eax: support nonces of any length

eax/src/lib.rs

@@ -125,6 +125,29 @@
 //! assert_eq!(buffer.as_ref(), b"plaintext message");
 //! # }
 //! ```
+//!
+//! ## Custom Nonce Length
+//!
+//! EAX accepts nonces of any length. The nonce is 16 bytes long by default;
+//! the third generic argument of `Eax` sets another length:
+//!
+//! ```
+//! # #[cfg(feature = "alloc")]
+//! # {
+//! use aes::Aes128;
+//! use eax::Eax;
+//! use eax::aead::{Aead, KeyInit, array::Array};
+//! use eax::aead::consts::{U12, U16};
+//!
+//! let key = Array::from_slice(b"very secret key.");
+//! let cipher = Eax::<Aes128, U16, U12>::new(key);
+//!
+//! let nonce = Array::from_slice(b"unique nonce"); // 96-bits; unique per message
+//! let ciphertext = cipher.encrypt(nonce, b"plaintext message".as_ref()).unwrap();
+//! let plaintext = cipher.decrypt(nonce, ciphertext.as_ref()).unwrap();
+//! assert_eq!(&plaintext, b"plaintext message");
+//! # }
+//! ```
 
 mod traits;
 
@@ -133,7 +156,9 @@ pub use cipher;
 
 use aead::{TagPosition, inout::InOutBuf};
 use cipher::{
-    BlockCipherEncrypt, BlockSizeUser, InnerIvInit, StreamCipherCore, array::Array, consts::U16,
+    BlockCipherEncrypt, BlockSizeUser, InnerIvInit, StreamCipherCore,
+    array::{Array, ArraySize},
+    consts::U16,
 };
 use cmac::{Cmac, Mac, digest::Output};
 use core::{fmt, marker::PhantomData};
@@ -167,52 +192,60 @@ type Ctr128BE<C> = ctr::CtrCore<C, ctr::flavors::Ctr128BE>;
 /// ## Type parameters
 /// - `Cipher`: block cipher.
 /// - `M`: size of MAC tag, valid values: up to `U16`.
+/// - `NonceSize`: size of nonce, any length (default `U16`).
 #[derive(Clone)]
-pub struct Eax<Cipher, M = U16>
+pub struct Eax<Cipher, M = U16, NonceSize = U16>
 where
     Cipher: BlockSizeUser<BlockSize = U16> + BlockCipherEncrypt + Clone + KeyInit,
     M: TagSize,
+    NonceSize: ArraySize,
 {
     /// Encryption key
     key: Key<Cipher>,
     _tag_size: PhantomData<M>,
+    _nonce_size: PhantomData<NonceSize>,
 }
 
-impl<Cipher, M> KeySizeUser for Eax<Cipher, M>
+impl<Cipher, M, NonceSize> KeySizeUser for Eax<Cipher, M, NonceSize>
 where
     Cipher: BlockSizeUser<BlockSize = U16> + BlockCipherEncrypt + Clone + KeyInit,
     M: TagSize,
+    NonceSize: ArraySize,
 {
     type KeySize = Cipher::KeySize;
 }
 
-impl<Cipher, M> KeyInit for Eax<Cipher, M>
+impl<Cipher, M, NonceSize> KeyInit for Eax<Cipher, M, NonceSize>
 where
     Cipher: BlockSizeUser<BlockSize = U16> + BlockCipherEncrypt + Clone + KeyInit,
     M: TagSize,
+    NonceSize: ArraySize,
 {
     fn new(key: &Key<Cipher>) -> Self {
         Self {
             key: key.clone(),
             _tag_size: PhantomData,
+            _nonce_size: PhantomData,
         }
     }
 }
 
-impl<Cipher, M> AeadCore for Eax<Cipher, M>
+impl<Cipher, M, NonceSize> AeadCore for Eax<Cipher, M, NonceSize>
 where
     Cipher: BlockSizeUser<BlockSize = U16> + BlockCipherEncrypt + Clone + KeyInit,
     M: TagSize,
+    NonceSize: ArraySize,
 {
-    type NonceSize = Cipher::BlockSize;
+    type NonceSize = NonceSize;
     type TagSize = M;
     const TAG_POSITION: TagPosition = TagPosition::Postfix;
 }
 
-impl<Cipher, M> AeadInOut for Eax<Cipher, M>
+impl<Cipher, M, NonceSize> AeadInOut for Eax<Cipher, M, NonceSize>
 where
     Cipher: BlockSizeUser<BlockSize = U16> + BlockCipherEncrypt + Clone + KeyInit,
     M: TagSize,
+    NonceSize: ArraySize,
 {
     fn encrypt_inout_detached(
         &self,
@@ -285,20 +318,22 @@ where
     }
 }
 
-impl<Cipher, M> fmt::Debug for Eax<Cipher, M>
+impl<Cipher, M, NonceSize> fmt::Debug for Eax<Cipher, M, NonceSize>
 where
     Cipher: BlockSizeUser<BlockSize = U16> + BlockCipherEncrypt + Clone + KeyInit,
     M: TagSize,
+    NonceSize: ArraySize,
 {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
         f.debug_struct("Eax").finish_non_exhaustive()
     }
 }
 
