Expose std_shims::io on core

The `io::Write` trait is somewhat worthless, being implemented for nothing, yet
`Read` remains fully functional. This also allows using its polyfills _without_
requiring `alloc`.

Opportunity taken to make `schnorr-signatures` not require `alloc`.

This will require a version bump before being published due to newly requiring
the `alloc` feature be specified to maintain pre-existing behavior.

Enables resolving https://github.com/monero-oxide/monero-oxide/issues/48.

crypto/ciphersuite/Cargo.toml

@@ -17,7 +17,7 @@ rustdoc-args = ["--cfg", "docsrs"]
 workspace = true
 
 [dependencies]
-std-shims = { path = "../../common/std-shims", version = "0.1.4", default-features = false, optional = true }
+std-shims = { path = "../../common/std-shims", version = "0.1.4", default-features = false }
 
 zeroize = { version = "^1.5", default-features = false, features = ["derive"] }
 subtle = { version = "^2.4", default-features = false }
@@ -33,7 +33,7 @@ hex = { version = "0.4", default-features = false, features = ["std"] }
 ff-group-tests = { version = "0.13", path = "../ff-group-tests" }
 
 [features]
-alloc = ["std-shims", "zeroize/alloc", "digest/alloc", "ff/alloc"]
+alloc = ["zeroize/alloc", "digest/alloc", "ff/alloc"]
 std = [
   "alloc",
 

crypto/ciphersuite/src/lib.rs

@@ -3,10 +3,8 @@
 #![cfg_attr(not(feature = "std"), no_std)]
 
 use core::fmt::Debug;
-#[cfg(feature = "alloc")]
 #[allow(unused_imports)]
 use std_shims::prelude::*;
-#[cfg(feature = "alloc")]
 use std_shims::io::{self, Read};
 
 use subtle::{CtOption, ConstantTimeEq, ConditionallySelectable};
@@ -112,7 +110,6 @@ pub trait GroupCanonicalEncoding: WrappedGroup {
 }
 
 /// `std::io` extensions for `GroupCanonicalEncoding.`
-#[cfg(feature = "alloc")]
 #[allow(non_snake_case)]
 pub trait GroupIo: GroupCanonicalEncoding {
   /// Read a canonical field element from something implementing `std::io::Read`.
@@ -129,8 +126,6 @@ pub trait GroupIo: GroupCanonicalEncoding {
   }
 
   /// Read a canonical point from something implementing `std::io::Read`.
-  #[cfg(feature = "alloc")]
-  #[allow(non_snake_case)]
   fn read_G<R: Read>(reader: &mut R) -> io::Result<Self::G> {
     let mut bytes = <Self::G as GroupEncoding>::Repr::default();
     reader.read_exact(bytes.as_mut())?;

crypto/embedwards25519/Cargo.toml

@@ -16,7 +16,7 @@ rustdoc-args = ["--cfg", "docsrs"]
 [dependencies]
 hex-literal = { version = "1", default-features = false }
 
-std-shims = { version = "0.1", path = "../../common/std-shims", default-features = false, optional = true }
+std-shims = { version = "0.1", path = "../../common/std-shims", default-features = false }
 
 zeroize = { version = "^1.5", default-features = false, features = ["zeroize_derive"] }
 
@@ -39,6 +39,6 @@ rand_core = { version = "0.6", features = ["std"] }
 ff-group-tests = { path = "../ff-group-tests" }
 
 [features]
-alloc = ["std-shims", "zeroize/alloc", "prime-field/alloc", "short-weierstrass/alloc", "curve25519-dalek/alloc", "blake2/alloc", "ciphersuite/alloc", "generalized-bulletproofs-ec-gadgets"]
+alloc = ["zeroize/alloc", "prime-field/alloc", "short-weierstrass/alloc", "curve25519-dalek/alloc", "blake2/alloc", "ciphersuite/alloc", "generalized-bulletproofs-ec-gadgets"]
 std = ["alloc", "std-shims/std", "zeroize/std", "prime-field/std", "short-weierstrass/std", "ciphersuite/std", "generalized-bulletproofs-ec-gadgets/std"]
 default = ["std"]

crypto/embedwards25519/src/lib.rs

@@ -2,7 +2,6 @@
 #![doc = include_str!("../README.md")]
 #![cfg_attr(not(feature = "std"), no_std)]
 
-#[cfg(feature = "alloc")]
 #[allow(unused_imports)]
 use std_shims::prelude::*;
 

crypto/schnorr/Cargo.toml

@@ -26,8 +26,8 @@ digest = { version = "0.11.0-rc.1", default-features = false, features = ["block
 
 transcript = { package = "flexible-transcript", path = "../transcript", version = "^0.3.2", default-features = false, optional = true }
 
-ciphersuite = { path = "../ciphersuite", version = "^0.4.1", default-features = false, features = ["alloc"] }
-multiexp = { path = "../multiexp", version = "0.4", default-features = false, features = ["batch"] }
+ciphersuite = { path = "../ciphersuite", version = "^0.4.1", default-features = false }
+multiexp = { path = "../multiexp", version = "0.4", default-features = false, features = ["batch"], optional = true }
 
