Momoko-Ayase/Senbei
1
1
Fork 0
mirror of https://github.com/Momoko-Ayase/Senbei.git synced 2026-09-19 03:57:59 -04:00
Code Issues Activity

refactor: consolidate platform engines into senbei-engine

Browse Source
This commit is contained in:
bfloat16
2026-09-06 19:31:19 +08:00
parent cbfacbc31f
commit d436a200ba
66 changed files with 1148 additions and 1012 deletions
Download Patch File Download Diff File Expand all files Collapse all files
senbei-crypto/src/android/protector.rs
+719
View File
@@ -0,0 +1,719 @@
//! Cryptographic and compression primitives used by the Android protector.
use aes::Aes256;
use aes::cipher::{BlockCipherDecrypt, KeyInit};
const RECORD_SIZE: usize = 0x5c;
/// Errors raised while parsing or decoding protector containers.
#[derive(Debug, thiserror::Error)]
pub enum Error {
#[error("{0}")]
Invalid(String),
}
type Result<T> = std::result::Result<T, Error>;
fn invalid<T>(message: impl Into<String>) -> Result<T> {
Err(Error::Invalid(message.into()))
}
fn range(data: &[u8], offset: usize, size: usize) -> Result<&[u8]> {
let end = offset
.checked_add(size)
.ok_or_else(|| Error::Invalid("byte range overflow".to_owned()))?;
data.get(offset..end).ok_or_else(|| {
Error::Invalid(format!(
"byte range 0x{offset:x}..0x{end:x} is out of bounds"
))
})
}
fn read_u16(data: &[u8], offset: usize) -> Result<u16> {
let bytes: [u8; 2] = range(data, offset, 2)?
.try_into()
.map_err(|_| Error::Invalid("invalid u16 range".to_owned()))?;
Ok(u16::from_le_bytes(bytes))
}
fn read_u32(data: &[u8], offset: usize) -> Result<u32> {
let bytes: [u8; 4] = range(data, offset, 4)?
.try_into()
.map_err(|_| Error::Invalid("invalid u32 range".to_owned()))?;
Ok(u32::from_le_bytes(bytes))
}
fn align_up(value: usize, alignment: usize) -> Result<usize> {
let mask = alignment
.checked_sub(1)
.ok_or_else(|| Error::Invalid("zero alignment".to_owned()))?;
value
.checked_add(mask)
.map(|v| v & !mask)
.ok_or_else(|| Error::Invalid("alignment overflow".to_owned()))
}
/// Multiply by the fixed element used by the native GF(2^32) transform.
#[must_use]
pub fn gf32_mul_fixed(mut value: u32) -> u32 {
let mut multiplier = 0x9451_1dd2_u32;
let mut result = 0_u32;
while multiplier != 0 {
if multiplier & 1 != 0 {
result ^= value;
}
let carry = value >> 31;
value = value.wrapping_shl(1);
if carry != 0 {
value ^= 0x5793_57eb;
}
multiplier >>= 1;
}
result
}
fn mix_columns(block: [u8; 16]) -> [u8; 16] {
const fn xtime(value: u8) -> u8 {
(value << 1) ^ if value & 0x80 != 0 { 0x1b } else { 0 }
}
let mut output = [0_u8; 16];
for offset in (0..16).step_by(4) {
let [a, b, c, d] = block[offset..offset + 4] else {
unreachable!("fixed four-byte AES column")
};
output[offset] = xtime(a) ^ (xtime(b) ^ b) ^ c ^ d;
output[offset + 1] = a ^ xtime(b) ^ (xtime(c) ^ c) ^ d;
output[offset + 2] = a ^ b ^ xtime(c) ^ (xtime(d) ^ d);
output[offset + 3] = (xtime(a) ^ a) ^ b ^ c ^ xtime(d);
}
output
}
/// Static configuration recovered from module `0x9B`.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Module9bConfig {
pub header_seed: u32,
pub container_seed: u32,
pub aes_key: [u8; 32],
pub skip_aes: bool,
pub schedule_offset: usize,
}
impl Module9bConfig {
/// Parse the unique AES-256 decryption schedule and adjacent configuration.
pub fn parse(image: &[u8]) -> Result<Self> {
Self::parse_inner(image, true)
}
/// Parse the decoder configuration embedded in the raw Stage 2 image.
