Bring in checksum eth addresses (#37)

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## v1.0.1
+
+  * Brings in Ethereum EIP-55 checksum addresses, credit goes to @wchenNL
+
 ## v1.0.0
 
   **Breaking Changes** 

README.md

@@ -14,7 +14,7 @@ Add the dependency to your `mix.exs`:
 ```
 def deps do
   [
-    {:block_keys, "~> 1.0.0"}
+    {:block_keys, "~> 1.0.1"}
   ]
 end
 ```

lib/block_keys/ethereum/address.ex

@@ -1,6 +1,7 @@
 defmodule BlockKeys.Ethereum.Address do
   @moduledoc """
   Converts a public extended key into an Ethereum Address
+  Follows EIP-55 checksum address encoding: https://eips.ethereum.org/EIPS/eip-55
   """
 
   alias BlockKeys.{Encoding, Crypto}
@@ -9,10 +10,19 @@ defmodule BlockKeys.Ethereum.Address do
     xpub
     |> maybe_decode()
     |> decompress()
-    |> keccak256()
+    |> ExKeccak.hash_256()
     |> to_address()
   end
 
+  def valid_address?("0x" <> address = full_address) when byte_size(address) == 40 do
+    case to_checksum_address(full_address) do
+      {:ok, checksum} -> checksum == full_address
+      _ -> false
+    end
+  end
+
+  def valid_address?(_address), do: false
+
   defp maybe_decode(<<"xpub", _rest::binary>> = encoded_key) do
     decoded_key =
       encoded_key
@@ -31,9 +41,39 @@ defmodule BlockKeys.Ethereum.Address do
   end
 
   defp to_address(<<_::binary-12, address::binary-20>>) do
-    "0x"
-    |> Kernel.<>(address |> Base.encode16(case: :lower))
+    {:ok, checksum_address} =
+      "0x"
+      |> Kernel.<>(address |> Base.encode16(case: :lower))
+      |> to_checksum_address()
+
+    checksum_address
   end
 
-  defp keccak256(data), do: ExKeccak.hash_256(data)
+  defp to_checksum_address("0x" <> address) when byte_size(address) == 40 do
+    address = String.downcase(address)
+
+    checksum =
+      Enum.zip(
+        String.graphemes(address),
+        String.graphemes(address |> ExKeccak.hash_256() |> Base.encode16(case: :lower))
+      )
+      |> Enum.map_join(fn {each_address, each_hash} ->
+        cond do
+          String.match?(each_address, ~r/[0-9]/) ->
+            each_address
+
+          String.match?(each_address, ~r/[a-f]/) and elem(Integer.parse(each_hash, 16), 0) >= 8 ->
+            String.upcase(each_address)
+
+          String.match?(each_address, ~r/[a-f]/) ->
+            each_address
+        end
+      end)
+
+    {:ok, "0x" <> checksum}
+  end
+
+  defp to_checksum_address(_address) do
+    {:error, "unrecognized address"}
+  end
 end

mix.exs

@@ -4,7 +4,7 @@ defmodule BlockKeys.MixProject do
   def project do
     [
       app: :block_keys,
-      version: "1.0.0",
+      version: "1.0.1",
       elixir: "~> 1.7",
       description: description(),
       start_permanent: Mix.env() == :prod,

test/block_keys/ethereum/address_test.exs

@@ -15,6 +15,6 @@ defmodule EthereumAddressTest do
 
     assert CKD.derive(root_key, "M/44'/60'/0'/0/0")
            |> Address.from_xpub() ==
-             "0x73bb50c828fd325c011d740fde78d02528826156"
+             "0x73Bb50c828fD325c011d740fDe78d02528826156"
   end
 end