedCode, []},
+          {Credo.Check.Design.SkipTestWithoutComment, []},
+          {Credo.Check.Readability.AliasAs, []},
+          {Credo.Check.Readability.BlockPipe, []},
+          {Credo.Check.Readability.ImplTrue, []},
+          {Credo.Check.Readability.MultiAlias, []},
+          {Credo.Check.Readability.NestedFunctionCalls, []},
+          {Credo.Check.Readability.OneArityFunctionInPipe, []},
+          {Credo.Check.Readability.SeparateAliasRequire, []},
+          {Credo.Check.Readability.SingleFunctionToBlockPipe, []},
+          {Credo.Check.Readability.SinglePipe, []},
+          {Credo.Check.Readability.Specs, []},
+          {Credo.Check.Readability.StrictModuleLayout, []},
+          {Credo.Check.Readability.WithCustomTaggedTuple, []},
+          {Credo.Check.Readability.OnePipePerLine, []},
+          {Credo.Check.Refactor.ABCSize, []},
+          {Credo.Check.Refactor.AppendSingleItem, []},
+          {Credo.Check.Refactor.DoubleBooleanNegation, []},
+          {Credo.Check.Refactor.FilterReject, []},
+          {Credo.Check.Refactor.IoPuts, []},
+          {Credo.Check.Refactor.MapMap, []},
+          {Credo.Check.Refactor.ModuleDependencies, []},
+          {Credo.Check.Refactor.NegatedIsNil, []},
+          {Credo.Check.Refactor.PassAsyncInTestCases, []},
+          {Credo.Check.Refactor.PipeChainStart, []},
+          {Credo.Check.Refactor.RejectFilter, []},
+          {Credo.Check.Refactor.VariableRebinding, []},
+          {Credo.Check.Warning.LazyLogging, []},
+          {Credo.Check.Warning.LeakyEnvironment, []},
+          {Credo.Check.Warning.MapGetUnsafePass, []},
+          {Credo.Check.Warning.MixEnv, []},
+          {Credo.Check.Warning.UnsafeToAtom, []}
+        ]
+      }
+    }
+  ]
+}

.formatter.exs

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

.github/workflows/test.yml

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+name: Test
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+
+    name: Build and test
+    runs-on: ubuntu-latest
+
+    env:
+      MIX_ENV: test
+
+    steps:
+    - uses: actions/checkout@v3
+
+    - name: Set up Elixir
+      uses: erlef/setup-beam@61e01a43a562a89bfc54c7f9a378ff67b03e4a21 # v1.16.0
+      with:
+        elixir-version: '1.15.5' # [Required] Define the Elixir version
+        otp-version: '26.0'      # [Required] Define the Erlang/OTP version
+
+    - name: Restore dependencies cache
+      uses: actions/cache@v3
+      with:
+        path: deps
+        key: ${{ runner.os }}-mix-deps-${{ hashFiles('**/mix.lock') }}
+        restore-keys: ${{ runner.os }}-mix-deps-
+
+    - name: Restore build cache
+      uses: actions/cache@v3
+      with:
+        path: _build
+        key: ${{ runner.os }}-mix-build-${{ hashFiles('**/mix.lock') }}
+        restore-keys: ${{ runner.os }}-mix-build-
+
+    - name: Install dependencies
+      run: mix do deps.get, deps.compile
+
+    - name: Run Credo
+      run: mix credo
+
+    - name: Run tests
+      run: mix test
+
+    - name: Run Dialyzer
+      run: mix dialyzer

.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 third-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").
+x963kdf-*.tar
+
+# Temporary files, for example, from tests.
+/tmp/

LICENSE

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+MIT License
+
+Copyright (c) 2024 Ben Youngblood
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

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+# X963KDF [![Hex Version](https://img.shields.io/hexpm/v/x963kdf.svg)](https://hex.pm/packages/x963kdf) [![Hex Docs](https://img.shields.io/badge/docs-hexpm-blue.svg)](https://hexdocs.pm/x963kdf/)
+
+A pure Elixir implementation of the ANSI X9.63 Key Derivation Function.
+
+## Installation
+
+If [available in Hex](https://hex.pm/docs/publish), the package can be installed
+by adding `x963kdf` to your list of dependencies in `mix.exs`:
+
+```elixir
+def deps do
+  [
+    {:x963kdf, "~> 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/x963kdf>.
+
+## Tests
+
+The test vectors under `text/fixtures` were retrieved from the NIST's
+[Cryptographic Algorithm Validation Program] on 2024-07-17.
+
+[Cryptographic
+Algorithm Validation Program]: https://csrc.nist.gov/projects/cryptographic-algorithm-validation-program/component-testing

lib/x963kdf.ex

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+defmodule X963KDF do
+  @moduledoc """
+  ANSI X9.63 Key Derivation Function (KDF)
+  """
+
+  @type alg :: :crypto.sha1() | :crypto.sha2()
+
+  @supported_algs [:sha, :sha224, :sha256, :sha384, :sha512]
+
+  @doc """
+  Derive a key from a shared secret using the ANSI X9.63 Key Derivation Function (KDF).
+
+  ## Parameters
+
+  * `alg` - the SHA-1 or SHA-2 hash function to use
+  * `shared_secret` - the shared secret
+  * `key_length` - the length of the derived key in bytes
+  * `opts` - additional options
+    * `:shared_data` - additional shared data to include in the key derivation
+  """
+  def derive(alg, shared_secret, key_length, opts \\ []) when alg in @supported_algs do
+    shared_data = Keyword.get(opts, :shared_data, <<>>)
+
+    hashmaxlen = hashmaxlen(alg)
+    hashlen = hashlen(alg)
+
+    cond do
+      byte_size(shared_secret) + byte_size(shared_data) + 4 >= hashmaxlen ->
+        raise ArgumentError,
+              "shared_secret + shared_data + 4 must be less than #{hashmaxlen} bytes"
+
+      key_length >= hashlen * (2 ** 32 - 1) ->
+        raise ArgumentError, "key_length must be less than #{hashlen * (2 ** 32 - 1)}"
+
+      true ->
+        :ok
+    end
+
+    for counter <- 1..ceil(key_length / hashlen)//1, into: <<>> do
+      :crypto.hash(
+        alg,
+        <<shared_secret::binary, counter::big-32, shared_data::binary>>
+      )
+    end
+    |> binary_slice(0, key_length)
+  end
+
+  defp hashlen(:sha), do: 20
+  defp hashlen(:sha224), do: 28
+  defp hashlen(:sha256), do: 32
+  defp hashlen(:sha384), do: 48
+  defp hashlen(:sha512), do: 64
+
+  defp hashmaxlen(alg) when alg in [:sha, :sha224, :sha256], do: 2 ** 61 - 1
+  defp hashmaxlen(alg) when alg in [:sha384, :sha512], do: 2 ** 125 - 1
+end