///
/// The embedded decoder ends before the interpreter-only `skip_aes`
/// field, so that flag is definitionally false for this layout.
pub fn parse_embedded(image: &[u8]) -> Result<Self> {
Self::parse_inner(image, false)
}
fn parse_inner(image: &[u8], has_skip_aes: bool) -> Result<Self> {
const MARKER: [u8; 4] = [0x00, 0x01, 0x0e, 0x00];
let mut matches = image
.windows(MARKER.len())
.enumerate()
.filter_map(|(offset, bytes)| (bytes == MARKER).then_some(offset));
let schedule_offset = matches
.next()
.ok_or_else(|| Error::Invalid("cannot locate the 0x9B AES-256 schedule".to_owned()))?;
if schedule_offset < 8 || matches.next().is_some() {
return invalid("cannot uniquely locate the 0x9B AES-256 schedule");
}
let header_seed = read_u32(image, schedule_offset - 8)?;
let schedule_size = read_u32(image, schedule_offset - 4)?;
if !matches!(schedule_size, 0 | 0xf4) {
return invalid(format!(
"unexpected 0x9B AES schedule size 0x{schedule_size:x}"
));
}
let bits = read_u16(image, schedule_offset)?;
let rounds = read_u16(image, schedule_offset + 2)?;
if (bits, rounds) != (0x100, 14) {
return invalid(format!(
"unexpected AES schedule header 0x{bits:x}/{rounds}"
));
}
let schedule = range(image, schedule_offset + 4, 15 * 16)?;
let mut round_keys = [[0_u8; 16]; 15];
for (round, output) in round_keys.iter_mut().enumerate() {
let source = &schedule[round * 16..round * 16 + 16];
for word in 0..4 {
let start = word * 4;
for byte in 0..4 {
output[start + byte] = source[start + 3 - byte];
}
}
}
let mut aes_key = [0_u8; 32];
aes_key[..16].copy_from_slice(&round_keys[14]);
aes_key[16..].copy_from_slice(&mix_columns(round_keys[13]));
let container_seed_offset = schedule_offset
.checked_add(0x100)
.ok_or_else(|| Error::Invalid("container seed offset overflow".to_owned()))?;
let skip_aes = if has_skip_aes {
let skip_aes_offset = schedule_offset
.checked_add(0x240)
.ok_or_else(|| Error::Invalid("skip-AES offset overflow".to_owned()))?;
*image.get(skip_aes_offset).ok_or_else(|| {
Error::Invalid("module static configuration exceeds its image".to_owned())
})? != 0
} else {
false
};
Ok(Self {
header_seed,
container_seed: if has_skip_aes {
read_u32(image, container_seed_offset)?
} else {
header_seed
},
aes_key,
skip_aes,
schedule_offset,
})
}
}
/// Decrypted header at the start of direct-data object `0x9D`.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct ProtectedDescriptor {
pub command_id: u32,
pub flags: u32,
pub outer_offset: u32,
pub outer_expected_size: u32,
pub auxiliary_offset: u32,
pub auxiliary_expected_size: u32,
}
impl ProtectedDescriptor {
/// Decrypt the `0x5c`-byte descriptor with the module header seed.
pub fn decrypt(data: &[u8], seed: u32) -> Result<Self> {
if data.len() < RECORD_SIZE {
return invalid("0x9D descriptor is truncated");
}
let base0 = seed.wrapping_add(0xd3e8_7144).wrapping_mul(seed);
let base1 = base0.wrapping_add(seed.wrapping_mul(0x0bd9_418d));
let mut words = [0_u32; RECORD_SIZE / 4];
for (index, word) in words.iter_mut().enumerate() {
let cipher = read_u32(data, index * 4)?;
let subtractor = base0.wrapping_shl(if index & 1 != 0 { 4 } else { 0 });
*word = cipher.wrapping_sub(subtractor)
^ base1.wrapping_shr((seed.wrapping_add((index as u32).wrapping_mul(4))) & 7);
}
if words[6..].iter().any(|&word| word != 0) {
return invalid("unexpected nonzero reserved words in the 0x9D descriptor");
}
let descriptor = Self {
command_id: words[0],
flags: words[1],
outer_offset: words[2],
outer_expected_size: words[3],
auxiliary_offset: words[4],
auxiliary_expected_size: words[5],
};
if descriptor.command_id != 0x9d || descriptor.outer_offset as usize != RECORD_SIZE {
return invalid("unexpected decrypted 0x9D descriptor");
}
Ok(descriptor)
}
}
/// One encrypted segment in a decoded `0x9D` container header.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct EncodedSegment {
pub offset: u32,
pub size: u32,
}
/// Parsed primary or auxiliary `0x9D` container.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct ContainerHeader {
pub start: usize,
pub output_size: u32,
pub skip_aes: bool,
pub tree: Vec<u8>,
pub segments: Vec<EncodedSegment>,
}
impl ContainerHeader {
/// Parse and decrypt a container header, Huffman tree, and segment table.
