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/Base64Kt.java

@@ -0,0 +1,79 @@
+package kotlin.io.encoding;
+
+import kotlin.Metadata;
+import kotlin.SinceKotlin;
+import kotlin.collections.ArraysKt___ArraysJvmKt;
+import kotlin.jvm.internal.SourceDebugExtension;
+
+@Metadata(d1 = {"\u0000\u001e\n\u0000\n\u0002\u0010\u0015\n\u0002\b\u0003\n\u0002\u0010\u0012\n\u0002\b\u0004\n\u0002\u0010\u000b\n\u0000\n\u0002\u0010\b\n\u0000\u001a\u0010\u0010\t\u001a\u00020\n2\u0006\u0010\u000b\u001a\u00020\fH\u0001\"\u0016\u0010\u0000\u001a\u00020\u00018\u0002X\u0083\u0004¢\u0006\b\n\u0000\u0012\u0004\b\u0002\u0010\u0003\"\u000e\u0010\u0004\u001a\u00020\u0005X\u0082\u0004¢\u0006\u0002\n\u0000\"\u0016\u0010\u0006\u001a\u00020\u00018\u0002X\u0083\u0004¢\u0006\b\n\u0000\u0012\u0004\b\u0007\u0010\u0003\"\u000e\u0010\b\u001a\u00020\u0005X\u0082\u0004¢\u0006\u0002\n\u0000¨\u0006\r"}, d2 = {"base64DecodeMap", "", "getBase64DecodeMap$annotations", "()V", "base64EncodeMap", "", "base64UrlDecodeMap", "getBase64UrlDecodeMap$annotations", "base64UrlEncodeMap", "isInMimeAlphabet", "", "symbol", "", "kotlin-stdlib"}, k = 2, mv = {1, 9, 0}, xi = 48)
+@SourceDebugExtension({"SMAP\nBase64.kt\nKotlin\n*S Kotlin\n*F\n+ 1 Base64.kt\nkotlin/io/encoding/Base64Kt\n+ 2 _Arrays.kt\nkotlin/collections/ArraysKt___ArraysKt\n*L\n1#1,643:1\n13384#2,3:644\n13384#2,3:647\n*S KotlinDebug\n*F\n+ 1 Base64.kt\nkotlin/io/encoding/Base64Kt\n*L\n580#1:644,3\n597#1:647,3\n*E\n"})
+/* loaded from: classes3.dex */
+public final class Base64Kt {
+    private static final int[] base64DecodeMap;
+    private static final byte[] base64EncodeMap;
+    private static final int[] base64UrlDecodeMap;
+    private static final byte[] base64UrlEncodeMap;
+
+    static {
+        byte[] bArr = {65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 43, 47};
+        base64EncodeMap = bArr;
+        int[] iArr = new int[256];
+        ArraysKt___ArraysJvmKt.fill$default(iArr, -1, 0, 0, 6, (Object) null);
+        iArr[61] = -2;
+        int i = 0;
+        int i4 = 0;
+        int i5 = 0;
+        while (i4 < 64) {
+            iArr[bArr[i4]] = i5;
+            i4++;
+            i5++;
+        }
+        base64DecodeMap = iArr;
+        byte[] bArr2 = {65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 45, 95};
+        base64UrlEncodeMap = bArr2;
+        int[] iArr2 = new int[256];
+        ArraysKt___ArraysJvmKt.fill$default(iArr2, -1, 0, 0, 6, (Object) null);
+        iArr2[61] = -2;
+        int i6 = 0;
+        while (i < 64) {
+            iArr2[bArr2[i]] = i6;
+            i++;
+            i6++;
+        }
+        base64UrlDecodeMap = iArr2;
+    }
+
+    public static final /* synthetic */ int[] access$getBase64DecodeMap$p() {
+        return base64DecodeMap;
+    }
+
+    public static final /* synthetic */ byte[] access$getBase64EncodeMap$p() {
+        return base64EncodeMap;
+    }
+
+    public static final /* synthetic */ int[] access$getBase64UrlDecodeMap$p() {
+        return base64UrlDecodeMap;
+    }
+
+    public static final /* synthetic */ byte[] access$getBase64UrlEncodeMap$p() {
+        return base64UrlEncodeMap;
+    }
+
+    @ExperimentalEncodingApi
+    private static /* synthetic */ void getBase64DecodeMap$annotations() {
+    }
+
+    @ExperimentalEncodingApi
+    private static /* synthetic */ void getBase64UrlDecodeMap$annotations() {
+    }
+
+    @ExperimentalEncodingApi
+    @SinceKotlin(version = "1.8")
+    public static final boolean isInMimeAlphabet(int i) {
+        if (i < 0) {
+            return false;
+        }
+        int[] iArr = base64DecodeMap;
+        return i < iArr.length && iArr[i] != -1;
+    }
+}