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ocb3: fix nonce and tag size bounds (#595)
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@newpavlov
newpavlov authored Mar 27, 2024
1 parent d2b664b commit 01fcf4c
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Showing 2 changed files with 68 additions and 11 deletions.
1 change: 0 additions & 1 deletion ocb3/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,6 @@ let plaintext = cipher.decrypt(&nonce, ciphertext.as_ref()).unwrap();
assert_eq!(&plaintext, b"plaintext message");
```


## Security Notes

No security audits of this crate have ever been performed, and it has not been thoroughly assessed to ensure its operation is constant-time on common CPU architectures.
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78 changes: 68 additions & 10 deletions ocb3/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -21,7 +21,7 @@ pub use aead::{

use crate::util::{double, inplace_xor, ntz, Block};
use aead::generic_array::{
typenum::{IsGreater, IsGreaterOrEqual, IsLessOrEqual},
typenum::{GrEq, IsGreaterOrEqual, IsLessOrEqual, LeEq, NonZero},
ArrayLength,
};
use cipher::{
Expand Down Expand Up @@ -63,12 +63,49 @@ pub type Tag<TagSize> = GenericArray<u8, TagSize>;
/// - `NonceSize`: max of 15-bytes, default and recommended size of 12-bytes (96-bits).
/// We further restrict the minimum nonce size to 6-bytes to prevent an attack described in
/// the following paper: <https://eprint.iacr.org/2023/326.pdf>.
/// - `TagSize`: max of 16-bytes, default and recommended size of 16-bytes.
/// - `TagSize`: non-zero, max of 16-bytes, default and recommended size of 16-bytes.
///
/// Compilation will fail if the size conditions are not satisfied:
///
/// ```rust,compile_fail
/// # use aes::Aes128;
/// # use ocb3::{aead::{consts::U5, KeyInit}, Ocb3};
/// # let key = [42; 16].into();
/// // Invalid nonce size equal to 5 bytes
/// let cipher = Ocb3::<Aes128, U5>::new(&key);
/// ```
///
/// ```rust,compile_fail
/// # use aes::Aes128;
/// # use ocb3::{aead::{consts::U16, KeyInit}, Ocb3};
/// # let key = [42; 16].into();
/// // Invalid nonce size equal to 16 bytes
/// let cipher = Ocb3::<Aes128, U16>::new(&key);
/// ```
///
/// ```rust,compile_fail
/// # use aes::Aes128;
/// # use ocb3::{aead::{consts::{U12, U0}, KeyInit}, Ocb3};
/// # let key = [42; 16].into();
/// // Invalid tag size equal to 0 bytes
/// let cipher = Ocb3::<Aes128, U12, U0>::new(&key);
/// ```
///
/// ```rust,compile_fail
/// # use aes::Aes128;
/// # use ocb3::{aead::{consts::{U12, U20}, KeyInit}, Ocb3};
/// # let key = [42; 16].into();
/// // Invalid tag size equal to 20 bytes
/// let cipher = Ocb3::<Aes128, U12, U20>::new(&key);
/// ```
#[derive(Clone)]
pub struct Ocb3<Cipher, NonceSize = U12, TagSize = U16>
where
NonceSize: ArrayLength<u8> + IsGreaterOrEqual<U6> + IsLessOrEqual<U15>,
TagSize: ArrayLength<u8> + IsGreater<U0> + IsLessOrEqual<U16>,
TagSize: ArrayLength<u8> + NonZero + IsLessOrEqual<U16>,
GrEq<NonceSize, U6>: NonZero,
LeEq<NonceSize, U15>: NonZero,
LeEq<TagSize, U16>: NonZero,
{
cipher: Cipher,
nonce_size: PhantomData<NonceSize>,
Expand All @@ -87,17 +124,23 @@ type Sum = GenericArray<u8, SumSize>;
impl<Cipher, NonceSize, TagSize> KeySizeUser for Ocb3<Cipher, NonceSize, TagSize>
where
Cipher: KeySizeUser,
TagSize: ArrayLength<u8> + IsGreater<U0> + IsLessOrEqual<U16>,
NonceSize: ArrayLength<u8> + IsGreaterOrEqual<U6> + IsLessOrEqual<U15>,
TagSize: ArrayLength<u8> + NonZero + IsLessOrEqual<U16>,