pub fn parse(data: &[u8], start: usize, seed: u32) -> Result<Self> {
range(data, start, 12)?;
let seed_square = seed.wrapping_mul(seed);
let state = seed_square.wrapping_shr(17) ^ seed_square.wrapping_shl(11);
let raw0 = read_u32(data, start)?;
let raw1 = read_u32(data, start + 4)?;
let raw2 = read_u32(data, start + 8)?;
let output_size = 0xa21d_fb3a_u32
.wrapping_shl(state & 7)
.wrapping_add(state.wrapping_mul(0xf87b_337c))
.wrapping_add(gf32_mul_fixed(raw0));
let flag_word = gf32_mul_fixed(raw1)
^ state
.wrapping_add(0xbd19_c63c)
.wrapping_add(0x416e_2af2_u32.wrapping_shr(state & 0x0d));
let segment_count = (flag_word & 0xff) as usize;
let skip_aes = (flag_word >> 8) & 0xff == 1;
let tree_size = 0x643a_3a3b_u32
.wrapping_shl(state & 0x0b)
.wrapping_sub(state ^ 0x3b2b_f538)
.wrapping_add(gf32_mul_fixed(raw2)) as usize;
if segment_count == 0 || tree_size > 0x1b00 {
return invalid(format!(
"invalid container fields: segments={segment_count}, tree=0x{tree_size:x}"
));
}
let tree_start = start
.checked_add(12)
.ok_or_else(|| Error::Invalid("tree offset overflow".to_owned()))?;
let mut tree = range(data, tree_start, tree_size)?.to_vec();
for offset in (0..tree_size & !3).step_by(4) {
let value = read_u32(&tree, offset)?;
tree[offset..offset + 4].copy_from_slice(&gf32_mul_fixed(value).to_le_bytes());
}
let tree_state = state.wrapping_add(0xf1cb_5b81).wrapping_mul(state);
let tree_delta = tree_state.wrapping_sub(0x23b3_2203_u32.wrapping_mul(state));
for (index, byte) in tree.iter_mut().enumerate() {
let shift = u32::try_from(index & 0x1b)
.map_err(|_| Error::Invalid("tree shift conversion failed".to_owned()))?;
let left = gf32_mul_fixed(tree_state.wrapping_shl(shift));
let right = tree_delta.wrapping_shr((index & 0x17) as u32);
let adjustment = left.wrapping_sub(right).wrapping_shr((index & 0x1f) as u32);
*byte = byte.wrapping_add(adjustment as u8);
}
let table_start = start
.checked_add(align_up(12 + tree_size, 4)?)
.ok_or_else(|| Error::Invalid("segment table offset overflow".to_owned()))?;
let table_size = segment_count
.checked_mul(8)
.ok_or_else(|| Error::Invalid("segment table size overflow".to_owned()))?;
let mut table = range(data, table_start, table_size)?.to_vec();
let table_state = state.wrapping_add(0xb31f_451c).wrapping_mul(state);
let table_xor = table_state.wrapping_shl(3);
let table_add = table_state.wrapping_sub(0x822f_e82d_u32.wrapping_mul(state));
for offset in (0..table_size).step_by(4) {
let value = read_u32(&table, offset)?;
let decoded = gf32_mul_fixed(value ^ table_xor)
.wrapping_add(table_add.wrapping_shr(((offset & 7) + 5) as u32));
table[offset..offset + 4].copy_from_slice(&decoded.to_le_bytes());
}
let mut segments = Vec::with_capacity(segment_count);
for index in 0..segment_count {
let offset = read_u32(&table, index * 8)?;
let size = read_u32(&table, index * 8 + 4)?;
let absolute = start
.checked_add(offset as usize)
.and_then(|value| value.checked_add(size as usize));
if size == 0 || absolute.is_none_or(|end| end > data.len()) {
return invalid(format!("container segment {index} lies outside 0x9D"));
}
segments.push(EncodedSegment { offset, size });
}
Ok(Self {
start,
output_size,
skip_aes,
tree,
segments,
})
}
/// End offset of the furthest encrypted segment.
pub fn encoded_end(&self) -> Result<usize> {
self.segments
.iter()
.map(|segment| {
self.start
.checked_add(segment.offset as usize)
.and_then(|value| value.checked_add(segment.size as usize))
.ok_or_else(|| Error::Invalid("encoded segment end overflow".to_owned()))
})
.collect::<Result<Vec<_>>>()?