-impl<Cipher, M> Eax<Cipher, M>
+impl<Cipher, M, NonceSize> Eax<Cipher, M, NonceSize>
 where
     Cipher: BlockSizeUser<BlockSize = U16> + BlockCipherEncrypt + Clone + KeyInit,
     M: TagSize,
+    NonceSize: ArraySize,
 {
     /// CMAC/OMAC1
     ///

eax/src/online.rs

@@ -60,7 +60,8 @@
 use crate::{Cmac, Error, Nonce, Tag, TagSize};
 use aead::consts::U16;
 use cipher::{
-    BlockCipherEncrypt, BlockSizeUser, Key, KeyInit, KeyIvInit, StreamCipher, array::Array,
+    BlockCipherEncrypt, BlockSizeUser, Key, KeyInit, KeyIvInit, StreamCipher,
+    array::{Array, ArraySize},
     typenum::Unsigned,
 };
 use cmac::Mac;
@@ -150,31 +151,35 @@ impl CipherOp for Decrypt {}
 /// [`Eax`]: ../struct.Eax.html
 /// [`Decrypt`]: struct.Decrypt.html
 /// [`finish`]: #method.finish
-pub struct Eax<Cipher, Op, M = U16>
+pub struct Eax<Cipher, Op, M = U16, NonceSize = U16>
 where
     Cipher: BlockSizeUser<BlockSize = U16> + BlockCipherEncrypt + Clone + KeyInit,
     Op: CipherOp,
     M: TagSize,
+    NonceSize: ArraySize,
 {
     imp: EaxImpl<Cipher, M>,
     /// Denotes whether this stream is used for encryption or decryption.
     marker: PhantomData<Op>,
+    _nonce_size: PhantomData<NonceSize>,
 }
 
-impl<Cipher, Op, M> Eax<Cipher, Op, M>
+impl<Cipher, Op, M, NonceSize> Eax<Cipher, Op, M, NonceSize>
 where
     Cipher: BlockSizeUser<BlockSize = U16> + BlockCipherEncrypt + Clone + KeyInit,
     Op: CipherOp,
     M: TagSize,
+    NonceSize: ArraySize,
 {
     /// Creates a stateful EAX instance that is capable of processing both
     /// the associated data and the plaintext in an "on-line" fashion.
-    pub fn with_key_and_nonce(key: &Key<Cipher>, nonce: &Nonce<Cipher::BlockSize>) -> Self {
+    pub fn with_key_and_nonce(key: &Key<Cipher>, nonce: &Nonce<NonceSize>) -> Self {
         let imp = EaxImpl::<Cipher, M>::with_key_and_nonce(key, nonce);
 
         Self {
             imp,
             marker: PhantomData,
+            _nonce_size: PhantomData,
         }
     }
 
@@ -196,10 +201,11 @@ where
     }
 }
 
-impl<Cipher, M> Eax<Cipher, Encrypt, M>
+impl<Cipher, M, NonceSize> Eax<Cipher, Encrypt, M, NonceSize>
 where
     Cipher: BlockSizeUser<BlockSize = U16> + BlockCipherEncrypt + Clone + KeyInit,
     M: TagSize,
+    NonceSize: ArraySize,
 {
     /// Applies encryption to the plaintext.
     #[inline]
@@ -217,10 +223,11 @@ where
     }
 }
 
-impl<Cipher, M> Eax<Cipher, Decrypt, M>
+impl<Cipher, M, NonceSize> Eax<Cipher, Decrypt, M, NonceSize>
 where
     Cipher: BlockSizeUser<BlockSize = U16> + BlockCipherEncrypt + Clone + KeyInit,
     M: TagSize,
+    NonceSize: ArraySize,
 {
     /// Applies decryption to the ciphertext **without** verifying the
     /// authenticity of decrypted message.
@@ -267,11 +274,12 @@ where
     }
 }
 
-impl<Cipher, Op, M> fmt::Debug for Eax<Cipher, Op, M>
+impl<Cipher, Op, M, NonceSize> fmt::Debug for Eax<Cipher, Op, M, NonceSize>
 where
     Cipher: BlockSizeUser<BlockSize = U16> + BlockCipherEncrypt + Clone + KeyInit,
     Op: CipherOp,
     M: TagSize,
+    NonceSize: ArraySize,
 {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
         f.debug_struct("Eax").finish_non_exhaustive()
@@ -302,7 +310,7 @@ where
 {
     /// Creates a stateful EAX instance that is capable of processing both
     /// the associated data and the plaintext in an "on-line" fashion.
-    fn with_key_and_nonce(key: &Key<Cipher>, nonce: &Nonce<Cipher::BlockSize>) -> Self {
+    fn with_key_and_nonce(key: &Key<Cipher>, nonce: &[u8]) -> Self {
         let prepend_cmac = |key, init_val, data| {
             let mut cmac = <Cmac<Cipher> as KeyInit>::new(key);
             cmac.update(&[0; 15]);

eax/tests/wycheproof.rs

@@ -1,13 +1,86 @@
-//! Test vectors from Wycheproof (`aes_eax_test.json`): the groups with a
-//! 128-bit nonce and a 128-bit tag, for AES-128, AES-192 and AES-256.
+//! Test vectors from Wycheproof (`aes_eax_test.json`) with a 128-bit tag, for
+//! AES-128, AES-192 and AES-256.
 #![cfg(feature = "alloc")]
 
