Avoid BigInteger(int, byte[], int, int) for Android 12 and older

CHANGELOG.md

@@ -4,6 +4,13 @@
 
 Changes for library users since `0.6.3`.
 
+### Fixed
+
+- ECDSA host keys and NIST ECDH key exchange no longer fail with
+  `NoSuchMethodError` on Android 12 and older: EC points are decoded without
+  `BigInteger(int, byte[], int, int)`, which Android has only since API 33.
+  The failure killed the app when the server sent its host keys after login.
+
 ## [0.6.3][0.6.3]
 
 Changes for library users since `0.6.2`.

sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/EcdhKeyExchange.kt

@@ -154,8 +154,9 @@ internal class EcdhKeyExchange(private val curveName: String) : KexAlgorithm {
         if (encoded.isEmpty() || encoded[0] != 0x04.toByte() || encoded.size != 1 + 2 * fieldSize) {
             throw SshException("Invalid EC point encoding")
         }
-        val x = BigInteger(1, encoded, 1, fieldSize)
-        val y = BigInteger(1, encoded, 1 + fieldSize, fieldSize)
+        // BigInteger(int, byte[], int, int) is missing before Android 13 (API 33).
+        val x = BigInteger(1, encoded.copyOfRange(1, 1 + fieldSize))
+        val y = BigInteger(1, encoded.copyOfRange(1 + fieldSize, encoded.size))
         val p = (ecParameterSpec.curve.field as ECFieldFp).p
         if (x >= p || y >= p ||
             y.multiply(y).mod(p) != x.multiply(x).multiply(x).add(ecParameterSpec.curve.a.multiply(x)).add(ecParameterSpec.curve.b).mod(p)

sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/EcdsaSignatureAlgorithm.kt

@@ -69,8 +69,9 @@ internal object EcdsaSignatureAlgorithm : SshSignatureAlgorithm {
         if (encoded[0] != 0x04.toByte() || encoded.size != 1 + 2 * fieldSize) {
             throw SshException("Invalid EC point encoding")
         }
-        val x = BigInteger(1, encoded, 1, fieldSize)
-        val y = BigInteger(1, encoded, 1 + fieldSize, fieldSize)
+        // BigInteger(int, byte[], int, int) is missing before Android 13 (API 33).
+        val x = BigInteger(1, encoded.copyOfRange(1, 1 + fieldSize))
+        val y = BigInteger(1, encoded.copyOfRange(1 + fieldSize, encoded.size))
         return ECPoint(x, y)
     }