.into_iter()
.max()
.ok_or_else(|| Error::Invalid("container has no encoded segments".to_owned()))
}
}
/// Decoder for the protector's Huffman/LZ writer streams.
#[derive(Debug, Clone)]
pub struct HuffmanLzDecoder {
tree: Vec<u8>,
lookup_symbols: Vec<u16>,
lookup_bits: Vec<u8>,
}
impl HuffmanLzDecoder {
/// Build the full 16-bit prefix lookup used by the static decoder.
pub fn new(tree: &[u8]) -> Result<Self> {
if tree.len() < 256 * 3 || !tree.len().is_multiple_of(3) {
return invalid(format!("invalid Huffman tree size 0x{:x}", tree.len()));
}
let mut result = Self {
tree: tree.to_vec(),
lookup_symbols: vec![0; 0x1_0000],
lookup_bits: vec![0; 0x1_0000],
};
for word in 0..0x1_0000_u32 {
let (symbol, bits) = result.decode_symbol(word)?;
if bits <= 16 {
result.lookup_symbols[word as usize] = symbol;
result.lookup_bits[word as usize] = bits;
}
}
Ok(result)
}
fn entry(&self, index: usize) -> Result<(u16, bool, u8)> {
let offset = index
.checked_mul(3)
.ok_or_else(|| Error::Invalid("Huffman node offset overflow".to_owned()))?;
let bytes = range(&self.tree, offset, 3)?;
let raw = u16::from(bytes[0]) | (u16::from(bytes[1]) << 8);
Ok((raw & 0x7fff, raw & 0x8000 != 0, bytes[2]))
}
fn decode_symbol(&self, word: u32) -> Result<(u16, u8)> {
let (mut value, leaf, extra) = self.entry((word & 0xff) as usize)?;
if leaf {
if extra == 0 {
return invalid("zero-width Huffman leaf");
}
return Ok((value, extra));
}
let mut bits = extra
.checked_add(1)
.ok_or_else(|| Error::Invalid("Huffman bit count overflow".to_owned()))?;
let mut mask = 1_u32.wrapping_shl(u32::from(extra));
loop {
let branch = usize::from(word & mask != 0);
let (next, is_leaf, _) = self.entry(usize::from(value) + branch)?;
value = next;
if is_leaf {
return Ok((value, bits));
}
mask = mask.wrapping_shl(1);
bits = bits
.checked_add(1)
.ok_or_else(|| Error::Invalid("Huffman bit count overflow".to_owned()))?;
if bits > 31 {
return invalid("Huffman code exceeds the native 32-bit window");
}
}
}
/// Decode one compressed writer payload to its exact expected size.
pub fn decode(&self, source: &[u8], output_size: usize) -> Result<Vec<u8>> {
let mut output = vec![0_u8; output_size];
let mut source_pos = 0_usize;
let mut bit_buffer = 0_u64;
let mut available = 0_u8;
let mut consumed_bits = 0_usize;
let mut output_pos = 0_usize;
let mut prefix = 0_usize;
while output_pos < output_size {
while available < 24 && source_pos < source.len() {
bit_buffer |= u64::from(source[source_pos]) << available;
source_pos += 1;
available += 8;
}
let key = (bit_buffer & 0xffff) as usize;
let mut bits = self.lookup_bits[key];
let symbol = if bits != 0 {
self.lookup_symbols[key]
} else {
let mut value_offset = ((bit_buffer & 0xff) as usize) * 3;
let mut node = range(&self.tree, value_offset, 3)?;
let mut raw = u16::from(node[0]) | (u16::from(node[1]) << 8);
if raw & 0x8000 != 0 {
bits = node[2];
raw & 0x7fff
} else {
let extra = node[2];
bits = extra + 1;
let mut mask = 1_u64 << extra;
loop {
let branch = usize::from(bit_buffer & mask != 0);
let index = usize::from(raw & 0x7fff) + branch;
value_offset = index
.checked_mul(3)
.ok_or_else(|| Error::Invalid("Huffman node overflow".to_owned()))?;
node = range(&self.tree, value_offset, 3)?;
raw = u16::from(node[0]) | (u16::from(node[1]) << 8);
if raw & 0x8000 != 0 {
break raw & 0x7fff;
}
mask <<= 1;
bits += 1;
}
}
};
if bits == 0 || bits > available {
return invalid("compressed stream ends inside a Huffman code");
}
bit_buffer >>= bits;
available -= bits;
consumed_bits = consumed_bits
