Encrypted Office package with non-block-aligned cipher

The AES-CBC/ECB cipher used by Office Standard Encryption requires the cipher body (after the 8-byte declared-size header) to be a multiple of 16 bytes. Excel itself tolerates the misalignment by truncating to the last full block; most strict decryption tools (including antivirus/EDR scanners that introspect inner content) reject the file outright. This asymmetric tolerance is a deliberate evasion shape: the document opens normally in Office but defeats static inspection that depends on a successful decrypt-and-rescan.