From e72b5441095e16754fa0ee899c5c1de0ee70b0dd Mon Sep 17 00:00:00 2001
From: Tony Arcieri <bascule@gmail.com>
Date: Sat, 19 Mar 2022 11:28:28 -0600
Subject: [PATCH] ctr: use `BlockEncrypt` instead of `BlockEncryptMut`

As far as I can tell this is just a mistake: the only state in CTR mode
is the counter, and there is no reason to mandate some sort of stateful
block cipher as part of the bounds.

A `BlockCipherMut` bound is a significant impediment to upgrading the
AEAD crates, which all impl `AeadInPlace` instead of `AeadMutInPlace`,
store block cipher instances (which avoids re-expanding keys),
and need to be able to share non-mutable references to those block
cipher instances.
---
 ctr/src/ctr_core.rs | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/ctr/src/ctr_core.rs b/ctr/src/ctr_core.rs
index 7868f5b..a69f1a5 100644
--- a/ctr/src/ctr_core.rs
+++ b/ctr/src/ctr_core.rs
@@ -1,7 +1,7 @@
 use crate::{backend::Closure, CtrFlavor};
 use cipher::{
     crypto_common::{InnerUser, IvSizeUser},
-    AlgorithmName, BlockCipher, BlockEncryptMut, BlockSizeUser, InnerIvInit, Iv, IvState,
+    AlgorithmName, BlockCipher, BlockEncrypt, BlockSizeUser, InnerIvInit, Iv, IvState,
     StreamCipherCore, StreamCipherSeekCore, StreamClosure,
 };
 use core::fmt;
@@ -13,7 +13,7 @@ use cipher::zeroize::ZeroizeOnDrop;
 #[derive(Clone)]
 pub struct CtrCore<C, F>
 where
-    C: BlockEncryptMut + BlockCipher,
+    C: BlockEncrypt + BlockCipher,
     F: CtrFlavor<C::BlockSize>,
 {
     cipher: C,
@@ -22,7 +22,7 @@ where
 
 impl<C, F> BlockSizeUser for CtrCore<C, F>
 where
-    C: BlockEncryptMut + BlockCipher,
+    C: BlockEncrypt + BlockCipher,
     F: CtrFlavor<C::BlockSize>,
 {
     type BlockSize = C::BlockSize;
@@ -30,7 +30,7 @@ where
 
 impl<C, F> StreamCipherCore for CtrCore<C, F>
 where
-    C: BlockEncryptMut + BlockCipher,
+    C: BlockEncrypt + BlockCipher,
     F: CtrFlavor<C::BlockSize>,
 {
     #[inline]
@@ -41,13 +41,13 @@ where
     #[inline]
     fn process_with_backend(&mut self, f: impl StreamClosure<BlockSize = Self::BlockSize>) {
         let Self { cipher, ctr_nonce } = self;
-        cipher.encrypt_with_backend_mut(Closure::<F, _, _> { ctr_nonce, f });
+        cipher.encrypt_with_backend(Closure::<F, _, _> { ctr_nonce, f });
     }
 }
 
 impl<C, F> StreamCipherSeekCore for CtrCore<C, F>
 where
-    C: BlockEncryptMut + BlockCipher,
+    C: BlockEncrypt + BlockCipher,
     F: CtrFlavor<C::BlockSize>,
 {
     type Counter = F::Backend;
@@ -65,7 +65,7 @@ where
 
 impl<C, F> InnerUser for CtrCore<C, F>
 where
-    C: BlockEncryptMut + BlockCipher,
+    C: BlockEncrypt + BlockCipher,
     F: CtrFlavor<C::BlockSize>,
 {
     type Inner = C;
@@ -73,7 +73,7 @@ where
 
 impl<C, F> IvSizeUser for CtrCore<C, F>
 where
-    C: BlockEncryptMut + BlockCipher,
+    C: BlockEncrypt + BlockCipher,
     F: CtrFlavor<C::BlockSize>,
 {
     type IvSize = C::BlockSize;
@@ -81,7 +81,7 @@ where
 
 impl<C, F> InnerIvInit for CtrCore<C, F>
 where
-    C: BlockEncryptMut + BlockCipher,
+    C: BlockEncrypt + BlockCipher,
     F: CtrFlavor<C::BlockSize>,
 {
     #[inline]
@@ -95,7 +95,7 @@ where
 
 impl<C, F> IvState for CtrCore<C, F>
 where
-    C: BlockEncryptMut + BlockCipher,
+    C: BlockEncrypt + BlockCipher,
     F: CtrFlavor<C::BlockSize>,
 {
     #[inline]
@@ -106,7 +106,7 @@ where
 
 impl<C, F> AlgorithmName for CtrCore<C, F>
 where
-    C: BlockEncryptMut + BlockCipher + AlgorithmName,
+    C: BlockEncrypt + BlockCipher + AlgorithmName,
     F: CtrFlavor<C::BlockSize>,
 {
     fn write_alg_name(f: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -120,7 +120,7 @@ where
 
 impl<C, F> fmt::Debug for CtrCore<C, F>
 where
-    C: BlockEncryptMut + BlockCipher + AlgorithmName,
+    C: BlockEncrypt + BlockCipher + AlgorithmName,
     F: CtrFlavor<C::BlockSize>,
 {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -136,7 +136,7 @@ where
 #[cfg_attr(docsrs, doc(cfg(feature = "zeroize")))]
 impl<C, F> ZeroizeOnDrop for CtrCore<C, F>
 where
-    C: BlockEncryptMut + BlockCipher + ZeroizeOnDrop,
+    C: BlockEncrypt + BlockCipher + ZeroizeOnDrop,
     F: CtrFlavor<C::BlockSize>,
     F::CtrNonce: ZeroizeOnDrop,
 {