refactor: add base 58 check for gateway identity keys (#2312)

nym-vpn-android/core/src/main/java/net/nymtech/vpn/util/Base58.kt

@@ -0,0 +1,45 @@
+package net.nymtech.vpn.util
+
+import java.math.BigInteger
+
+object Base58 {
+	private const val ALPHABET = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
+	private val INDEXES = IntArray(128) { -1 }.also {
+		for (i in ALPHABET.indices) {
+			it[ALPHABET[i].code] = i
+		}
+	}
+
+	fun isValidBase58(input: String, expectedByteLength: Int = 32): Boolean {
+		try {
+			if (input.isEmpty() || input.any { it.code >= 128 || INDEXES[it.code] == -1 }) {
+				return false
+			}
+
+			val bytes = decode(input)
+
+			return bytes.size == expectedByteLength
+		} catch (e: Exception) {
+			return false
+		}
+	}
+
+	private fun decode(input: String): ByteArray {
+		if (input.isEmpty()) return ByteArray(0)
+
+		val bigInt = input.fold(BigInteger.ZERO) { acc, char ->
+			val index = INDEXES[char.code]
+			if (index == -1) throw IllegalArgumentException("Invalid Base58 character: $char")
+			acc.multiply(BigInteger.valueOf(58)).add(BigInteger.valueOf(index.toLong()))
+		}
+
+		val bytes = bigInt.toByteArray()
+
+		val leadingZeros = input.takeWhile { it == '1' }.length
+		return if (bytes[0].toInt() == 0 && bytes.size > 1) {
+			ByteArray(leadingZeros) + bytes.drop(1).toByteArray()
+		} else {
+			ByteArray(leadingZeros) + bytes
+		}
+	}
+}

nym-vpn-android/core/src/main/java/net/nymtech/vpn/util/NotificationManager.kt

@@ -20,7 +20,7 @@ internal class NotificationManager private constructor(val context: Context) {
 		private const val VPN_CHANNEL_ID = "VpnForegroundChannel"
 	}
 
-	fun createNotificationChannel() {
+	private fun createNotificationChannel() {
 		if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
 			// Create the NotificationChannel.
 			val name = context.getString(R.string.channel_name)

nym-vpn-android/core/src/main/java/net/nymtech/vpn/util/extensions/LibExtensions.kt

@@ -1,6 +1,7 @@
 package net.nymtech.vpn.util.extensions
 
 import net.nymtech.vpn.backend.Tunnel
+import net.nymtech.vpn.util.Base58
 import nym_vpn_lib.EntryPoint
 import nym_vpn_lib.ExitPoint
 import nym_vpn_lib.TunnelEvent
@@ -39,16 +40,16 @@ fun String.asEntryPoint(): EntryPoint {
 		this == "random" -> EntryPoint.Random
 		this == "randomlowlatency" -> EntryPoint.RandomLowLatency
 		length == 2 -> EntryPoint.Location(this.uppercase())
-		length == 44 || length == 43 -> EntryPoint.Gateway(this)
+		Base58.isValidBase58(this, 32) -> EntryPoint.Gateway(this)
 		else -> EntryPoint.Random
 	}
 }
 
 fun String.asExitPoint(): ExitPoint {
-	return when (this.length) {
-		2 -> ExitPoint.Location(this.uppercase())
-		134 -> ExitPoint.Address(this)
-		44, 43 -> ExitPoint.Gateway(this)
+	return when {
+		length == 2 -> ExitPoint.Location(this.uppercase())
+		length == 134 -> ExitPoint.Address(this)
+		Base58.isValidBase58(this, 32) -> ExitPoint.Gateway(this)
 		else -> throw IllegalArgumentException("Invalid exit id")
 	}
 }