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唐小鸭
9118a6e344
Single-part encrypted objects in the legacy format could not serve range reads without decrypting from byte 0: v1 frames are emitted per upstream read, so no closed-form plaintext-to-ciphertext mapping exists. The v2 layout fixed the frame length (8218 ciphertext bytes per 8 KiB plaintext frame), making the mapping closed-form. Consume it: - Single-part PUTs that encrypt locally under the v2 write switch stamp the frame-layout marker, valued with the object's data_dir token - ciphertext passthrough, data movement and copies mint a new data_dir or strip the marker, so a re-homed marker disqualifies itself. - The encrypted read plan seeks marked, uncompressed single-part objects to frame_index * 8218 and decrypts from that frame: the frame index rides the plan's sequence-number slot into DecryptReader::new_at_block, whose nonce and AAD bind absolute indices. New metric path label frame_seek. - A lying marker fails closed: v2 authentication rejects bytes at a fake frame boundary; plaintext is never served from the wrong offset. Compressed objects and multipart sub-part seeks keep the conservative paths (follow-up work); reading needs no switch - seekability follows the marker.