block_padding/lib.rs
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411
//! Padding and unpadding of messages divided into blocks.
//!
//! This crate provides `Padding` trait which provides padding and unpadding
//! operations. Additionally several common padding schemes are available out
//! of the box.
#![no_std]
#![doc(
html_logo_url = "https://raw.githubusercontent.com/RustCrypto/media/6ee8e381/logo.svg",
html_favicon_url = "https://raw.githubusercontent.com/RustCrypto/media/6ee8e381/logo.svg"
)]
#![cfg_attr(docsrs, feature(doc_cfg))]
#![warn(missing_docs, rust_2018_idioms)]
#[cfg(feature = "std")]
extern crate std;
use core::fmt;
pub use generic_array;
use generic_array::{ArrayLength, GenericArray};
/// Padding types
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
pub enum PadType {
/// Reversible padding
Reversible,
/// Ambiguous padding
Ambiguous,
/// No padding, message must be multiple of block size
NoPadding,
}
/// Trait for padding messages divided into blocks of arbitrary size
pub trait RawPadding {
/// Padding type
const TYPE: PadType;
/// Pads `block` filled with data up to `pos` (i.e length of a message
/// stored in the block is equal to `pos`).
///
/// # Panics
/// If `pos` is bigger than `block.len()`. Most padding algorithms also
/// panic if they are equal.
fn raw_pad(block: &mut [u8], pos: usize);
/// Unpad data in the `block`.
///
/// Returns `Err(UnpadError)` if the block contains malformed padding.
fn raw_unpad(block: &[u8]) -> Result<&[u8], UnpadError>;
}
/// Block size.
pub type Block<B> = GenericArray<u8, B>;
/// Trait for padding messages divided into blocks
pub trait Padding<BlockSize: ArrayLength<u8>> {
/// Padding type
const TYPE: PadType;
/// Pads `block` filled with data up to `pos` (i.e length of a message
/// stored in the block is equal to `pos`).
///
/// # Panics
/// If `pos` is bigger than `BlockSize`. Most padding algorithms also
/// panic if they are equal.
fn pad(block: &mut Block<BlockSize>, pos: usize);
/// Unpad data in the `block`.
///
/// Returns `Err(UnpadError)` if the block contains malformed padding.
fn unpad(block: &Block<BlockSize>) -> Result<&[u8], UnpadError>;
/// Unpad data in the `blocks`.
///
/// Returns `Err(UnpadError)` if the block contains malformed padding.
fn unpad_blocks(blocks: &[Block<BlockSize>]) -> Result<&[u8], UnpadError> {
let bs = BlockSize::USIZE;
let res_len = match (blocks.last(), Self::TYPE) {
(_, PadType::NoPadding) => bs * blocks.len(),
(Some(last_block), _) => {
let n = Self::unpad(last_block)?.len();
assert!(n <= bs);
n + bs * (blocks.len() - 1)
}
(None, PadType::Ambiguous) => 0,
(None, PadType::Reversible) => return Err(UnpadError),
};
// SAFETY: `res_len` is always smaller or equal to `bs * blocks.len()`
Ok(unsafe {
let p = blocks.as_ptr() as *const u8;
core::slice::from_raw_parts(p, res_len)
})
}
}
impl<T, B: ArrayLength<u8>> Padding<B> for T
where
T: RawPadding,
{
const TYPE: PadType = T::TYPE;
#[inline]
fn pad(block: &mut Block<B>, pos: usize) {
T::raw_pad(block.as_mut_slice(), pos);
}
#[inline]
fn unpad(block: &Block<B>) -> Result<&[u8], UnpadError> {
T::raw_unpad(block.as_slice())
}
}
/// Pad block with zeros.
///
/// ```
/// use block_padding::{ZeroPadding, Padding};
/// use generic_array::{GenericArray, typenum::U8};
///
/// let msg = b"test";
/// let pos = msg.len();
/// let mut block: GenericArray::<u8, U8> = [0xff; 8].into();
/// block[..pos].copy_from_slice(msg);
/// ZeroPadding::pad(&mut block, pos);
/// assert_eq!(&block[..], b"test\x00\x00\x00\x00");
/// let res = ZeroPadding::unpad(&mut block).unwrap();
/// assert_eq!(res, msg);
/// ```
///
/// Note that zero padding is not reversible for messages which end
/// with one or more zero bytes.
