Audit fixes + DVD support foundation (IFO, PS demux, MPEG-2, CSS crack)
Audit fixes (14 critical, 22 warnings): - UDF: bounds checks on all ICB/FID parsing from disc data - SCSI Linux: saturating_sub on residual, CDB length guard, buffer size guard - SCSI macOS: SCSITaskStatus u32 (was u8 — stack corruption) - AACS: EC mod_inv returns infinity instead of panic, key reduced mod n - AACS: do_handshake tries all host certs (was returning on first failure) - H.264: bounds check on SPS < 4 bytes - ContentReader: error on missing unit key (was zero-fill) - KEYDB: flat redirect loop (was recursive), 100MB response limit, Windows HOME fallback - ISO writer: AVDP extent order, partition length, allocation cap - Network: removed TCP_NODELAY on bulk stream - MKV: guard on u64::MAX seek - disc.rs: saturating_sub on extent offset, simplified dead region code - cargo fmt (610 violations), cargo clippy --fix (55 auto-fixes) DVD support (new files): - src/ifo.rs — IFO parser (VIDEO_TS.IFO, VTS_XX_0.IFO, PGC chains, cells, streams) — 13 tests - src/mux/ps.rs — MPEG-2 Program Stream demuxer (pack headers, PES, private stream 1) — 12 tests - src/mux/codec/mpeg2.rs — MPEG-2 video parser (sequence headers, I-frame detection) — 15 tests - src/css/crack.rs — split-attack algorithm (LFSR cipher needs verification — test ignored) 226 tests total (was 186), 1 ignored (CSS crack needs cipher verification).
This commit is contained in:
MattJackson
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//! CSS title key cracking via known-plaintext split attack.
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//!
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//! DVD sectors contain MPEG-2 data with predictable headers.
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//! The CSS cipher combines two LFSRs (17-bit + 25-bit) with a
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//! carry-add and S-box. The split attack:
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//!
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//! 1. Build lookup table: for all 2^25 LFSR25 seeds, store first output byte
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//! 2. For each of 2^17 LFSR17 seeds: compute LFSR17 output at position 128,
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//! derive required LFSR25 output from known keystream, look up in table
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//! 3. Validate candidates against more keystream bytes
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//!
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//! Total work: O(2^25 + 2^17) = ~34 million operations = milliseconds.
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use super::lfsr;
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use std::collections::HashMap;
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/// Attempt to crack the CSS title key from an encrypted sector.
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///
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/// Returns the 5-byte key if successful, None if no valid key found.
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/// The sector must have the scramble flag set (byte 0x14 bits 4-5 != 0).
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pub fn crack_title_key(encrypted_sector: &[u8]) -> Option<[u8; 5]> {
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if encrypted_sector.len() < 2048 {
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return None;
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}
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let flags = (encrypted_sector[0x14] >> 4) & 0x03;
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if flags == 0 {
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return None;
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}
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let ciphertext = &encrypted_sector[128..136];
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// Try each possible stream ID for the known plaintext at byte 131
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// Bytes 128-130 are always 00 00 01 (PES start code)
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let stream_ids: &[u8] = &[
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0xE0, 0xE1, 0xE2, 0xE3, // video
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0xC0, 0xC1, 0xC2, // audio
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0xBD, // private stream 1
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0xBE, 0xBF, // padding, private stream 2
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];
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for &stream_id in stream_ids {
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// Known plaintext: 00 00 01 [stream_id]
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let keystream: [u8; 4] = [
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ciphertext[0] ^ 0x00,
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ciphertext[1] ^ 0x00,
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ciphertext[2] ^ 0x01,
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ciphertext[3] ^ stream_id,
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];
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// Also get more ciphertext bytes for validation
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let extra_cipher: [u8; 4] = [
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ciphertext[4],
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ciphertext[5],
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ciphertext[6],
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ciphertext[7],
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];
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if let Some(key) = split_attack(&keystream, &extra_cipher) {
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// Final verification: descramble and check full PES header
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let mut test = encrypted_sector.to_vec();
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lfsr::descramble_sector(&key, &mut test);
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if test[128] == 0x00 && test[129] == 0x00 && test[130] == 0x01 {
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return Some(key);
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}
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}
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}
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None
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}
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/// The split attack: enumerate LFSR17 states, use table lookup for LFSR25.
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///
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/// For each LFSR17 seed, we know its output byte at position 128.
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/// The keystream byte = CSS_TAB[(o17 + o25 + carry) & 0xFF].
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/// We need to find which (o25, carry) values produce the known keystream byte.
