allow pre generation of srpA

Author: hbmartin

amplifyframework/src/commonMain/kotlin/com/jump/sdk/amplifyframework/SRPHelper.kt

@@ -27,6 +27,7 @@ import org.kotlincrypto.macs.hmac.sha2.HmacSHA256
 import kotlin.coroutines.cancellation.CancellationException
 import kotlin.io.encoding.Base64
 import kotlin.io.encoding.ExperimentalEncodingApi
+import kotlinx.coroutines.delay
 
 private const val EPHEMERAL_KEY_LENGTH = 1024
 private const val HEX = 16
@@ -47,9 +48,12 @@ private const val HEX_N =
 
 // precomputed: k = H(g|N)
 private val kByteArray = byteArrayOf(83, -126, -126, -60, 53, 71, 66, -41, -53, -67, -30, 53, -97, -49, 103, -7, -11, -77, -90, -80, -121, -111, -27, 1, 27, 67, -72, -91, -74, 109, -98, -26)
+
 // precomputed: N = BigInteger.parseString(HEX_N, 16)
 private val nByteArray = byteArrayOf(0, -1, -1, -1, -1, -1, -1, -1, -1, -55, 15, -38, -94, 33, 104, -62, 52, -60, -58, 98, -117, -128, -36, 28, -47, 41, 2, 78, 8, -118, 103, -52, 116, 2, 11, -66, -90, 59, 19, -101, 34, 81, 74, 8, 121, -114, 52, 4, -35, -17, -107, 25, -77, -51, 58, 67, 27, 48, 43, 10, 109, -14, 95, 20, 55, 79, -31, 53, 109, 109, 81, -62, 69, -28, -123, -75, 118, 98, 94, 126, -58, -12, 76, 66, -23, -90, 55, -19, 107, 11, -1, 92, -74, -12, 6, -73, -19, -18, 56, 107, -5, 90, -119, -97, -91, -82, -97, 36, 17, 124, 75, 31, -26, 73, 40, 102, 81, -20, -28, 91, 61, -62, 0, 124, -72, -95, 99, -65, 5, -104, -38, 72, 54, 28, 85, -45, -102, 105, 22, 63, -88, -3, 36, -49, 95, -125, 101, 93, 35, -36, -93, -83, -106, 28, 98, -13, 86, 32, -123, 82, -69, -98, -43, 41, 7, 112, -106, -106, 109, 103, 12, 53, 78, 74, -68, -104, 4, -15, 116, 108, 8, -54, 24, 33, 124, 50, -112, 94, 70, 46, 54, -50, 59, -29, -98, 119, 44, 24, 14, -122, 3, -101, 39, -125, -94, -20, 7, -94, -113, -75, -59, 93, -16, 111, 76, 82, -55, -34, 43, -53, -10, -107, 88, 23, 24, 57, -107, 73, 124, -22, -107, 106, -27, 21, -46, 38, 24, -104, -6, 5, 16, 21, 114, -114, 90, -118, -86, -60, 45, -83, 51, 23, 13, 4, 80, 122, 51, -88, 85, 33, -85, -33, 28, -70, 100, -20, -5, -123, 4, 88, -37, -17, 10, -118, -22, 113, 87, 93, 6, 12, 125, -77, -105, 15, -123, -90, -31, -28, -57, -85, -11, -82, -116, -37, 9, 51, -41, 30, -116, -108, -32, 74, 37, 97, -99, -50, -29, -46, 38, 26, -46, -18, 107, -15, 47, -6, 6, -39, -118, 8, 100, -40, 118, 2, 115, 62, -56, 106, 100, 82, 31, 43, 24, 23, 123, 32, 12, -69, -31, 23, 87, 122, 97, 93, 108, 119, 9, -120, -64, -70, -39, 70, -30, 8, -30, 79, -96, 116, -27, -85, 49, 67, -37, 91, -4, -32, -3, 16, -114, 75, -126, -47, 32, -87, 58, -46, -54, -1, -1, -1, -1, -1, -1, -1, -1)
 
+private enum class SrpGenerationState { NOT_STARTED, STARTED, COMPLETED }
+
 @OptIn(ExperimentalEncodingApi::class)
 @Suppress("TooManyFunctions")
 class SRPHelper(userPool: String) {
@@ -62,8 +66,9 @@ class SRPHelper(userPool: String) {
     private val random = SecureRandom()
 
     private val k: BigInteger = BigInteger.fromTwosComplementByteArray(kByteArray)
-    lateinit var privateA: BigInteger
-    lateinit var publicA: ModularBigInteger
+    private var srpState: SrpGenerationState = SrpGenerationState.NOT_STARTED
+    private lateinit var privateA: BigInteger
+    private lateinit var publicA: ModularBigInteger
     var timestamp: String = nowAsFormattedString()
         internal set
 
@@ -79,14 +84,28 @@ class SRPHelper(userPool: String) {
     }
 
     // Generate client private 'a' and public 'A' values
-    suspend fun getPublicA(): String {
-        do {
-            privateA = BigInteger.fromByteArray(random.nextBytesOf(EPHEMERAL_KEY_LENGTH), Sign.POSITIVE).mod(N)
-            // A = (g ^ a) % N
-            publicA = g.pow(privateA)
-        } while (publicA.residue == BigInteger.ZERO)
-        return publicA.toString(HEX)
-    }
+    suspend fun getPublicA(): String =
+        when (srpState) {
+            SrpGenerationState.NOT_STARTED -> {
+                do {
+                    privateA = BigInteger
+                        .fromByteArray(
+                            source = random.nextBytesOf(EPHEMERAL_KEY_LENGTH),
+                            sign = Sign.POSITIVE,
+                        )
+                        .mod(N)
+                    // A = (g ^ a) % N
+                    publicA = g.pow(privateA)
+                } while (publicA.residue == BigInteger.ZERO)
+                publicA.toString(HEX)
+            }
+
+            SrpGenerationState.STARTED -> {
+                do { delay(10) } while (srpState != SrpGenerationState.COMPLETED)
+                publicA.toString(HEX)
+            }
+            SrpGenerationState.COMPLETED -> publicA.toString(HEX)
+        }
 
     // @TestOnly
     internal fun modN(value: BigInteger): BigInteger = value.mod(N)
@@ -219,4 +238,3 @@ class SRPHelper(userPool: String) {
         return Base64.encode(m1Signature)
     }
 }
-