feat(ethereum): ✨ recover address from message and signature

src/lua/crypto_ethereum.lua

@@ -252,8 +252,6 @@ function ETH.verifySignatureTransaction(pk, txSigned)
    return ECDH.verify_hashed(pk, txHash, sig, #txHash)
 end
 
-local encode
-
 -- This function defaults to sign_ecdh_deterministic if no sign_function is passed.
 -- One may use the random ECDSA by specifying the "sign_function" parameter as "sign_ecdh".
 function ETH.encodeSignedData(sk, message, sign_function)
@@ -380,6 +378,24 @@ function ETH.address_from_public_key(pk)
    return H:process(pk:sub(2, #pk)):sub(13, 32)
 end
 
+function ETH.address_from_signature(signature, y_parity, hash)
+   local pk, valid
+
+   local x = INT.new(signature.r)
+   local p = ECDH.prime()
+   local n = ECDH.order()
+   local h = ECDH.cofactor() --h=1
+   repeat
+	   pk, valid = ECDH.recovery(x:octet(), y_parity, hash, signature)
+	   if h > 0 then   -- do not add n last iteration
+		   x = (x + n) % p
+	   end
+	   h = h-1
+   until (valid) or (h < 0)
+
+   return valid and ETH.address_from_public_key(pk)
+end
+
 local function encode_uint(val)
    return BIG.new(val):fixed(32)
 end
@@ -403,7 +419,7 @@ end
 
 local encode_tuple
 
-function encode(t, arg)
+local function encode(t, arg)
    local res
    if type(t) == "string" then
       if string.match(t, 'uint%d+$') or t == 'address' then

src/lua/zencode_ethereum.lua

@@ -437,22 +437,23 @@ When("create the ethereum signature of ''", function(object)
     new_codec('ethereum signature')
 end)
 
-IfWhen("verify the '' has a ethereum signature in '' by ''", function(doc, sig, by)
-    local msg = have(doc)
-    local ethersMessage = O.from_string("\x19Ethereum Signed Message:\n") .. O.new(#msg) .. msg
-    local hmsg = keccak256(ethersMessage)
+local function _prepare_msg_f(src)
+    local msg = have(src)
+    local ethers_message = O.from_string("\x19Ethereum Signed Message:\n") .. O.new(#msg) .. msg
+    local hashed_msg = keccak256(ethers_message)
+    return hashed_msg
+end
 
+IfWhen("verify the '' has a ethereum signature in '' by ''", function(doc, sig, by)
+    local hmsg = _prepare_msg_f(doc)
     local signature = have(sig)
     local address = have(by)
     zencode_assert(ETH.verify_signature_from_address(signature, address, fif(signature.v:parity(), 0, 1), hmsg),
             'The ethereum signature by '..by..' is not authentic')
 end)
 
 local function _verify_address_signature_array(add_sig, doc, fun)
-    local msg = have(doc)
-    local ethersMessage = O.from_string("\x19Ethereum Signed Message:\n") .. O.new(#msg) .. msg
-    local hmsg = keccak256(ethersMessage)
-
+    local hmsg = _prepare_msg_f(doc)
     local address_signature, address_signature_codec = have(add_sig)
     zencode_assert(address_signature_codec.schema, "The ethereum address signature pair array is not a schema")
     zencode_assert(address_signature_codec.zentype == "a", "The ethereum address signature pair array is not an array")
@@ -504,3 +505,15 @@ When("use the ethereum transaction to run '' using ''", function(m, p)
     zencode_assert(not tx.data or #tx.data == 0, "Cannot overwrite transaction data")
     tx.data = transaction_data
 end)
+
+When("create the ethereum address from the ethereum signature '' of ''", function(sign, doc)
+    empty'ethereum address'
+    local hashed_msg = _prepare_msg_f(doc)
+    local signature = have(sign)
+    local res = ETH.address_from_signature(signature, fif(signature.v:parity(), 0, 1), hashed_msg)
+    if not res then
+        error("No valid address found related to signature :"..sign)
+    end
+    ACK.ethereum_address = res
+    new_codec('ethereum address', { zentype = 'e' , encoding = 'complex'})
+end)

test/zencode/ethereum.bats

@@ -1031,3 +1031,21 @@ EOF
     save_output verification_result.out
     assert_output '{"result_array":[{"address":"0x2B8070975AF995Ef7eb949AE28ee7706B9039504","status":"verified"},{"address":"0x3028806AC293B5aC9b863B685c73813626311DaD","status":"verified"},{"address":"0xe1C2F1ACb2758c4D88EDb84e0306A0a96682E62a","status":"verified"},{"address":"0xe1C2F1ACb2758c4D88EDb84e0306A0a96682E62a","status":"not verified"}]}'
 }
+
+@test "create the ethereum address from the ethereum signature '' of ''" {
+    cat <<EOF | save_asset add_from_sig.data
+{
+    "ethereum_signature": "0xed8f36c71989f8660e8f5d4adbfd8f1c0288cca90d3a5330b7bf735d71ab52fe7ba0a7827dc4ba707431f1c10babd389f658f8e208b89390a9be3c097579a2ff1b",
+    "message": "I love the Beatles, all but 3"
+}
+EOF
+    cat <<EOF | zexe add_from_sig.zen add_from_sig.data
+Scenario ethereum
+Given I have a 'ethereum_signature'
+Given I have a 'string' named 'message'
+When I create the ethereum address from the ethereum signature 'ethereum_signature' of 'message'
+Then print the 'ethereum address'
+EOF
+    save_output 'add_from_sig.json'
+    assert_output '{"ethereum_address":"0x2B8070975AF995Ef7eb949AE28ee7706B9039504"}'
+}