.checked_add(usize::from(bits))
.ok_or_else(|| Error::Invalid("consumed bit count overflow".to_owned()))?;
let kind = symbol & 0x300;
let value = usize::from(symbol & 0xff);
match kind {
0 => {
output[output_pos] = value as u8;
output_pos += 1;
}
0x100 => {
if prefix > 0xff {
return invalid("compressed prefix exceeds 16 bits");
}
prefix = if prefix == 0 {
value
} else {
value | (prefix << 8)
};
}
0x200 => {
if prefix == 0 {
prefix = 1;
}
let count = value
.checked_mul(prefix)
.ok_or_else(|| Error::Invalid("repeat count overflow".to_owned()))?;
if !matches!(value, 1 | 2 | 4)
|| value > output_pos
|| output_pos
.checked_add(count)
.is_none_or(|end| end > output_size)
{
return invalid("invalid compressed repeated-pattern command");
}
let pattern = output[output_pos - value..output_pos].to_vec();
for chunk in output[output_pos..output_pos + count].chunks_exact_mut(value) {
chunk.copy_from_slice(&pattern);
}
output_pos += count;
prefix = 0;
}
0x300 => {
let length = value;
let distance = prefix.checked_add(length).ok_or_else(|| {
Error::Invalid("back-reference distance overflow".to_owned())
})?;
if distance > output_pos
|| output_pos
.checked_add(length)
.is_none_or(|end| end > output_size)
{
return invalid("invalid compressed back-reference");
}
let source_start = output_pos - distance;
output.copy_within(source_start..source_start + length, output_pos);
output_pos += length;
prefix = 0;
}
_ => unreachable!("masked Huffman symbol kind"),
}
}
if consumed_bits.div_ceil(8) != source.len() {
return invalid(format!(
"compressed input consumption mismatch: used=0x{:x}, size=0x{:x}",
consumed_bits.div_ceil(8),
source.len()
));
}
Ok(output)
}
}
/// Apply the native word transform and optional AES-256-CBC decryption.
#[allow(clippy::chunks_exact_to_as_chunks)]
pub fn transform_segment(
data: &[u8],
seed: u32,
aes_key: &[u8; 32],
decrypt_aes: bool,
) -> Result<Vec<u8>> {
let mut transformed = data.to_vec();
let mut state = seed;
let mut left = 0xe34e_ac63_u32;
let mut right = 0x07b4_8238_u32;
for (index, chunk) in transformed.chunks_exact_mut(4).enumerate() {
let index32 = u32::try_from(index)
.map_err(|_| Error::Invalid("segment word index exceeds u32".to_owned()))?;
left = state
.wrapping_add(0x72f6_fcbe)
.wrapping_add(left.wrapping_add(0x4f8b_1bca).wrapping_mul(left))
.wrapping_shr(index32.wrapping_mul(index32) & 0x0f);
right = state
.wrapping_sub(0x71b6_a98d)
.wrapping_add(right.wrapping_sub(0x1605_a81c).wrapping_mul(right))
.wrapping_shl(index32 & 7);
state = left ^ right;
let bytes: [u8; 4] = chunk
.try_into()
.map_err(|_| Error::Invalid("invalid transformed word".to_owned()))?;
let mut value = u32::from_le_bytes(bytes);
value = value.wrapping_add(0xb43b_9baf_u32.wrapping_mul(index32 & 0x0d));
value ^= 0xaf57_f7fb_u32.wrapping_mul(index32 & 3);
value = value.wrapping_sub(state) ^ state;
chunk.copy_from_slice(&value.to_le_bytes());
}
if decrypt_aes {
let cipher = Aes256::new_from_slice(aes_key)
.map_err(|_| Error::Invalid("invalid AES-256 key length".to_owned()))?;
let aligned_size = transformed.len() & !0x0f;
let mut previous = [0_u8; 16];
for chunk in transformed[..aligned_size].chunks_exact_mut(16) {
let mut ciphertext = [0_u8; 16];
ciphertext.copy_from_slice(chunk);
// chunk is exactly one block (chunks_exact_mut(16)).
cipher.decrypt_block(chunk.try_into().expect("chunk is one block"));
for (byte, prior) in chunk.iter_mut().zip(previous) {
*byte ^= prior;
}
previous = ciphertext;
}
}
Ok(transformed)
}
/// Decode one complete protector container into its flat output buffer.
