From 2946ac84f8dd13522b417c41c018a162a9539bf9 Mon Sep 17 00:00:00 2001
From: Sean Hinde <sean.hinde@mac.com>
Date: Thu, 12 Jan 2023 15:12:13 +0100
Subject: [PATCH] Updated README

---
 README.md              | 17 +++--------------
 rebar.lock             | 13 ++++++++++++-
 src/ecrecover_util.erl | 28 ++++++++++++++++++++++++++++
 3 files changed, 43 insertions(+), 15 deletions(-)
 create mode 100644 src/ecrecover_util.erl

diff --git a/README.md b/README.md
index 4a12097..41f247f 100644
--- a/README.md
+++ b/README.md
@@ -1,25 +1,14 @@
 # ecrecover
-FFI (NIF) export of Ethereum's ecrecover for use from Erlang.
+FFI (NIF) export of Ethereum's ecrecover for use from Erlang based on
+https://github.com/bitcoin-core/secp256k1.git
 
-### Prerequisites
-The NIF is written in Rust, therefore the following additional build
-dependencies are needed:
-
-- Rust
-- Cargo
-- Cmake
 
 ### Build
 Execute:
 ```
-make
+./rebar3 compile
 ```
 
-To disable the local build of the NIF library, e.g. to use a prebuilt binary,
-use the following command:
-```
-ECRECOVER_DISABLE_NIF_BUILD=true make
-```
 
 ## Erlang integration
 
diff --git a/rebar.lock b/rebar.lock
index 57afcca..2ca880d 100644
--- a/rebar.lock
+++ b/rebar.lock
@@ -1 +1,12 @@
-[].
+{"1.2.0",
+[{<<"hex2bin">>,{pkg,<<"hex2bin">>,<<"1.0.0">>},1},
+ {<<"sha3">>,
+  {git,"https://github.com/aeternity/erlang-sha3",
+       {ref,"b5f27a29ba1179e5907c50d7ec7aa79b2857e981"}},
+  0}]}.
+[
+{pkg_hash,[
+ {<<"hex2bin">>, <<"AAC26EAB998AE80EACEE1C7607C629AB503EBF77A62B9242BAE2B94D47DCB71E">>}]},
+{pkg_hash_ext,[
+ {<<"hex2bin">>, <<"E7012D1D9AADD26E680F0983D26FB8923707F05FAC9688F19F530FA3795E716F">>}]}
+].
diff --git a/src/ecrecover_util.erl b/src/ecrecover_util.erl
new file mode 100644
index 0000000..6d154b7
--- /dev/null
+++ b/src/ecrecover_util.erl
@@ -0,0 +1,28 @@
+-module(ecrecover_util).
+
+-export([ recover_from_hex/1
+        , bin_to_hex/1
+        , hex_to_bin/1
+        ]).
+
+%%=============================================================================
+%% External API
+
+recover_from_hex(Input) ->
+    <<Hash:32/binary, _:31/binary, Sig:65/binary>> = hex_to_bin(Input),
+    PubKey = ecrecover:recover(Hash, Sig),
+    bin_to_hex(PubKey).
+
+bin_to_hex(Bin) ->
+    lists:flatten([io_lib:format("~2.16.0B", [X]) || X <- binary_to_list(Bin)]).
+
+hex_to_bin(S) ->
+    hex_to_bin(S, []).
+hex_to_bin([], Acc) ->
+    list_to_binary(lists:reverse(Acc));
+hex_to_bin([X,Y|T], Acc) ->
+    {ok, [V], []} = io_lib:fread("~16u", [X,Y]),
+    hex_to_bin(T, [V | Acc]);
+hex_to_bin([X|T], Acc) ->
+    {ok, [V], []} = io_lib:fread("~16u", lists:flatten([X,"0"])),
+    hex_to_bin(T, [V | Acc]).