GrEq<NonceSize, U6>: NonZero,
LeEq<NonceSize, U15>: NonZero,
LeEq<TagSize, U16>: NonZero,
{
type KeySize = Cipher::KeySize;
}

impl<Cipher, NonceSize, TagSize> KeyInit for Ocb3<Cipher, NonceSize, TagSize>
where
Cipher: BlockSizeUser<BlockSize = U16> + BlockEncrypt + KeyInit + BlockDecrypt,
TagSize: ArrayLength<u8> + IsGreater<U0> + IsLessOrEqual<U16>,
NonceSize: ArrayLength<u8> + IsGreaterOrEqual<U6> + IsLessOrEqual<U15>,
TagSize: ArrayLength<u8> + NonZero + IsLessOrEqual<U16>,
GrEq<NonceSize, U6>: NonZero,
LeEq<NonceSize, U15>: NonZero,
LeEq<TagSize, U16>: NonZero,
{
fn new(key: &aead::Key<Self>) -> Self {
Cipher::new(key).into()
Expand All @@ -107,7 +150,10 @@ where
impl<Cipher, NonceSize, TagSize> AeadCore for Ocb3<Cipher, NonceSize, TagSize>
where
NonceSize: ArrayLength<u8> + IsGreaterOrEqual<U6> + IsLessOrEqual<U15>,
TagSize: ArrayLength<u8> + IsGreater<U0> + IsLessOrEqual<U16>,
TagSize: ArrayLength<u8> + NonZero + IsLessOrEqual<U16>,
GrEq<NonceSize, U6>: NonZero,
LeEq<NonceSize, U15>: NonZero,
LeEq<TagSize, U16>: NonZero,
{
type NonceSize = NonceSize;
type TagSize = TagSize;
Expand All @@ -117,8 +163,11 @@ where
impl<Cipher, NonceSize, TagSize> From<Cipher> for Ocb3<Cipher, NonceSize, TagSize>
where
Cipher: BlockSizeUser<BlockSize = U16> + BlockEncrypt + BlockDecrypt,
TagSize: ArrayLength<u8> + IsGreater<U0> + IsLessOrEqual<U16>,
NonceSize: ArrayLength<u8> + IsGreaterOrEqual<U6> + IsLessOrEqual<U15>,
TagSize: ArrayLength<u8> + NonZero + IsLessOrEqual<U16>,
GrEq<NonceSize, U6>: NonZero,
LeEq<NonceSize, U15>: NonZero,
LeEq<TagSize, U16>: NonZero,
{
fn from(cipher: Cipher) -> Self {
let (ll_star, ll_dollar, ll) = key_dependent_variables(&cipher);
Expand Down Expand Up @@ -157,8 +206,11 @@ fn key_dependent_variables<Cipher: BlockSizeUser<BlockSize = U16> + BlockEncrypt
impl<Cipher, NonceSize, TagSize> AeadInPlace for Ocb3<Cipher, NonceSize, TagSize>
where
Cipher: BlockSizeUser<BlockSize = U16> + BlockEncrypt + BlockDecrypt,
TagSize: ArrayLength<u8> + IsGreater<U0> + IsLessOrEqual<U16>,
NonceSize: ArrayLength<u8> + IsGreaterOrEqual<U6> + IsLessOrEqual<U15>,
TagSize: ArrayLength<u8> + NonZero + IsLessOrEqual<U16>,
GrEq<NonceSize, U6>: NonZero,
LeEq<NonceSize, U15>: NonZero,
LeEq<TagSize, U16>: NonZero,
{
fn encrypt_in_place_detached(
&self,
Expand Down Expand Up @@ -239,8 +291,11 @@ where
impl<Cipher, NonceSize, TagSize> Ocb3<Cipher, NonceSize, TagSize>
where
Cipher: BlockSizeUser<BlockSize = U16> + BlockEncrypt + BlockDecrypt,
TagSize: ArrayLength<u8> + IsGreater<U0> + IsLessOrEqual<U16>,
NonceSize: ArrayLength<u8> + IsGreaterOrEqual<U6> + IsLessOrEqual<U15>,
TagSize: ArrayLength<u8> + NonZero + IsLessOrEqual<U16>,
GrEq<NonceSize, U6>: NonZero,
LeEq<NonceSize, U15>: NonZero,
LeEq<TagSize, U16>: NonZero,
{
/// Decrypts in place and returns expected tag.
pub(crate) fn decrypt_in_place_return_tag(
Expand Down Expand Up @@ -447,8 +502,11 @@ fn initial_offset<
impl<Cipher, NonceSize, TagSize> Ocb3<Cipher, NonceSize, TagSize>
where
Cipher: BlockSizeUser<BlockSize = U16> + BlockEncrypt,
TagSize: ArrayLength<u8> + IsGreater<U0> + IsLessOrEqual<U16>,
NonceSize: ArrayLength<u8> + IsGreaterOrEqual<U6> + IsLessOrEqual<U15>,
TagSize: ArrayLength<u8> + NonZero + IsLessOrEqual<U16>,
GrEq<NonceSize, U6>: NonZero,
LeEq<NonceSize, U15>: NonZero,
LeEq<TagSize, U16>: NonZero,
{
/// Computes HASH function defined in https://www.rfc-editor.org/rfc/rfc7253.html#section-4.1
fn hash(&self, associated_data: &[u8]) -> Sum {
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