eax: use 4-byte nonce instead of block size

This is a hack until RustCrypto#239 is fixed.

eax/src/lib.rs

@@ -83,7 +83,7 @@ pub use cipher;
 
 use cipher::{
     block::{Block, BlockCipher, Key, NewBlockCipher},
-    consts::{U0, U16},
+    consts::{U0, U4, U16},
     generic_array::{functional::FunctionalSequence, ArrayLength, GenericArray},
     stream::{FromBlockCipher, SyncStreamCipher},
 };
@@ -137,7 +137,7 @@ where
     Cipher: BlockCipher<BlockSize = U16> + NewBlockCipher + Clone,
     Cipher::ParBlocks: ArrayLength<Block<Cipher>>,
 {
-    type NonceSize = Cipher::BlockSize;
+    type NonceSize = U4;
     type TagSize = <Cmac<Cipher> as Mac>::OutputSize;
     type CiphertextOverhead = U0;
 

eax/src/online.rs

@@ -60,6 +60,7 @@
 use crate::*;
 
 use core::marker::PhantomData;
+use cipher::consts::U4;
 
 pub use Eax as EaxOnline;
 
@@ -160,7 +161,7 @@ where
 {
     /// 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<U4>) -> Self {
         let imp = EaxImpl::<Cipher>::with_key_and_nonce(key, nonce);
 
         Self {
@@ -261,7 +262,7 @@ where
     Cipher: BlockCipher<BlockSize = U16> + NewBlockCipher + Clone,
     Cipher::ParBlocks: ArrayLength<Block<Cipher>>,
 {
-    nonce: Nonce<Cipher::BlockSize>,
+    nonce: Nonce<U4>,
     data: Cmac<Cipher>,
     message: Cmac<Cipher>,
     ctr: ctr::Ctr128<Cipher>,
@@ -277,7 +278,7 @@ 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: &Nonce<U4>) -> Self {
         let prepend_cmac = |key, init_val, data| {
             let mut cmac = Cmac::<Cipher>::new(key);
             cmac.update(&[0; 15]);
@@ -400,7 +401,7 @@ mod test_impl {
         Cipher: BlockCipher<BlockSize = U16> + NewBlockCipher + Clone,
         Cipher::ParBlocks: ArrayLength<Block<Cipher>>,
     {
-        type NonceSize = Cipher::BlockSize;
+        type NonceSize = U4;
         type TagSize = <Cmac<Cipher> as Mac>::OutputSize;
         type CiphertextOverhead = U0;