Part 2 - Verify Ethereum message signature

1. Convert message to be signed in HEX format
2. Convert message to be verified in EIP-191 format
3. Compare public keys in compressed format

Author: Yao Hsu

app/build.gradle

@@ -60,5 +60,7 @@ dependencies {
     implementation(name:'HtcWalletSDK-Htc_partner1-release', ext:'aar')
     implementation 'com.github.komputing.kethereum:model:0.82.4'
     implementation 'com.github.komputing.kethereum:crypto:0.82.4'
+    implementation 'com.github.komputing.kethereum:crypto_api:0.82.4'
     implementation 'com.github.komputing.kethereum:crypto_impl_spongycastle:0.82.4'
+    implementation 'com.github.komputing.kethereum:extensions_kotlin:0.82.4'
 }

app/src/main/java/com/htc/zion/demoapp/FirstFragment.kt

@@ -12,6 +12,7 @@ import androidx.fragment.app.Fragment
 import com.google.android.material.snackbar.Snackbar
 import com.google.gson.Gson
 import com.htc.htcwalletsdk.Native.Type.ByteArrayHolder
+import com.htc.htcwalletsdk.Utils.GenericUtils
 import com.htc.zion.demoapp.Utils.Companion.LOG_TAG
 import com.htc.zion.demoapp.Utils.Companion.convertToHex
 import com.htc.zion.demoapp.Utils.Companion.sha256
@@ -100,8 +101,9 @@ class FirstFragment : Fragment() {
                         bitmap.convertToHex()
                     }?.let { bitmapHex ->
                         bitmapHex.sha256()
-                    }?.let { bitmapHash ->
-                        val photoData = EthereumJsonTemplate(Message(bitmapHash))
+                    }?.let { msg ->
+                        val msgHex = GenericUtils.byteArrayToHex(msg.toByteArray())
+                        val photoData = EthereumJsonTemplate(Message(msgHex))
                         Log.i(LOG_TAG, "EthereumJson=$photoData")
                         val sig = ByteArrayHolder()
                         val uniqueId = Utils.getZkmaSdkUniqueId(this.requireContext())
@@ -117,7 +119,7 @@ class FirstFragment : Fragment() {
                         )
                         val verified = ZkmaSdkHelper.verifyEthMsgSignature(
                             uniqueId,
-                            bitmapHash,
+                            msg,
                             sig.byteArray
                         )
                         Log.i(

app/src/main/java/com/htc/zion/demoapp/ZkmaSdkHelper.kt

@@ -7,11 +7,15 @@ import com.htc.htcwalletsdk.Export.HtcWalletSdkManager
 import com.htc.htcwalletsdk.Export.RESULT
 import com.htc.htcwalletsdk.Native.Type.ByteArrayHolder
 import com.htc.htcwalletsdk.Utils.GenericUtils
+import org.kethereum.crypto.CURVE
 import java.util.concurrent.atomic.AtomicBoolean
 import org.kethereum.crypto.signedMessageToKey
+import org.kethereum.extensions.toBigInteger
+import org.kethereum.extensions.toBytesPadded
+import org.kethereum.extensions.toHexStringZeroPadded
+import org.kethereum.model.PUBLIC_KEY_SIZE
 import org.kethereum.model.SignatureData
-import java.lang.NumberFormatException
-import java.security.SignatureException
+import java.math.BigInteger
 
 class ZkmaSdkHelper {
 
@@ -96,18 +100,33 @@ class ZkmaSdkHelper {
             var verified = false
             try {
                 val signature = GenericUtils.byteArrayToHex(signatureBytes)
+                Log.d(Utils.LOG_TAG, "signature: $signature")
                 val r = signature.slice(0..63).toBigInteger(16)
                 val s = signature.slice(64..127).toBigInteger(16)
-                val v = signature.slice(128..129).toBigInteger()
+                val v = signature.slice(128..129).toBigInteger(16)
                 val signatureData = SignatureData(r, s, v)
-                val msgPubKey = signedMessageToKey(message.toByteArray(), signatureData).key
+                val signedMsgBytes = message.toByteArray().let {
+                    "\u0019Ethereum Signed Message:\n${it.size}".toByteArray() + it
+                }
+                val msgPubKey = compressKey(signedMessageToKey(signedMsgBytes, signatureData).key)
+                val msgPubKeyHex = msgPubKey.toHexStringZeroPadded(66, false)
+                Log.d(Utils.LOG_TAG, "msgPubKey: $msgPubKeyHex")
                 val tzPubKey = zkmaManager.getSendPublicKey(uniqueId, 60).key
-                    .substringAfter("0x").toBigInteger(16)
+                    .toBigInteger(16)
+                val tzPubKeyHex = tzPubKey.toHexStringZeroPadded(66, false)
+                Log.d(Utils.LOG_TAG, "tzPubKey: $tzPubKeyHex")
                 verified = tzPubKey == msgPubKey
             } catch (e: Exception) {
                 Log.e(Utils.LOG_TAG, e.message, e)
             }
             return verified
         }
+
+        fun compressKey(publicKey: BigInteger): BigInteger {
+            val ret = publicKey.toBytesPadded(PUBLIC_KEY_SIZE + 1)
+            ret[0] = 4
+            val point = CURVE.decodePoint(ret)
+            return point.encoded(true).toBigInteger()
+        }
     }
 }