What conditions must be met for the known-plaintext attack to work on Zyxel firmware ZIP files?

Three conditions are required: (1) The complete plaintext file and the encrypted ZIP must be known; (2) The plaintext file must be compressed using the same algorithm as the target encrypted file (e.g., for `536ABHL0C0.bin`, the `536ABHL0C0.conf` file matches `system-default.conf` and must be compressed with ‘compress better’ or ‘Maximum Compression’); (3) The encryption algorithm used in the ZIP must be ZipCrypto Store.