Just my poorly organized thoughts and code snippets on reverse engineering Blue Archive
Any help is appreciated
i.e. com.nexon.bluearchive\files\PUB\Resource\Preload\Android\*.bundle
Use AssetStudio
It looks like no major scripting is used there, unlike with, for example, Azur Lane
All code is actually written in C# in Unity, and then compiled with IL2CPP into libil2cpp.so, so no way to extract IL or C# sources
Use Il2CppDumper to extract C# types and generate script to use with Ghidra SRE
Get list from files/TableBundles/TableCatalog.json
stored file name: xxHash64(zip-original-name), etc: 3622299440866786438 => Excel.zip
password: (Pseudocode)
pass := base64.RawStdEncoding.EncodeToString(
CreateKey(
xxHash32.Checksum([]byte(archive.Name), 0)
, 15)
)
func CreateKey(key uint32, length int) []byte {
mt := newMersenneTwister(key)
buf := make([]byte, length)
mt.Read(buf)
return buf
}See IDA function TableService$$LoadBytes
Ref: FlatBuffers
.fbs from il2cppDumper: here, the generator will provided if needs
unpack steps: (partial code, issue welcome if full-code needed)
loadFlatBuffer(new(flat.ScenarioCharacterNameExcelTable))
func loadFlatBuffer[T flatbuffers.FlatBuffer](table T) (T, []byte) {
name := reflect.TypeOf(table).Elem().Name() // "ScenarioCharacterNameExcelTable"
data, err := os.ReadFile(strings.ToLower(name) + ".bytes")
if err != nil {
panic(err)
}
_key := CreateKey(xxHash32.Checksum([]byte(name), 0), len(data))
arr := bArrAsU64Arr(data)
key := bArrAsU64Arr(_key)
for i := range arr {
arr[i] ^= key[i]
}
for i := len(data) - len(data)%8; i < len(data); i++ {
data[i] ^= _key[i]
}
flatbuffers.GetRootAs(data, 0, table)
return table, CreateKeyByString(strings.ReplaceAll(name, "ExcelTable", ""), 8)
}then decrypt value by those:
func decodeAnyScalar[T any](v T, key []byte) T {
size := unsafe.Sizeof(v)
if size < 4 {
return v
}
switch size {
case 4:
if *(*uint32)(unsafe.Pointer(&v)) != 0{
*(*uint32)(unsafe.Pointer(&v)) ^= bArrAsAnyFirst[uint32](key)
}
case 8:
if *(*uint64)(unsafe.Pointer(&v)) != 0{
*(*uint64)(unsafe.Pointer(&v)) ^= bArrAsAnyFirst[uint64](key)
}
default:
b := asArray(unsafe.Pointer(&v), size)
h := false
for i := range b {
if b[i] != 0 {
h = true
break
}
}
if h {
for i := range b {
b[i] ^= key[i]
}
}
}
return v
}
func decodeStr(data []byte, key []byte) string {
if len(data) == 0 {
return `""`
}
raw, err := base64.StdEncoding.DecodeString(string(data))
if err != nil {
panic(err)
}
Xor(raw, key)
d, _ := json.Marshal(string(utf16.Decode(bArrAsU16Arr(raw))))
return string(d)
}