Struct ApModel 

pub struct ApModel { /* private fields */ }

AP deobfuscation model for a single SA17 page-store file.

Build one with ApModel::learn, then call ApModel::deobfuscate to recover plaintext for any page.

The model is cheap to clone; it stores at most one u8 per 16-page block.

Implementations

impl ApModel

pub fn learn(store: &PageStore) -> Self

Construct an ApModel by scanning every pure-AP page in store.

Pure-AP page types — '@', 'C', 'H', 'M' — have bodies dominated by the AP fill (sectors 1..6 are almost entirely fill). From those sectors we can back-calculate bv(block) precisely.

Pages of other types, whose plaintext is dense, contribute nothing to the calibration. At least one pure-AP page must exist in the store (SA17 files always have some).

pub fn bv_at(&self, bi: u64) -> u8

Return the bv for block bi, falling back to bv0 for unknown blocks.

For files where every block has at least one pure-AP page, every block will be in bv_map. For the rare blocks that lack one, bv0 is used (an approximation that degrades gracefully).

pub fn deobfuscate(&self, raw: &[u8], pn: u64) -> Vec<u8>

Deobfuscate a full 4 KiB page.

pn is the zero-based page index within the store.

The page trailer (0xFF0..0xFFC) and CRC footer (0xFFC..0x1000) are copied verbatim; they are stored in plaintext and must not be modified.

For blocks whose bv was not learned from a pure-AP page this falls back to bv0. Use ApModel::deobfuscate_with_store to get the correct bv for every block.

pub fn learned_block_count(&self) -> usize

Number of blocks for which bv was directly learned from a pure-AP page.

pub fn recover_bv_for_block(&self, store: &PageStore, bi: u64) -> u8

Brute-force recover bv for a block that has no pure-AP page.

For each candidate bv (0..=255), score it by computing the peak of the histogram of (stored[i] - (pn + si - bias) - i*step) mod 256 for each candidate step, then summing the best-step peak across all sectors of up to 3 sample pages in the block. The candidate with the highest total score is returned.

The algorithm matches APModel._recover_bv_for_block in the Python reference implementation. At ~2.7 M arithmetic ops per block it is fast in release mode (< 2 ms on modern hardware).

pub fn deobfuscate_with_store( &self, raw: &[u8], pn: u64, store: &PageStore, ) -> Vec<u8>

Deobfuscate a full 4 KiB page, recovering the block’s bv from the store on demand if it was not learned from pure-AP pages.

Use this variant when you need accurate deobfuscation for blocks that have no pure-AP pages (which is the common case for dense data blocks that consist entirely of ‘E’-type pages).

pub fn deobfuscate_with_bv(&self, raw: &[u8], pn: u64, bv: u8) -> Vec<u8>

Deobfuscate using an explicitly supplied bv.

The caller is responsible for supplying the correct block bv; the model’s internal bv_map is not consulted.

Trait Implementations

impl Clone for ApModel

fn clone(&self) -> ApModel

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for ApModel

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for ApModel

fn default() -> ApModel

Returns the “default value” for a type.