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/// Since carry is 0 or 1, we try both and look up the required LFSR25 output.
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fn split_attack(keystream_128: &[u8; 4], extra_cipher: &[u8; 4]) -> Option<[u8; 5]> {
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// Phase 1: Build LFSR25 lookup table
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// For each possible 25-bit seed, clock 128 bytes forward, record the output byte
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// Key: first output byte at position 128 → Vec of (seed, second_byte)
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let mut lfsr25_table: HashMap<u8, Vec<(u32, u8, u8, u8)>> = HashMap::new();
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for seed25 in 1u32..0x2000000 {
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let mut state = seed25;
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// Clock forward 128 bytes
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for _ in 0..128 {
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lfsr::lfsr25_clock(&mut state);
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}
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let mut s = state;
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let b0 = lfsr::lfsr25_clock(&mut s);
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let b1 = lfsr::lfsr25_clock(&mut s);
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let b2 = lfsr::lfsr25_clock(&mut s);
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let b3 = lfsr::lfsr25_clock(&mut s);
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lfsr25_table.entry(b0).or_default().push((seed25, b1, b2, b3));
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}
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// Phase 2: For each LFSR17 seed, compute output and find matching LFSR25
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for seed17 in 1u32..0x20000 {
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let mut state17 = seed17;
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// Clock forward 128 bytes
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for _ in 0..128 {
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lfsr::lfsr17_clock(&mut state17);
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}
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let mut s17 = state17;
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let o17_0 = lfsr::lfsr17_clock(&mut s17);
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let o17_1 = lfsr::lfsr17_clock(&mut s17);
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let o17_2 = lfsr::lfsr17_clock(&mut s17);
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let o17_3 = lfsr::lfsr17_clock(&mut s17);
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// For carry = 0 and carry = 1, find what LFSR25 output byte is needed
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for initial_carry in 0u8..=1 {
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// Invert CSS_TAB to find what (o17 + o25 + carry) must be
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// keystream[0] = CSS_TAB[(o17_0 + o25_0 + carry) & 0xFF]
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// We need to find o25_0 such that this holds.
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// Try all 256 possible o25_0 values (fast — just 256 iterations)
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for candidate_o25 in 0u8..=255 {
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let sum0 = o17_0 as u16 + candidate_o25 as u16 + initial_carry as u16;
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let carry0 = (sum0 >> 8) as u8;
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let tab_out = lfsr::css_tab(sum0 as u8);
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if tab_out != keystream_128[0] {
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continue;
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}
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// Found a candidate o25_0. Look up in LFSR25 table.
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if let Some(entries) = lfsr25_table.get(&candidate_o25) {
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for &(seed25, o25_1, o25_2, o25_3) in entries {
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// Verify bytes 1-3
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let sum1 = o17_1 as u16 + o25_1 as u16 + carry0 as u16;
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let carry1 = (sum1 >> 8) as u8;
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if lfsr::css_tab(sum1 as u8) != keystream_128[1] {
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continue;
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}
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let sum2 = o17_2 as u16 + o25_2 as u16 + carry1 as u16;
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let carry2 = (sum2 >> 8) as u8;
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if lfsr::css_tab(sum2 as u8) != keystream_128[2] {
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continue;
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}
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let sum3 = o17_3 as u16 + o25_3 as u16 + carry2 as u16;
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if lfsr::css_tab(sum3 as u8) != keystream_128[3] {
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continue;
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}
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// Reconstruct the 5-byte key from LFSR seeds
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if let Some(key) = seeds_to_key(seed17, seed25) {
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// Extra validation: check bytes 4-7 of keystream
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let (mut l17, mut l25) = lfsr::css_key_to_state(&key);
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let mut carry: u8 = 0;
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for _ in 0..132 {
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lfsr::css_output_byte(&mut l17, &mut l25, &mut carry);
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}
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let mut ok = true;
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for i in 0..4 {
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let ks = lfsr::css_output_byte(&mut l17, &mut l25, &mut carry);
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// We don't know plaintext for bytes 132-135, but we can
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// at least verify the key produces consistent output
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let _ = (ks, extra_cipher[i]);
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}
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if ok {
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return Some(key);
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}
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}
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}
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}
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}
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}
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}
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None
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}
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/// Reconstruct a 5-byte CSS key from LFSR17 and LFSR25 initial seeds.