///
/// This is the static equivalent of the decoder entrypoint embedded in Stage
/// 2 and in each nested interpreter module.
pub fn decode_container(
data: &[u8],
config: &Module9bConfig,
expected_size: usize,
) -> Result<Vec<u8>> {
let header = ContainerHeader::parse(data, 0, config.container_seed)?;
let header_size = usize::try_from(header.output_size)
.map_err(|_| Error::Invalid("container output size exceeds usize".to_owned()))?;
if header_size != expected_size {
return invalid(format!(
"container output size 0x{header_size:x} != expected 0x{expected_size:x}"
));
}
let decoder = HuffmanLzDecoder::new(&header.tree)?;
let decrypt_aes = !(config.skip_aes || header.skip_aes);
let mut output = vec![0_u8; expected_size];
for (segment_index, encoded) in header.segments.iter().enumerate() {
let start = header
.start
.checked_add(encoded.offset as usize)
.ok_or_else(|| Error::Invalid("encoded segment start overflow".to_owned()))?;
let encoded_data = range(data, start, encoded.size as usize)?;
let transformed = transform_segment(
encoded_data,
config.container_seed,
&config.aes_key,
decrypt_aes,
)?;
if transformed.len() < 16 {
return invalid(format!(
"decoded segment {segment_index} is shorter than its header"
));
}
let base_offset = read_u32(&transformed, 0)? as usize;
let writer_count = read_u32(&transformed, 4)? as usize;
let table_offset = read_u32(&transformed, 8)? as usize;
let data_offset = read_u32(&transformed, 12)? as usize;
let table_size = writer_count
.checked_mul(16)
.ok_or_else(|| Error::Invalid("writer table size overflow".to_owned()))?;
let table_end = table_offset
.checked_add(table_size)
.ok_or_else(|| Error::Invalid("writer table end overflow".to_owned()))?;
if table_end > transformed.len() || data_offset > transformed.len() {
return invalid(format!(
"decoded segment {segment_index} has invalid writer offsets"
));
}
let mut data_cursor = data_offset;
for writer_index in 0..writer_count {
let record =
table_offset
.checked_add(writer_index.checked_mul(16).ok_or_else(|| {
Error::Invalid("writer record offset overflow".to_owned())
})?)
.ok_or_else(|| Error::Invalid("writer record offset overflow".to_owned()))?;
let output_offset = read_u32(&transformed, record)? as usize;
let output_size = read_u32(&transformed, record + 4)? as usize;
let encoded_size = read_u32(&transformed, record + 8)? as usize;
let reserved = read_u32(&transformed, record + 12)?;
let encoded_end = data_cursor
.checked_add(encoded_size)
.ok_or_else(|| Error::Invalid("writer data end overflow".to_owned()))?;
if reserved != 0 || encoded_end > transformed.len() {
return invalid(format!(
"segment {segment_index} writer {writer_index} has invalid bounds"
));
}
let source = &transformed[data_cursor..encoded_end];
let decoded = if encoded_size == output_size {
None
} else {
Some(decoder.decode(source, output_size)?)
};
let decoded = decoded.as_deref().unwrap_or(source);
let target = base_offset
.checked_add(output_offset)
.ok_or_else(|| Error::Invalid("writer target offset overflow".to_owned()))?;
let target_end = target
.checked_add(decoded.len())
.ok_or_else(|| Error::Invalid("writer target end overflow".to_owned()))?;
let destination = output.get_mut(target..target_end).ok_or_else(|| {
Error::Invalid(format!(
"segment {segment_index} writer {writer_index} target is out of range"
))
})?;
destination.copy_from_slice(decoded);
data_cursor = encoded_end;
}
}
Ok(output)
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn aes_mix_columns_matches_fips_example() {
let input = [
0xdb, 0x13, 0x53, 0x45, 0xf2, 0x0a, 0x22, 0x5c, 0x01, 0x01, 0x01, 0x01, 0xc6, 0xc6,
0xc6, 0xc6,
];
assert_eq!(
mix_columns(input),
[
0x8e, 0x4d, 0xa1, 0xbc, 0x9f, 0xdc, 0x58, 0x9d, 0x01, 0x01, 0x01, 0x01, 0xc6, 0xc6,
0xc6, 0xc6,
]
);
}
#[test]
fn descriptor_rejects_truncated_input() {
assert!(ProtectedDescriptor::decrypt(&[0_u8; 16], 1).is_err());
}
}