no_std support

Added basic no_std support by switching to `core` and `alloc`
libraries wherever possible. Restructured features in Cargo.toml
to allow for customized setups with or without the standard library.

Cargo.toml

@@ -15,20 +15,45 @@ edition = "2021"
 # This is slightly mumbo-jumboey, but in short:
 # Features with a -resolver suffix simply enables the existence of a specific resolver,
 # and -accelerated suffix means that this resolver will be the default used by the Builder.
+#
+# If default features are disabled and default-resolver is used, required crypto primitives
+# must be enabled individually.
 [features]
-default = ["default-resolver"]
-default-resolver = ["aes-gcm", "chacha20poly1305", "blake2", "sha2", "curve25519-dalek"]
+default = ["default-resolver", "default-resolver-crypto", "std"]
+default-resolver = []
+default-resolver-crypto = ["use-aes-gcm", "use-chacha20poly1305", "use-blake2", "use-sha2", "use-curve25519-dalek"]
 nightly = ["blake2/simd_opt", "subtle/nightly"]
-ring-resolver = ["ring"]
-ring-accelerated = ["ring-resolver", "default-resolver"]
-libsodium-resolver = ["sodiumoxide", "byteorder"]
-libsodium-accelerated = ["libsodium-resolver", "default-resolver"]
+ring-resolver = ["ring", "std"]
+ring-accelerated = ["ring-resolver", "default-resolver", "std"]
+libsodium-resolver = ["sodiumoxide", "byteorder", "std"]
+libsodium-accelerated = ["libsodium-resolver", "default-resolver", "std"]
 vector-tests = []
 hfs = []
-pqclean_kyber1024 = ["pqcrypto-kyber", "pqcrypto-traits", "hfs", "default-resolver"]
-xchachapoly = ["chacha20poly1305", "default-resolver"]
 risky-raw-split = []
 
+# Backwards-compatibility aliases
+pqclean_kyber1024 = ["use-pqcrypto-kyber1024"]
+xchachapoly = ["use-xchacha20poly1305"]
+
+# Enable std features on dependencies if possible.
+std = [
+    "rand_core/std",
+    "subtle/std",
+    "ring/std",
+    "blake2/std",
+    "sha2/std",
+    "byteorder/std",
+    ]
+
+# Crypto primitives for default-resolver.
+use-curve25519-dalek = ["curve25519-dalek", "default-resolver"]
+use-chacha20poly1305 = ["chacha20poly1305", "default-resolver"]
+use-xchacha20poly1305 = ["chacha20poly1305", "default-resolver"]
+use-blake2 = ["blake2", "default-resolver"]
+use-sha2 = ["sha2", "default-resolver"]
+use-aes-gcm = ["aes-gcm", "default-resolver"]
+use-pqcrypto-kyber1024 = ["pqcrypto-kyber", "pqcrypto-traits", "hfs", "default-resolver"]
+
 [[bench]]
 name = "benches"
 harness = false
@@ -37,24 +62,24 @@ harness = false
 travis-ci = { repository = "mcginty/snow", branch = "master" }
 
 [dependencies]
-rand_core = { version = "0.6", features = ["std", "getrandom"] }
-subtle = "2.4"
+rand_core = { version = "0.6", default-features = false, features = ["getrandom"] }
+subtle = { version = "2.4", default-features = false }
 
 # default crypto provider
-aes-gcm = { version = "0.10", optional = true }
-chacha20poly1305 = { version = "0.10", optional = true }
-blake2 = { version = "0.10", optional = true }
-sha2 = { version = "0.10", optional = true }
-curve25519-dalek = { version = "4", optional = true }
+aes-gcm = { version = "0.10", optional = true, default-features = false, features = ["aes"] }
+chacha20poly1305 = { version = "0.10", optional = true, default-features = false }
+blake2 = { version = "0.10", optional = true, default-features = false }
+sha2 = { version = "0.10", optional = true, default-features = false }
+curve25519-dalek = { version = "4", optional = true, default-features = false }
 
 pqcrypto-kyber = { version = "0.8", optional = true }
 pqcrypto-traits = { version = "0.3", optional = true }
 
 # ring crypto provider
-ring = { version = "0.17", optional = true, features = ["std"] }
+ring = { version = "0.17", optional = true }
 # libsodium crypto provider
-sodiumoxide = { version = "0.2", optional = true }
-byteorder = { version = "1.4", optional = true }
+sodiumoxide = { version = "0.2", optional = true, default-features = false }
+byteorder = { version = "1.4", optional = true, default-features = false }
 
 [dev-dependencies]
 criterion = "0.5"

README.md

@@ -77,6 +77,69 @@ crypto implementations when available.
 |    BLAKE2s |    ✔    |      |
 |    BLAKE2b |    ✔    |      |
 
