stream-cipher: add FromBlockCipher trait (fixes RustCrypto#32) (RustC…

…rypto#164)

Support for instantiating a stream cipher from a block cipher

.github/workflows/stream-cipher.yml

@@ -51,6 +51,7 @@ jobs:
         toolchain: ${{ matrix.rust }}
     - run: cargo check --all-features
     - run: cargo test --release
+    - run: cargo test --features block-cipher
     - run: cargo test --features dev --release
     - run: cargo test --features std --release
     - run: cargo test --all-features --release

stream-cipher/Cargo.toml

@@ -15,9 +15,15 @@ categories = ["cryptography", "no-std"]
 generic-array = "0.14"
 blobby = { version = "0.1", optional = true }
 
+[dependencies.block-cipher]
+version = "= 0.7.0-pre"
+optional = true
+path = "../block-cipher"
+
 [features]
 std = []
 dev = ["blobby"]
 
 [package.metadata.docs.rs]
-features = [ "std" ]
+all-features = true
+rustdoc-args = ["--cfg", "docsrs"]

stream-cipher/src/dev.rs

@@ -4,6 +4,7 @@ pub use blobby;
 
 /// Test core functionality of synchronous stream cipher
 #[macro_export]
+#[cfg_attr(docsrs, doc(cfg(feature = "dev")))]
 macro_rules! new_sync_test {
     ($name:ident, $cipher:ty, $test_name:expr) => {
         #[test]
@@ -43,6 +44,7 @@ macro_rules! new_sync_test {
 
 /// Test stream synchronous stream cipher seeking capabilities
 #[macro_export]
+#[cfg_attr(docsrs, doc(cfg(feature = "dev")))]
 macro_rules! new_seek_test {
     ($name:ident, $cipher:ty, $test_name:expr) => {
         #[test]
@@ -85,6 +87,7 @@ macro_rules! new_seek_test {
 
 /// Test core functionality of asynchronous stream cipher
 #[macro_export]
+#[cfg_attr(docsrs, doc(cfg(feature = "dev")))]
 macro_rules! new_async_test {
     ($name:ident, $test_name:expr, $cipher:ty) => {
         #[test]
@@ -149,6 +152,7 @@ macro_rules! new_async_test {
 
 /// Create synchronous stream cipher benchmarks
 #[macro_export]
+#[cfg_attr(docsrs, doc(cfg(feature = "dev")))]
 macro_rules! bench_sync {
     ($name:ident, $cipher:path, $data_len:expr) => {
         #[bench]
@@ -187,6 +191,7 @@ macro_rules! bench_sync {
 
 /// Create synchronous stream cipher benchmarks
 #[macro_export]
+#[cfg_attr(docsrs, doc(cfg(feature = "dev")))]
 macro_rules! bench_async {
     ($enc_name:ident, $dec_name:ident, $cipher:path, $data_len:expr) => {
         #[bench]

stream-cipher/src/lib.rs

@@ -5,6 +5,7 @@
 //! for ciphers implementation.
 
 #![no_std]
+#![cfg_attr(docsrs, feature(doc_cfg))]
 #![doc(html_logo_url = "https://raw.githubusercontent.com/RustCrypto/meta/master/logo_small.png")]
 #![forbid(unsafe_code)]
 #![warn(missing_docs, rust_2018_idioms)]
@@ -13,6 +14,7 @@
 extern crate std;
 
 #[cfg(feature = "dev")]
+#[cfg_attr(docsrs, doc(cfg(feature = "dev")))]
 pub mod dev;
 
 mod errors;
@@ -23,6 +25,9 @@ pub use generic_array::{self, typenum::consts};
 use generic_array::typenum::Unsigned;
 use generic_array::{ArrayLength, GenericArray};
 
+#[cfg(feature = "block-cipher")]
+use block_cipher::{BlockCipher, NewBlockCipher};
+
 /// Stream cipher creation trait.
 ///
 /// It can be used for creation of synchronous and asynchronous ciphers.
@@ -112,3 +117,34 @@ impl<C: SyncStreamCipher> StreamCipher for C {
         SyncStreamCipher::apply_keystream(self, data);
     }
 }
+
+/// Trait for initializing a stream cipher from a block cipher
+#[cfg(feature = "block-cipher")]
+#[cfg_attr(docsrs, doc(cfg(feature = "block-cipher")))]
+pub trait FromBlockCipher {
+    /// Block cipher
+    type BlockCipher: BlockCipher + NewBlockCipher;
+
+    /// Instantiate a stream cipher from a block cipher
+    // TODO(tarcieri): add associated type for NonceSize?
+    fn from_block_cipher(
+        cipher: Self::BlockCipher,
+        nonce: &block_cipher::Block<Self::BlockCipher>,
+    ) -> Self;
+}
+
+#[cfg(feature = "block-cipher")]
+impl<C> NewStreamCipher for C
+where
+    C: FromBlockCipher,
+{
+    type KeySize = <<Self as FromBlockCipher>::BlockCipher as NewBlockCipher>::KeySize;
+    type NonceSize = <<Self as FromBlockCipher>::BlockCipher as BlockCipher>::BlockSize;
+
+    fn new(key: &GenericArray<u8, Self::KeySize>, nonce: &GenericArray<u8, Self::NonceSize>) -> C {
+        C::from_block_cipher(
+            <<Self as FromBlockCipher>::BlockCipher as NewBlockCipher>::new(key),
+            nonce,
+        )
+    }
+}