// based on https://github.com/RazTools/Studio/blob/main/AssetStudio/Crypto/UnityCN.cs #include "ArchiveStorageDecryptor.hpp" #include inline unsigned char decrypt_byte(unsigned char *bytes, uint64_t& offset, uint64_t& index, const unsigned char *index_data, const unsigned char *substitute_data) { unsigned char count_byte = substitute_data[((index >> 2) & 3) + 4] + substitute_data[index & 3] + substitute_data[((index >> 4) & 3) + 8] + substitute_data[((unsigned char)index >> 6) + 12]; bytes[offset] = (unsigned char)((index_data[bytes[offset] & 0xF] - count_byte) & 0xF | 0x10 * (index_data[bytes[offset] >> 4] - count_byte)); count_byte = bytes[offset++]; index++; return count_byte; } inline uint64_t decrypt(unsigned char *bytes, uint64_t index, uint64_t remaining, const unsigned char *index_data, const unsigned char *substitute_data) { uint64_t offset = 0; unsigned char current_byte = decrypt_byte(bytes, offset, index, index_data, substitute_data); uint64_t current_byte_high = current_byte >> 4; uint64_t current_byte_low = current_byte & 0xF; if (current_byte_high == 0xF) { unsigned char count_byte; do { count_byte = decrypt_byte(bytes, offset, index, index_data, substitute_data); current_byte_high += count_byte; } while (count_byte == 0xFF); } offset += current_byte_high; if (offset < remaining) { decrypt_byte(bytes, offset, index, index_data, substitute_data); decrypt_byte(bytes, offset, index, index_data, substitute_data); if (current_byte_low == 0xF) { unsigned char count_byte; do { count_byte = decrypt_byte(bytes, offset, index, index_data, substitute_data); } while (count_byte == 0xFF); } } return offset; } PyObject *decrypt_block(PyObject *self, PyObject *args) { Py_buffer index_data; Py_buffer substitute_data; Py_buffer data; uint64_t index; if (!PyArg_ParseTuple(args, "y*y*y*K", &index_data, &substitute_data, &data, &index)) { if (index_data.buf) PyBuffer_Release(&index_data); if (substitute_data.buf) PyBuffer_Release(&substitute_data); if (data.buf) PyBuffer_Release(&data); return NULL; } PyObject *result = PyBytes_FromStringAndSize(NULL, data.len); if (result == NULL) { PyBuffer_Release(&index_data); PyBuffer_Release(&substitute_data); PyBuffer_Release(&data); return NULL; } unsigned char *result_raw = (unsigned char *)PyBytes_AS_STRING(result); memcpy(result_raw, data.buf, data.len); uint64_t offset = 0; while (offset < data.len) { offset += decrypt(result_raw + offset, index++, data.len - offset, (unsigned char *)index_data.buf, (unsigned char *)substitute_data.buf); } PyBuffer_Release(&index_data); PyBuffer_Release(&substitute_data); PyBuffer_Release(&data); return result; }