+## `no_std` support and feature selection
+
+Snow can be used in `no_std` environments if `alloc` is provided.
+
+By default Snow uses the standard library, default cyprot resolver and a selected collection 
+of crypto primitives. To use Snow in `no_std` environments or make other kinds of customized 
+setups, use Snow with `default-features = false`. This way you will individually select 
+the components you wish to use. `default-resolver` is the only built-in resolver that 
+currently supports `no_std`.
+
+To use a custom setup with `default-resolver`, enable your desired selection of cryptographic primitives:
+
+| Primitive    | Feature flag           |
+| :----------- | ---------------------: |
+| **DH**                                |
+| 25519        | `use-curve25519-dalek` |
+| **Cipher**                            |
+| AESGCM       | `use-aes-gcm`          |
+| ChaChaPoly   | `use-chacha20poly1305` |
+| XChaChaPoly* | `use-xchacha20poly1305`|
+| **Hash**                              |
+| SHA256       | `use-sha2`             |
+| SHA512       | `use-sha2`             |
+| BLAKE2s      | `use-blake2`           |
+| BLAKE2b      | `use-blake2`           |
+
+\* *XChaChaPoly*, an extended nonce variant of *ChaChaPoly*, is not in the official specification of Noise!
+
+### Example configurations
+
+**25519 + AES-GCM + SHA** with standard library features.
+```toml
+default-features = false
+features = [
+    "use-curve25519-dalek",
+    "use-aes-gcm",
+    "use-sha2",
+    "std",
+]
+```
+
+**25519 + ChaChaPoly + BLAKE2** without standard library.
+```toml
+default-features = false
+features = [
+    "use-curve25519-dalek",
+    "use-chacha20poly1305",
+    "use-blake2",
+]
+```
+
+### `getrandom` support
+
+Most crypto implementations supported by `default-resolver` will require 
+[`getrandom`](getrandom).
+
+If your target platform is not directly supported 
+you might have to provide a custom implementation in your crate root. 
+Check out their [documentation](getrandom-custom) for details.
+
+[getrandom]: https://crates.io/crates/getrandom
+[getrandom-custom]: https://docs.rs/getrandom/0.2.15/getrandom/macro.register_custom_getrandom.html
+
 ## License
 
 Licensed under either of:

ci-tests.sh

@@ -7,12 +7,15 @@ COMMON_FEATURES="xchachapoly vector-tests"
 set -x
 cargo check --benches
 cargo test $TARGET --no-default-features
-cargo test $TARGET --features "$COMMON_FEATURES"
+# Custom set of crypto without std
+cargo test $TARGET --no-default-features --features "default-resolver use-curve25519-dalek use-blake2 use-chacha20poly1305"
+# Custom set of crypto with std
+cargo test $TARGET --no-default-features --features "default-resolver use-curve25519-dalek use-sha2 use-chacha20poly1305"
 cargo test $TARGET --features "ring-resolver $COMMON_FEATURES"
 cargo test $TARGET --features "ring-accelerated $COMMON_FEATURES"
 if ! rustc -vV | grep 'host: .*windows' &> /dev/null; then
-    cargo test $TARGET --features "hfs pqclean_kyber1024 $COMMON_FEATURES"
-    cargo test $TARGET --features "ring-resolver hfs pqclean_kyber1024 $COMMON_FEATURES"
+    cargo test $TARGET --features "hfs use-pqcrypto-kyber1024 $COMMON_FEATURES"
+    cargo test $TARGET --features "ring-resolver hfs use-pqcrypto-kyber1024 $COMMON_FEATURES"
 fi
 cargo test $TARGET --features "libsodium-resolver $COMMON_FEATURES"
 cargo test $TARGET --features "libsodium-accelerated $COMMON_FEATURES"

src/builder.rs

@@ -1,4 +1,7 @@
-use std::fmt::Debug;
+use core::fmt::Debug;
+
+#[cfg(not(feature = "std"))]
+use alloc::{boxed::Box, vec, vec::Vec};
 
 #[cfg(feature = "hfs")]
 use crate::params::HandshakeModifier;
@@ -45,7 +48,7 @@ impl PartialEq for Keypair {
 /// # use snow::Builder;
 /// # let my_long_term_key = [0u8; 32];
 /// # let their_pub_key = [0u8; 32];
-/// # #[cfg(any(feature = "default-resolver", feature = "ring-accelerated"))]
+/// # #[cfg(any(feature = "default-resolver-crypto", feature = "ring-accelerated"))]
 /// let noise = Builder::new("Noise_XX_25519_ChaChaPoly_BLAKE2s".parse()?)
 ///     .local_private_key(&my_long_term_key)?
 ///     .remote_public_key(&their_pub_key)?
@@ -65,7 +68,7 @@ pub struct Builder<'builder> {
 }
 
 impl<'builder> Debug for Builder<'builder> {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
         f.debug_struct("Builder").field("params", &self.params.name).finish_non_exhaustive()
     }
 }
@@ -317,8 +320,12 @@ impl<'builder> Builder<'builder> {
     }
 }
 
+
 #[cfg(test)]
-#[cfg(any(feature = "default-resolver", feature = "ring-accelerated"))]
+#[cfg(all(
+    feature = "std",
+    any(feature = "default-resolver-crypto", feature = "ring-accelerated")
+))]
 mod tests {
     use super::*;
     type TestResult = Result<(), Box<dyn std::error::Error>>;

src/cipherstate.rs

@@ -1,3 +1,6 @@
+#[cfg(not(feature = "std"))]
+use alloc::boxed::Box;
+
 use crate::{
     constants::{CIPHERKEYLEN, TAGLEN},
     error::{Error, InitStage, StateProblem},

src/error.rs

@@ -1,6 +1,6 @@
 //! All error types used by Snow operations.
 
