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#![no_std]
#![cfg_attr(docsrs, feature(doc_cfg))]
#![doc = include_str!("../README.md")]
#![doc(
html_logo_url = "https://raw.githubusercontent.com/RustCrypto/meta/master/logo.svg",
html_favicon_url = "https://raw.githubusercontent.com/RustCrypto/meta/master/logo.svg"
)]
#![deny(unsafe_code)]
#![warn(missing_docs, rust_2018_idioms)]
#![cfg_attr(all(feature = "getrandom", feature = "std"), doc = "```")]
#![cfg_attr(not(all(feature = "getrandom", feature = "std")), doc = "```ignore")]
#![cfg_attr(
all(feature = "getrandom", feature = "heapless", feature = "std"),
doc = "```"
)]
#![cfg_attr(
not(all(feature = "getrandom", feature = "heapless", feature = "std")),
doc = "```ignore"
)]
pub use aead::{self, AeadCore, AeadInPlace, Error, Key, KeyInit, KeySizeUser};
#[cfg(feature = "aes")]
pub use aes;
use cipher::{
consts::{U0, U16},
generic_array::{ArrayLength, GenericArray},
BlockCipher, BlockEncrypt, BlockSizeUser, InnerIvInit, StreamCipherCore,
};
use core::marker::PhantomData;
use ghash::{universal_hash::UniversalHash, GHash};
#[cfg(feature = "zeroize")]
use zeroize::Zeroize;
#[cfg(feature = "aes")]
use aes::{cipher::consts::U12, Aes128, Aes256};
pub const A_MAX: u64 = 1 << 36;
pub const P_MAX: u64 = 1 << 36;
pub const C_MAX: u64 = (1 << 36) + 16;
pub type Nonce<NonceSize> = GenericArray<u8, NonceSize>;
pub type Tag = GenericArray<u8, U16>;
#[cfg(feature = "aes")]
#[cfg_attr(docsrs, doc(cfg(feature = "aes")))]
pub type Aes128Gcm = AesGcm<Aes128, U12>;
#[cfg(feature = "aes")]
#[cfg_attr(docsrs, doc(cfg(feature = "aes")))]
pub type Aes256Gcm = AesGcm<Aes256, U12>;
type Block = GenericArray<u8, U16>;
type Ctr32BE<Aes> = ctr::CtrCore<Aes, ctr::flavors::Ctr32BE>;
#[derive(Clone)]
pub struct AesGcm<Aes, NonceSize> {
cipher: Aes,
ghash: GHash,
nonce_size: PhantomData<NonceSize>,
}
impl<Aes, NonceSize> KeySizeUser for AesGcm<Aes, NonceSize>
where
Aes: KeySizeUser,
{
type KeySize = Aes::KeySize;
}
impl<Aes, NonceSize> KeyInit for AesGcm<Aes, NonceSize>
where
Aes: BlockSizeUser<BlockSize = U16> + BlockEncrypt + KeyInit,
{
fn new(key: &Key<Self>) -> Self {
Aes::new(key).into()
}
}
impl<Aes, NonceSize> From<Aes> for AesGcm<Aes, NonceSize>
where
Aes: BlockSizeUser<BlockSize = U16> + BlockEncrypt,
{
fn from(cipher: Aes) -> Self {
let mut ghash_key = ghash::Key::default();
cipher.encrypt_block(&mut ghash_key);
let ghash = GHash::new(&ghash_key);
#[cfg(feature = "zeroize")]
ghash_key.zeroize();
Self {
cipher,
ghash,
nonce_size: PhantomData,
}
}
}
impl<Aes, NonceSize> AeadCore for AesGcm<Aes, NonceSize>
where
NonceSize: ArrayLength<u8>,
{
type NonceSize = NonceSize;
type TagSize = U16;
type CiphertextOverhead = U0;
}
impl<Aes, NonceSize> AeadInPlace for AesGcm<Aes, NonceSize>
where
Aes: BlockCipher + BlockSizeUser<BlockSize = U16> + BlockEncrypt,
NonceSize: ArrayLength<u8>,
{
fn encrypt_in_place_detached(
&self,
nonce: &Nonce<NonceSize>,
associated_data: &[u8],
buffer: &mut [u8],
) -> Result<Tag, Error> {
if buffer.len() as u64 > P_MAX || associated_data.len() as u64 > A_MAX {
return Err(Error);
}
let (ctr, mask) = self.init_ctr(nonce);
ctr.apply_keystream_partial(buffer.into());
Ok(self.compute_tag(mask, associated_data, buffer))
}
fn decrypt_in_place_detached(
&self,
nonce: &Nonce<NonceSize>,
associated_data: &[u8],
buffer: &mut [u8],
tag: &Tag,
) -> Result<(), Error> {
if buffer.len() as u64 > C_MAX || associated_data.len() as u64 > A_MAX {
return Err(Error);
}
let (ctr, mask) = self.init_ctr(nonce);
let expected_tag = self.compute_tag(mask, associated_data, buffer);
ctr.apply_keystream_partial(buffer.into());
use subtle::ConstantTimeEq;
if expected_tag.ct_eq(tag).into() {
Ok(())
} else {
Err(Error)
}
}
}
impl<Aes, NonceSize> AesGcm<Aes, NonceSize>
where
Aes: BlockCipher + BlockSizeUser<BlockSize = U16> + BlockEncrypt,
NonceSize: ArrayLength<u8>,
{
fn init_ctr(&self, nonce: &Nonce<NonceSize>) -> (Ctr32BE<&Aes>, Block) {
let j0 = if NonceSize::to_usize() == 12 {
let mut block = ghash::Block::default();
block[..12].copy_from_slice(nonce);
block[15] = 1;
block
} else {
let mut ghash = self.ghash.clone();
ghash.update_padded(nonce);
let mut block = ghash::Block::default();
let nonce_bits = (NonceSize::to_usize() as u64) * 8;
block[8..].copy_from_slice(&nonce_bits.to_be_bytes());
ghash.update(&[block]);
ghash.finalize()
};
let mut ctr = Ctr32BE::inner_iv_init(&self.cipher, &j0);
let mut tag_mask = Block::default();
ctr.write_keystream_block(&mut tag_mask);
(ctr, tag_mask)
}
fn compute_tag(&self, mask: Block, associated_data: &[u8], buffer: &[u8]) -> Tag {
let mut ghash = self.ghash.clone();
ghash.update_padded(associated_data);
ghash.update_padded(buffer);
let associated_data_bits = (associated_data.len() as u64) * 8;
let buffer_bits = (buffer.len() as u64) * 8;
let mut block = ghash::Block::default();
block[..8].copy_from_slice(&associated_data_bits.to_be_bytes());
block[8..].copy_from_slice(&buffer_bits.to_be_bytes());
ghash.update(&[block]);
let mut tag = ghash.finalize();
for (a, b) in tag.as_mut_slice().iter_mut().zip(mask.as_slice()) {
*a ^= *b;
}
tag
}
}