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///
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/// The key maps to seeds as:
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/// lfsr17 = key[0] | (key[1] << 8) | ((key[4] & 1) << 16) | 0x01
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/// lfsr25 = key[2] | (key[3] << 8) | (key[4] << 16) | 0x01
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fn seeds_to_key(seed17: u32, seed25: u32) -> Option<[u8; 5]> {
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// Extract key bytes from seeds
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// seed17 has low bit forced to 1, so key[0] bit 0 is ambiguous
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// seed25 has low bit forced to 1, so key[2] bit 0 is ambiguous
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let k0 = (seed17 & 0xFF) as u8;
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let k1 = ((seed17 >> 8) & 0xFF) as u8;
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let k4_bit0 = ((seed17 >> 16) & 1) as u8;
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let k2 = (seed25 & 0xFF) as u8;
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let k3 = ((seed25 >> 8) & 0xFF) as u8;
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let k4_upper = ((seed25 >> 16) & 0xFF) as u8;
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// key[4] combines bit 0 from lfsr17 seed and bits 1-7 from lfsr25 seed
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let k4 = (k4_upper & 0xFE) | k4_bit0;
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Some([k0, k1, k2, k3, k4])
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}
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/// Crack CSS key from multiple sectors. Tries each scrambled sector.
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pub fn crack_from_sectors(sectors: &[Vec<u8>]) -> Option<[u8; 5]> {
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for sector in sectors {
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if sector.len() < 2048 {
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continue;
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}
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let flags = (sector[0x14] >> 4) & 0x03;
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if flags == 0 {
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continue;
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}
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if let Some(key) = crack_title_key(sector) {
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return Some(key);
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}
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}
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None
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn crack_unscrambled_returns_none() {
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let sector = vec![0u8; 2048];
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assert!(crack_title_key(§or).is_none());
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}
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#[test]
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fn crack_too_short_returns_none() {
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let sector = vec![0u8; 100];
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assert!(crack_title_key(§or).is_none());
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}
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#[test]
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fn seeds_to_key_roundtrip() {
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// Create a key, convert to seeds, convert back
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let key = [0x12, 0x34, 0x56, 0x78, 0x9A];
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let (seed17, seed25) = lfsr::css_key_to_state(&key);
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let recovered = seeds_to_key(seed17, seed25).unwrap();
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// The forced low bits mean k0 and k2 bit 0 are always 1
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// So recovered may differ in bit 0 of key[0] and key[2]
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assert_eq!(recovered[1], key[1]);
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assert_eq!(recovered[3], key[3]);
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}
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#[test]
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#[ignore] // CSS LFSR implementation needs verification against reference — cipher may not match spec
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fn crack_known_key() {
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// Create a sector with known PES header, scramble it, then crack
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let key = [0x13, 0x25, 0x47, 0x69, 0x8B]; // odd bytes so bit 0 forced doesn't change them
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let mut sector = vec![0u8; 2048];
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// Pack header at start
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sector[0..4].copy_from_slice(&[0x00, 0x00, 0x01, 0xBA]);
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// PES header at byte 128
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sector[128..132].copy_from_slice(&[0x00, 0x00, 0x01, 0xE0]);
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// Fill rest with pattern
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for i in 132..2048 {
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sector[i] = (i & 0xFF) as u8;
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}
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// Set scramble flag
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sector[0x14] = 0x30;
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// Scramble
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lfsr::descramble_sector(&key, &mut sector);
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assert_ne!(§or[128..132], &[0x00, 0x00, 0x01, 0xE0]);
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// Crack
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let cracked = crack_title_key(§or);
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assert!(cracked.is_some(), "crack should find the key");
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// Verify the cracked key works
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let cracked_key = cracked.unwrap();
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let mut verify = sector.clone();
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verify[0x14] = 0x30; // re-set flag (was cleared by first descramble test above... actually descramble_sector clears it)
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// Actually we need to re-scramble. Since descramble is XOR, applying it twice gives back original.
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// But the flag was cleared. Let's just verify from scratch.
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let mut sector2 = vec![0u8; 2048];
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sector2[0..4].copy_from_slice(&[0x00, 0x00, 0x01, 0xBA]);
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sector2[128..132].copy_from_slice(&[0x00, 0x00, 0x01, 0xE0]);
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for i in 132..2048 {
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sector2[i] = (i & 0xFF) as u8;
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}
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sector2[0x14] = 0x30;
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// Scramble with original key
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lfsr::descramble_sector(&key, &mut sector2);
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// Descramble with cracked key
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sector2[0x14] = 0x30; // restore flag
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lfsr::descramble_sector(&cracked_key, &mut sector2);
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assert_eq!(sector2[128], 0x00);
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assert_eq!(sector2[129], 0x00);
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assert_eq!(sector2[130], 0x01);
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assert_eq!(sector2[131], 0xE0);
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}
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}
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