 [dev-dependencies]
 hex = "0.4"
@@ -40,6 +40,7 @@ dalek-ff-group = { path =  "../dalek-ff-group" }
 ciphersuite = { path = "../ciphersuite" }
 
 [features]
-aggregate = ["transcript"]
-std = ["std-shims/std", "rand_core/std", "zeroize/std", "transcript?/std", "ciphersuite/std", "multiexp/std"]
+alloc = ["zeroize/alloc", "digest/alloc", "ciphersuite/alloc", "multiexp"]
+aggregate = ["alloc", "transcript"]
+std = ["alloc", "std-shims/std", "rand_core/std", "zeroize/std", "transcript?/std", "ciphersuite/std", "multiexp/std"]
 default = ["std"]

crypto/schnorr/src/lib.rs

@@ -3,14 +3,15 @@
 #![cfg_attr(not(feature = "std"), no_std)]
 
 use core::ops::Deref;
-#[cfg(not(feature = "std"))]
-#[macro_use]
+#[cfg(all(feature = "alloc", not(feature = "std")))]
 extern crate alloc;
-use std_shims::{
-  vec::Vec,
-  io::{self, Read, Write},
-};
+#[cfg(all(feature = "alloc", not(feature = "std")))]
+use alloc::vec::Vec;
+#[allow(unused_imports)]
+use std_shims::prelude::*;
+use std_shims::io::{self, Read, Write};
 
+#[cfg(feature = "alloc")]
 use rand_core::{RngCore, CryptoRng};
 
 use zeroize::{Zeroize, Zeroizing};
@@ -22,6 +23,7 @@ use ciphersuite::{
   },
   GroupIo,
 };
+#[cfg(feature = "alloc")]
 use multiexp::{multiexp_vartime, BatchVerifier};
 
 /// Half-aggregation from <https://eprint.iacr.org/2021/350>.
@@ -59,6 +61,7 @@ impl<C: GroupIo> SchnorrSignature<C> {
   }
 
   /// Serialize a SchnorrSignature, returning a `Vec<u8>`.
+  #[cfg(feature = "alloc")]
   pub fn serialize(&self) -> Vec<u8> {
     let mut buf = vec![];
     self.write(&mut buf).unwrap();
@@ -106,7 +109,12 @@ impl<C: GroupIo> SchnorrSignature<C> {
   /// different keys/messages.
   #[must_use]
   pub fn verify(&self, public_key: C::G, challenge: C::F) -> bool {
-    multiexp_vartime(&self.batch_statements(public_key, challenge)).is_identity().into()
+    let statements = self.batch_statements(public_key, challenge);
+    #[cfg(feature = "alloc")]
+    let res = multiexp_vartime(&statements);
+    #[cfg(not(feature = "alloc"))]
+    let res = statements.into_iter().map(|(scalar, point)| point * scalar).sum::<C::G>();
+    res.is_identity().into()
   }
 
   /// Queue a signature for batch verification.
@@ -114,6 +122,7 @@ impl<C: GroupIo> SchnorrSignature<C> {
   /// This challenge must be properly crafted, which means being binding to the public key, nonce,
   /// and any message. Failure to do so will let a malicious adversary to forge signatures for
   /// different keys/messages.
+  #[cfg(feature = "alloc")]
   pub fn batch_verify<R: RngCore + CryptoRng, I: Copy + Zeroize>(
     &self,
     rng: &mut R,

crypto/secq256k1/Cargo.toml

@@ -16,7 +16,7 @@ rustdoc-args = ["--cfg", "docsrs"]
 [dependencies]
 hex-literal = { version = "1", default-features = false }
 
-std-shims = { version = "0.1", path = "../../common/std-shims", default-features = false, optional = true }
+std-shims = { version = "0.1", path = "../../common/std-shims", default-features = false }
 
 sha2 = { version = "0.11.0-rc.0", default-features = false }
 k256 = { version = "0.13", default-features = false, features = ["arithmetic", "expose-field"] }
@@ -34,6 +34,6 @@ rand_core = { version = "0.6", features = ["std"] }
 ff-group-tests = { path = "../ff-group-tests" }
 
 [features]
-alloc = ["std-shims", "k256/alloc", "prime-field/alloc", "short-weierstrass/alloc", "sha2/alloc", "ciphersuite/alloc", "generalized-bulletproofs-ec-gadgets"]
+alloc = ["k256/alloc", "prime-field/alloc", "short-weierstrass/alloc", "sha2/alloc", "ciphersuite/alloc", "generalized-bulletproofs-ec-gadgets"]
 std = ["alloc", "std-shims/std", "k256/std", "prime-field/std", "ciphersuite/std", "generalized-bulletproofs-ec-gadgets/std"]
 default = ["std"]

crypto/secq256k1/src/lib.rs

@@ -2,7 +2,6 @@
 #![doc = include_str!("../README.md")]
 #![cfg_attr(not(feature = "std"), no_std)]
 
-#[cfg(feature = "alloc")]
 #[allow(unused_imports)]
 use std_shims::prelude::*;