Verify Ethereum message signature

Author: Yao Hsu

app/build.gradle

@@ -58,4 +58,7 @@ dependencies {
 
     implementation 'com.google.code.gson:gson:2.8.6'
     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_impl_spongycastle:0.82.4'
 }

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

@@ -104,8 +104,9 @@ class FirstFragment : Fragment() {
                         val photoData = EthereumJsonTemplate(Message(bitmapHash))
                         Log.i(LOG_TAG, "EthereumJson=$photoData")
                         val sig = ByteArrayHolder()
+                        val uniqueId = Utils.getZkmaSdkUniqueId(this.requireContext())
                         val result = ZkmaSdkHelper.signMessage(
-                            Utils.getZkmaSdkUniqueId(this.requireContext()),
+                            uniqueId,
                             COIN_TYPE_ETHEREUM,
                             Gson().toJson(photoData),
                             sig
@@ -114,6 +115,15 @@ class FirstFragment : Fragment() {
                             LOG_TAG,
                             "signMessage(), result=$result, sig=${sig.byteArray.toString()}"
                         )
+                        val verified = ZkmaSdkHelper.verifyEthMsgSignature(
+                            uniqueId,
+                            bitmapHash,
+                            sig.byteArray
+                        )
+                        Log.i(
+                            LOG_TAG,
+                            "verifyEthMsgSignature(), verified=$verified"
+                        )
                     }
                 }
             }

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

@@ -6,7 +6,12 @@ import androidx.annotation.WorkerThread
 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 java.util.concurrent.atomic.AtomicBoolean
+import org.kethereum.crypto.signedMessageToKey
+import org.kethereum.model.SignatureData
+import java.lang.NumberFormatException
+import java.security.SignatureException
 
 class ZkmaSdkHelper {
 
@@ -79,5 +84,30 @@ class ZkmaSdkHelper {
             if (!zkmaSdkInited.get()) throw RuntimeException("ZKMA not initialized!")
             return zkmaManager.signMessage(uniqueId, coinType, strJson, byteArrayHolder)
         }
+
+        @WorkerThread
+        @Synchronized
+        fun verifyEthMsgSignature(
+            uniqueId: Long,
+            message: String,
+            signatureBytes: ByteArray
+        ): Boolean {
+            if (!zkmaSdkInited.get()) throw RuntimeException("ZKMA not initialized!")
+            var verified = false
+            try {
+                val signature = GenericUtils.byteArrayToHex(signatureBytes)
+                val r = signature.slice(0..63).toBigInteger(16)
+                val s = signature.slice(64..127).toBigInteger(16)
+                val v = signature.slice(128..129).toBigInteger()
+                val signatureData = SignatureData(r, s, v)
+                val msgPubKey = signedMessageToKey(message.toByteArray(), signatureData).key
+                val tzPubKey = zkmaManager.getSendPublicKey(uniqueId, 60).key
+                    .substringAfter("0x").toBigInteger(16)
+                verified = tzPubKey == msgPubKey
+            } catch (e: Exception) {
+                Log.e(Utils.LOG_TAG, e.message, e)
+            }
+            return verified
+        }
     }
 }

build.gradle

@@ -18,6 +18,7 @@ allprojects {
     repositories {
         google()
         jcenter()
+        maven { url 'https://jitpack.io' }
     }
 }