#[derive(Clone, Copy, Debug)]
pub struct ZeroPadding;
impl RawPadding for ZeroPadding {
const TYPE: PadType = PadType::Ambiguous;
#[inline]
fn raw_pad(block: &mut [u8], pos: usize) {
if pos > block.len() {
panic!("`pos` is bigger than block size");
}
for b in &mut block[pos..] {
*b = 0;
}
}
#[inline]
fn raw_unpad(block: &[u8]) -> Result<&[u8], UnpadError> {
for i in (0..block.len()).rev() {
if block[i] != 0 {
return Ok(&block[..i + 1]);
}
}
Ok(&block[..0])
}
}
/// Pad block with bytes with value equal to the number of bytes added.
///
/// PKCS#7 described in the [RFC 5652](https://tools.ietf.org/html/rfc5652#section-6.3).
///
/// ```
/// use block_padding::{Pkcs7, Padding};
/// use generic_array::{GenericArray, typenum::U8};
///
/// let msg = b"test";
/// let pos = msg.len();
/// let mut block: GenericArray::<u8, U8> = [0xff; 8].into();
/// block[..pos].copy_from_slice(msg);
/// Pkcs7::pad(&mut block, pos);
/// assert_eq!(&block[..], b"test\x04\x04\x04\x04");
/// let res = Pkcs7::unpad(&block).unwrap();
/// assert_eq!(res, msg);
/// ```
#[derive(Clone, Copy, Debug)]
pub struct Pkcs7;
impl Pkcs7 {
#[inline]
fn unpad(block: &[u8], strict: bool) -> Result<&[u8], UnpadError> {
// TODO: use bounds to check it at compile time
if block.len() > 255 {
panic!("block size is too big for PKCS#7");
}
let bs = block.len();
let n = block[bs - 1];
if n == 0 || n as usize > bs {
return Err(UnpadError);
}
let s = bs - n as usize;
if strict && block[s..bs - 1].iter().any(|&v| v != n) {
return Err(UnpadError);
}
Ok(&block[..s])
}
}
impl RawPadding for Pkcs7 {
const TYPE: PadType = PadType::Reversible;
#[inline]
fn raw_pad(block: &mut [u8], pos: usize) {
// TODO: use bounds to check it at compile time for Padding<B>
if block.len() > 255 {
panic!("block size is too big for PKCS#7");
}
if pos >= block.len() {
panic!("`pos` is bigger or equal to block size");
}
let n = (block.len() - pos) as u8;
for b in &mut block[pos..] {
*b = n;
}
}
#[inline]
fn raw_unpad(block: &[u8]) -> Result<&[u8], UnpadError> {
Pkcs7::unpad(block, true)
}
}
/// Pad block with arbitrary bytes ending with value equal to the number of bytes added.
///
/// A variation of PKCS#7 that is less strict when decoding.
///
/// ```
/// use block_padding::{Iso10126, Padding};
/// use generic_array::{GenericArray, typenum::U8};
///
/// let msg = b"test";
/// let pos = msg.len();
/// let mut block: GenericArray::<u8, U8> = [0xff; 8].into();
/// block[..pos].copy_from_slice(msg);
/// Iso10126::pad(&mut block, pos);
/// assert_eq!(&block[..], b"test\x04\x04\x04\x04");
/// let res = Iso10126::unpad(&block).unwrap();
/// assert_eq!(res, msg);
/// ```
#[derive(Clone, Copy, Debug)]
pub struct Iso10126;
impl RawPadding for Iso10126 {
const TYPE: PadType = PadType::Reversible;
#[inline]
fn raw_pad(block: &mut [u8], pos: usize) {
// Instead of generating random bytes as specified by Iso10126 we
// simply use Pkcs7 padding.
Pkcs7::raw_pad(block, pos)
}
#[inline]
fn raw_unpad(block: &[u8]) -> Result<&[u8], UnpadError> {
Pkcs7::unpad(block, false)
}
}
/// Pad block with zeros except the last byte which will be set to the number
/// bytes.
