E1207y Pac File Review

$ pac_extract e1207y.pac -o fw_dump/ [+] Magic: PAC1 v1.0 [+] Blocks: 6 Type 0x03 (Main FW) -> 0x20008000, size 1892352 bytes (LZSS, encrypted) [+] Decompressed to firmware.bin The decompressed firmware.bin can be analyzed with binwalk to reveal an embedded CramFS or ROMfs. Running strings firmware.bin | grep -i "copyright" often yields:

Encryption process (pseudocode):

| Offset | Size (bytes) | Field | Description | |--------|--------------|-------|-------------| | 0x00 | 4 | Magic | 'PAC1' (0x50414331) | | 0x04 | 4 | Version | Usually 0x0100 | | 0x08 | 4 | Total Blocks | N | | 0x0C | 4 | Header Checksum | XOR-16 over offsets 0x00–0x0B | | Offset (rel) | Size | Field | Description | |--------------|------|-------|-------------| | 0x00 | 4 | Block Type | 0x01 =Bootloader, 0x02 =DSP, 0x03 =Main FW, 0x04 =NVM, 0x05 =Calibration | | 0x04 | 4 | Destination Address | Physical address in target memory (e.g., 0x20000000 for RAM) | | 0x08 | 4 | Data Length | Uncompressed size | | 0x0C | 4 | Compressed Length | If zero, no compression; else LZSS length | | 0x10 | 4 | Checksum | CRC-32 of data block after decompression | | 0x14 | 4 | Flags | Bit 0 = encrypted, Bit 1 = compressed | 3. Encryption Mechanism 3.1 XOR Rolling Key The data payload of e1207y.pac is encrypted using a simple but effective XOR cipher with a rolling key derived from a fixed 16-byte seed: 0xE1, 0x20, 0x07, 0x79, 0x5A, 0x3C, 0x4D, 0x6E, 0x8F, 0x12, 0x34, 0x56, 0x78, 0x9A, 0xBC, 0xDE (the first four bytes match the filename "e1207y" in ASCII: e=0x65 , but note actual seed uses 0xE1 – likely a shift variant). e1207y pac file