Primer paso de la investigacion. Se aportan el .apk, las carpetas con el apk extraido y el apk descompilado. El archivo API_DOCUMENTATION.md es un archivo donde se anotaran los descubrimientos del funcionamiento de la API, y los .py son scripts para probar la funcionalidad de la API con los métodos que vayamos encontrando. Finalmente, los archivos .js son scripts de Frida para extraer informacion de la APP durante la ejecucion.

apk_decompiled/sources/kotlin/io/encoding/Base64JVMKt.java

@@ -0,0 +1,60 @@
+package kotlin.io.encoding;
+
+import com.google.firebase.analytics.FirebaseAnalytics;
+import java.nio.charset.Charset;
+import kotlin.Metadata;
+import kotlin.SinceKotlin;
+import kotlin.internal.InlineOnly;
+import kotlin.jvm.internal.Intrinsics;
+import kotlin.text.Charsets;
+
+@Metadata(d1 = {"\u0000 \n\u0000\n\u0002\u0010\u0012\n\u0002\u0018\u0002\n\u0000\n\u0002\u0010\r\n\u0000\n\u0002\u0010\b\n\u0002\b\u0006\n\u0002\u0010\u000e\n\u0000\u001a%\u0010\u0000\u001a\u00020\u0001*\u00020\u00022\u0006\u0010\u0003\u001a\u00020\u00042\u0006\u0010\u0005\u001a\u00020\u00062\u0006\u0010\u0007\u001a\u00020\u0006H\u0081\b\u001a5\u0010\b\u001a\u00020\u0006*\u00020\u00022\u0006\u0010\u0003\u001a\u00020\u00012\u0006\u0010\t\u001a\u00020\u00012\u0006\u0010\n\u001a\u00020\u00062\u0006\u0010\u0005\u001a\u00020\u00062\u0006\u0010\u0007\u001a\u00020\u0006H\u0081\b\u001a%\u0010\u000b\u001a\u00020\u0001*\u00020\u00022\u0006\u0010\u0003\u001a\u00020\u00012\u0006\u0010\u0005\u001a\u00020\u00062\u0006\u0010\u0007\u001a\u00020\u0006H\u0081\b\u001a%\u0010\f\u001a\u00020\r*\u00020\u00022\u0006\u0010\u0003\u001a\u00020\u00012\u0006\u0010\u0005\u001a\u00020\u00062\u0006\u0010\u0007\u001a\u00020\u0006H\u0081\b¨\u0006\u000e"}, d2 = {"platformCharsToBytes", "", "Lkotlin/io/encoding/Base64;", "source", "", "startIndex", "", "endIndex", "platformEncodeIntoByteArray", FirebaseAnalytics.Param.DESTINATION, "destinationOffset", "platformEncodeToByteArray", "platformEncodeToString", "", "kotlin-stdlib"}, k = 2, mv = {1, 9, 0}, xi = 48)
+/* loaded from: classes3.dex */
+public final class Base64JVMKt {
+    @ExperimentalEncodingApi
+    @SinceKotlin(version = "1.8")
+    @InlineOnly
+    private static final byte[] platformCharsToBytes(Base64 base64, CharSequence source, int i, int i4) {
+        Intrinsics.checkNotNullParameter(base64, "<this>");
+        Intrinsics.checkNotNullParameter(source, "source");
+        if (!(source instanceof String)) {
+            return base64.charsToBytesImpl$kotlin_stdlib(source, i, i4);
+        }
+        base64.checkSourceBounds$kotlin_stdlib(((String) source).length(), i, i4);
+        String substring = ((String) source).substring(i, i4);
+        Intrinsics.checkNotNullExpressionValue(substring, "substring(...)");
+        Charset charset = Charsets.ISO_8859_1;
+        Intrinsics.checkNotNull(substring, "null cannot be cast to non-null type java.lang.String");
+        byte[] bytes = substring.getBytes(charset);
+        Intrinsics.checkNotNullExpressionValue(bytes, "getBytes(...)");
+        return bytes;
+    }
+
+    @ExperimentalEncodingApi
+    @SinceKotlin(version = "1.8")
+    @InlineOnly
+    private static final int platformEncodeIntoByteArray(Base64 base64, byte[] source, byte[] destination, int i, int i4, int i5) {
+        Intrinsics.checkNotNullParameter(base64, "<this>");
+        Intrinsics.checkNotNullParameter(source, "source");
+        Intrinsics.checkNotNullParameter(destination, "destination");
+        return base64.encodeIntoByteArrayImpl$kotlin_stdlib(source, destination, i, i4, i5);
+    }
+
+    @ExperimentalEncodingApi
+    @SinceKotlin(version = "1.8")
+    @InlineOnly
+    private static final byte[] platformEncodeToByteArray(Base64 base64, byte[] source, int i, int i4) {
+        Intrinsics.checkNotNullParameter(base64, "<this>");
+        Intrinsics.checkNotNullParameter(source, "source");
+        return base64.encodeToByteArrayImpl$kotlin_stdlib(source, i, i4);
+    }
+
+    @ExperimentalEncodingApi
+    @SinceKotlin(version = "1.8")
+    @InlineOnly
+    private static final String platformEncodeToString(Base64 base64, byte[] source, int i, int i4) {
+        Intrinsics.checkNotNullParameter(base64, "<this>");
+        Intrinsics.checkNotNullParameter(source, "source");
+        return new String(base64.encodeToByteArrayImpl$kotlin_stdlib(source, i, i4), Charsets.ISO_8859_1);
+    }
+}