+use aead::{
+    array::ArraySize,
+    consts::{U0, U4, U8, U12, U16, U20, U32, U64, U128, U257},
+    dev::{TestVector, blobby, pass_test},
+};
 use aes::{Aes128, Aes192, Aes256};
-use eax::Eax;
+use eax::{
+    Eax, KeyInit, Tag,
+    cipher::{BlockCipherEncrypt, BlockSizeUser},
+    online::{Decrypt, Eax as EaxOnline, Encrypt},
+};
 
+// The groups with a 128-bit nonce.
 aead::new_pass_test!(aes128_pass, "wycheproof-128_pass", Eax<Aes128>);
 aead::new_fail_test!(aes128_fail, "wycheproof-128_fail", Eax<Aes128>);
 aead::new_pass_test!(aes192_pass, "wycheproof-192_pass", Eax<Aes192>);
 aead::new_fail_test!(aes192_fail, "wycheproof-192_fail", Eax<Aes192>);
 aead::new_pass_test!(aes256_pass, "wycheproof-256_pass", Eax<Aes256>);
 aead::new_fail_test!(aes256_fail, "wycheproof-256_fail", Eax<Aes256>);
+
+/// Checks a vector with both `Eax` and `online::Eax` using an `N`-byte nonce.
+fn nonce_len_test<C, N>(i: usize, tv: &TestVector)
+where
+    C: BlockSizeUser<BlockSize = U16> + BlockCipherEncrypt + Clone + KeyInit,
+    N: ArraySize,
+{
+    if let Err(reason) = pass_test::<Eax<C, U16, N>>(tv) {
+        panic!("\nFailed test #{i}\nreason:\t{reason:?}\ntest vector:\t{tv:?}\n");
+    }
+
+    let key = tv.key.try_into().expect("wrong key size");
+    let nonce = tv.nonce.try_into().expect("wrong nonce size");
+    let (ct, tag) = tv.ciphertext.split_at(tv.plaintext.len());
+    let tag: &Tag<U16> = tag.try_into().expect("wrong tag size");
+
+    let mut buf = tv.plaintext.to_vec();
+    let mut cipher = EaxOnline::<C, Encrypt, U16, N>::with_key_and_nonce(key, nonce);
+    cipher.update_assoc(tv.aad);
+    cipher.encrypt(&mut buf);
+    assert_eq!(buf, ct, "online encryption, test #{i}");
+    assert_eq!(&cipher.finish(), tag, "online tag, test #{i}");
+
+    let mut cipher = EaxOnline::<C, Decrypt, U16, N>::with_key_and_nonce(key, nonce);
+    cipher.update_assoc(tv.aad);
+    cipher.decrypt_unauthenticated_hazmat(&mut buf);
+    assert_eq!(buf, tv.plaintext, "online decryption, test #{i}");
+    assert!(cipher.finish(tag).is_ok(), "online tag check, test #{i}");
+}
+
+/// The groups with a nonce that is not 128 bits long (0 to 257 bytes).
+macro_rules! new_nonce_len_test {
+    ($name:ident, $test_name:expr, $cipher:ty) => {
+        #[test]
+        fn $name() {
+            blobby::parse_into_structs!(
+                include_bytes!(concat!("data/", $test_name, ".blb"));
+                static TEST_VECTORS: &[
+                    TestVector { key, nonce, aad, plaintext, ciphertext }
+                ];
+            );
+
+            for (i, tv) in TEST_VECTORS.iter().enumerate() {
+                match tv.nonce.len() {
+                    0 => nonce_len_test::<$cipher, U0>(i, tv),
+                    4 => nonce_len_test::<$cipher, U4>(i, tv),
+                    8 => nonce_len_test::<$cipher, U8>(i, tv),
+                    12 => nonce_len_test::<$cipher, U12>(i, tv),
+                    20 => nonce_len_test::<$cipher, U20>(i, tv),
+                    32 => nonce_len_test::<$cipher, U32>(i, tv),
+                    64 => nonce_len_test::<$cipher, U64>(i, tv),
+                    128 => nonce_len_test::<$cipher, U128>(i, tv),
+                    257 => nonce_len_test::<$cipher, U257>(i, tv),
+                    n => panic!("no test for a {n}-byte nonce"),
+                }
+            }
+        }
+    };
+}
+
+new_nonce_len_test!(aes128_nonce_len, "wycheproof-128_nonce-len", Aes128);
+new_nonce_len_test!(aes192_nonce_len, "wycheproof-192_nonce-len", Aes192);
+new_nonce_len_test!(aes256_nonce_len, "wycheproof-256_nonce-len", Aes256);