///
/// ```
/// use block_padding::{AnsiX923, Padding};
/// use generic_array::{GenericArray, typenum::U8};
///
/// let msg = b"test";
/// let pos = msg.len();
/// let mut block: GenericArray::<u8, U8> = [0xff; 8].into();
/// block[..pos].copy_from_slice(msg);
/// AnsiX923::pad(&mut block, pos);
/// assert_eq!(&block[..], b"test\x00\x00\x00\x04");
/// let res = AnsiX923::unpad(&block).unwrap();
/// assert_eq!(res, msg);
/// ```
#[derive(Clone, Copy, Debug)]
pub struct AnsiX923;
impl RawPadding for AnsiX923 {
const TYPE: PadType = PadType::Reversible;
#[inline]
fn raw_pad(block: &mut [u8], pos: usize) {
// TODO: use bounds to check it at compile time
if block.len() > 255 {
panic!("block size is too big for PKCS#7");
}
if pos >= block.len() {
panic!("`pos` is bigger or equal to block size");
}
let bs = block.len();
for b in &mut block[pos..bs - 1] {
*b = 0;
}
block[bs - 1] = (bs - pos) as u8;
}
#[inline]
fn raw_unpad(block: &[u8]) -> Result<&[u8], UnpadError> {
// TODO: use bounds to check it at compile time
if block.len() > 255 {
panic!("block size is too big for PKCS#7");
}
let bs = block.len();
let n = block[bs - 1] as usize;
if n == 0 || n > bs {
return Err(UnpadError);
}
let s = bs - n;
if block[s..bs - 1].iter().any(|&v| v != 0) {
return Err(UnpadError);
}
Ok(&block[..s])
}
}
/// Pad block with byte sequence `\x80 00...00 00`.
///
/// ```
/// use block_padding::{Iso7816, Padding};
/// use generic_array::{GenericArray, typenum::U8};
///
/// let msg = b"test";
/// let pos = msg.len();
/// let mut block: GenericArray::<u8, U8> = [0xff; 8].into();
/// block[..pos].copy_from_slice(msg);
/// Iso7816::pad(&mut block, pos);
/// assert_eq!(&block[..], b"test\x80\x00\x00\x00");
/// let res = Iso7816::unpad(&block).unwrap();
/// assert_eq!(res, msg);
/// ```
#[derive(Clone, Copy, Debug)]
pub struct Iso7816;
impl RawPadding for Iso7816 {
const TYPE: PadType = PadType::Reversible;
#[inline]
fn raw_pad(block: &mut [u8], pos: usize) {
if pos >= block.len() {
panic!("`pos` is bigger or equal to block size");
}
block[pos] = 0x80;
for b in &mut block[pos + 1..] {
*b = 0;
}
}
#[inline]
fn raw_unpad(block: &[u8]) -> Result<&[u8], UnpadError> {
for i in (0..block.len()).rev() {
match block[i] {
0x80 => return Ok(&block[..i]),
0x00 => continue,
_ => return Err(UnpadError),
}
}
Err(UnpadError)
}
}
/// Don't pad the data. Useful for key wrapping.
///
/// ```
/// use block_padding::{NoPadding, Padding};
/// use generic_array::{GenericArray, typenum::U8};
///
/// let msg = b"test";
/// let pos = msg.len();
/// let mut block: GenericArray::<u8, U8> = [0xff; 8].into();
/// block[..pos].copy_from_slice(msg);
/// NoPadding::pad(&mut block, pos);
/// assert_eq!(&block[..], b"test\xff\xff\xff\xff");
/// let res = NoPadding::unpad(&block).unwrap();
/// assert_eq!(res, b"test\xff\xff\xff\xff");
/// ```
///
/// Note that even though the passed length of the message is equal to 4,
/// the size of unpadded message is equal to the block size of 8 bytes.
/// Also padded message contains "garbage" bytes stored in the block buffer.
/// Thus `NoPadding` generally should not be used with data length of which
/// is not multiple of block size.
#[derive(Clone, Copy, Debug)]
pub struct NoPadding;
impl RawPadding for NoPadding {
const TYPE: PadType = PadType::NoPadding;
#[inline]
fn raw_pad(block: &mut [u8], pos: usize) {
if pos > block.len() {
panic!("`pos` is bigger than block size");
}
}
#[inline]
fn raw_unpad(block: &[u8]) -> Result<&[u8], UnpadError> {
Ok(block)
}
}
/// Failed unpadding operation error.
#[derive(Clone, Copy, Debug)]
pub struct UnpadError;
impl fmt::Display for UnpadError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
f.write_str("Unpad Error")
}
}
#[cfg(feature = "std")]
#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
impl std::error::Error for UnpadError {}