-use std::fmt;
+use core::fmt;
 
 /// `snow` provides decently detailed errors, exposed as the [`Error`] enum,
 /// to allow developers to react to errors in a more actionable way.
@@ -181,4 +181,5 @@ impl fmt::Display for Error {
     }
 }
 
+#[cfg(feature = "std")]
 impl std::error::Error for Error {}

src/handshakestate.rs

@@ -15,7 +15,9 @@ use crate::{
     types::{Dh, Hash, Random},
     utils::Toggle,
 };
-use std::{
+#[cfg(not(feature = "std"))]
+use alloc::boxed::Box;
+use core::{
     convert::{TryFrom, TryInto},
     fmt,
 };

src/lib.rs

@@ -13,7 +13,7 @@
 //! ```
 //! # use snow::Error;
 //! #
-//! # #[cfg(any(feature = "default-resolver", feature = "ring-accelerated"))]
+//! # #[cfg(any(feature = "default-resolver-crypto", feature = "ring-accelerated"))]
 //! # fn try_main() -> Result<(), Error> {
 //! static PATTERN: &'static str = "Noise_NN_25519_ChaChaPoly_BLAKE2s";
 //!
@@ -43,7 +43,7 @@
 //! #     Ok(())
 //! # }
 //! #
-//! # #[cfg(not(any(feature = "default-resolver", feature = "ring-accelerated")))]
+//! # #[cfg(not(any(feature = "default-resolver-crypto", feature = "ring-accelerated")))]
 //! # fn try_main() -> Result<(), ()> { Ok(()) }
 //! #
 //! # fn main() {
@@ -54,6 +54,26 @@
 //! See `examples/simple.rs` for a more complete TCP client/server example with static keys.
 
 #![warn(missing_docs)]
+#![cfg_attr(not(feature = "std"), no_std)]
+
+#[cfg(not(feature = "std"))]
+extern crate alloc;
+
+// Make sure the user is running a supported configuration.
+#[cfg(feature = "default-resolver")]
+#[cfg(any(
+    not(any(feature = "use-curve25519-dalek")),
+    not(any(
+        feature = "use-aes-gcm",
+        feature = "use-chacha20poly1305",
+        feature = "use-xchacha20poly1305"
+    )),
+    not(any(feature = "use-sha2", feature = "use-blake2"))
+))]
+compile_error!(
+    "Valid selection of crypto primitived must be enabled when using feature 'default-resolver'.
+    Enable at least one DH feature, one Cipher feature and one Hash feature. Check README.md for details."
+);
 
 macro_rules! copy_slices {
     ($inslice:expr, $outslice:expr) => {

src/params/mod.rs

@@ -4,8 +4,11 @@
 //! All structures related to Noise parameter definitions (cryptographic primitive choices, protocol
 //! patterns/names)
 
+#[cfg(not(feature = "std"))]
+use alloc::{borrow::ToOwned, string::String};
+
 use crate::error::{Error, PatternProblem};
-use std::str::FromStr;
+use core::str::FromStr;
 mod patterns;
 
 pub use self::patterns::{
@@ -61,7 +64,7 @@ impl FromStr for DHChoice {
 pub enum CipherChoice {
     /// The ChaCha20Poly1305 AEAD.
     ChaChaPoly,
-    #[cfg(feature = "xchachapoly")]
+    #[cfg(feature = "use-xchacha20poly1305")]
     /// The XChaCha20Poly1305 AEAD, an extended nonce variant of ChaCha20Poly1305.
     /// This variant is hidden behind a feature flag to highlight that it is not in the
     /// official specification of the Noise Protocol.
@@ -77,7 +80,7 @@ impl FromStr for CipherChoice {
         use self::CipherChoice::*;
         match s {
             "ChaChaPoly" => Ok(ChaChaPoly),
-            #[cfg(feature = "xchachapoly")]
+            #[cfg(feature = "use-xchacha20poly1305")]
             "XChaChaPoly" => Ok(XChaChaPoly),
             "AESGCM" => Ok(AESGCM),
             _ => Err(PatternProblem::UnsupportedCipherType.into()),
@@ -257,7 +260,7 @@ impl FromStr for NoiseParams {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use std::convert::TryFrom;
+    use core::convert::TryFrom;
 
     #[test]
     fn test_simple_handshake() {

src/params/patterns.rs

@@ -1,7 +1,10 @@
 #![allow(clippy::enum_glob_use)]
 
+#[cfg(not(feature = "std"))]
+use alloc::{vec, vec::Vec};
+
 use crate::error::{Error, PatternProblem};
-use std::{convert::TryFrom, str::FromStr};
+use core::{convert::TryFrom, str::FromStr};
 
 /// A small helper macro that behaves similar to the `vec![]` standard macro,
 /// except it allocates a bit extra to avoid resizing.