Add web3/metamask-compatible personal_sign and personal_recover, fixes #18

README.md

@@ -92,6 +92,20 @@ Or add a checksum to an existing address:
 Eth::Utils.format_address "0x4bc787699093f11316e819b5692be04a712c4e69" # => "0x4bc787699093f11316e819B5692be04A712C4E69"
 ```
 
+### Personal Signatures
+
+You can recover public keys and generate web3/metamask-compatible signatures:
+
+```ruby
+# Generate signature
+key.personal_sign('hello world')
+
+# Recover signature
+message = 'test'
+signature = '0x3eb24bd327df8c2b614c3f652ec86efe13aa721daf203820241c44861a26d37f2bffc6e03e68fc4c3d8d967054c9cb230ed34339b12ef89d512b42ae5bf8c2ae1c'
+Eth::Key.personal_recover(message, signature) # => 043e5b33f0080491e21f9f5f7566de59a08faabf53edbc3c32aaacc438552b25fdde531f8d1053ced090e9879cbf2b0d1c054e4b25941dab9254d2070f39418afc
+```
+
 ### Configure
 
 In order to prevent replay attacks, you must specify which Ethereum chain your transactions are created for. See [EIP 155](https://github.com/ethereum/EIPs/issues/155) for more detail.

lib/eth/key.rb

@@ -16,6 +16,10 @@ def self.decrypt(data, password)
       new priv: priv
     end
 
+    def self.personal_recover(message, signature)
+      bin_signature = Utils.hex_to_bin(signature).bytes.rotate(-1).pack('c*')
+      OpenSsl.recover_compact(Utils.keccak256(Utils.prefix_message(message)), bin_signature)
+    end
 
     def initialize(priv: nil)
       @private_key = MoneyTree::PrivateKey.new key: priv
@@ -55,6 +59,10 @@ def verify_signature(message, signature)
       public_hex == OpenSsl.recover_compact(hash, signature)
     end
 
+    def personal_sign(message)
+      Utils.bin_to_hex(sign(Utils.prefix_message(message)).bytes.rotate(1).pack('c*'))
+    end
+
 
     private
 

lib/eth/utils.rb

@@ -51,6 +51,10 @@ def bin_to_prefixed_hex(binary)
       prefix_hex bin_to_hex(binary)
     end
 
+    def prefix_message(message)
+      "\x19Ethereum Signed Message:\n#{message.length}#{message}"
+    end
+
     def public_key_to_address(hex)
       bytes = hex_to_bin(hex)
       address_bytes = Utils.keccak256(bytes[1..-1])[-20..-1]

spec/eth/key_spec.rb

@@ -48,6 +48,29 @@
     end
   end
 
+  describe "#personal_sign" do
+    let(:message) { "Hi Mom!" }
+
+    it "signs a message so that the public key can be recovered with personal_recover" do
+      10.times do
+        signature = key.personal_sign message
+        expect(Eth::Key.personal_recover message, signature).to eq(key.public_hex)
+      end
+    end
+  end
+
+  describe ".personal_recover" do
+    let(:message) { "test" }
+    let(:signature) { "3eb24bd327df8c2b614c3f652ec86efe13aa721daf203820241c44861a26d37f2bffc6e03e68fc4c3d8d967054c9cb230ed34339b12ef89d512b42ae5bf8c2ae1c" }
+    let(:public_hex) { "043e5b33f0080491e21f9f5f7566de59a08faabf53edbc3c32aaacc438552b25fdde531f8d1053ced090e9879cbf2b0d1c054e4b25941dab9254d2070f39418afc" }
+
+    it "it can recover a public key from a signature generated with web3/metamask" do
+      10.times do
+        expect(Eth::Key.personal_recover message, signature).to eq(public_hex)
+      end
+    end
+  end
+
   describe "#verify_signature" do
     let(:priv) { '5a37533acfa3ff9386aed01e16c0e7a79038ce05cc383e290d360b8ce9cd6fdf' }
     let(:signature) { hex_to_bin "1ce2f13b4123a23a4a280ac4adcba1ffa3f3848f494dc1de440af43f677e0e01260fb4667ed117d555659b249702c8215162b3f0ee09628813a4ef83616f99f180" }