Add no_std support to transcript, dalek-ff-group, ed448, ciphersuite, multiexp, schnorr, and monero-generators

transcript, dalek-ff-group, ed449, and ciphersuite are all usable with no_std
alone. The rest additionally require alloc.

Part of #279.

crypto/schnorr/Cargo.toml

@@ -13,17 +13,27 @@ all-features = true
 rustdoc-args = ["--cfg", "docsrs"]
 
 [dependencies]
-rand_core = "0.6"
+std-shims = { path = "../../common/std-shims", version = "0.1", default-features = false }
+
+rand_core = { version = "0.6", default-features = false }
 
 zeroize = { version = "^1.5", features = ["zeroize_derive"] }
 
-transcript = { package = "flexible-transcript", path = "../transcript", version = "0.3" }
+transcript = { package = "flexible-transcript", path = "../transcript", version = "0.3", default-features = false }
 
-ciphersuite = { path = "../ciphersuite", version = "0.3" }
-multiexp = { path = "../multiexp", version = "0.3", features = ["batch"] }
+ciphersuite = { path = "../ciphersuite", version = "0.3", default-features = false, features = ["alloc"] }
+multiexp = { path = "../multiexp", version = "0.3", default-features = false, features = ["batch"] }
 
 [dev-dependencies]
 hex = "0.4"
+
+rand_core = { version = "0.6", features = ["std"] }
+
 sha2 = "0.10"
+
 dalek-ff-group = { path =  "../dalek-ff-group", version = "0.3" }
 ciphersuite = { path = "../ciphersuite", version = "0.3", features = ["ed25519"] }
+
+[features]
+std = ["std-shims/std", "ciphersuite/std"]
+default = ["std"]

crypto/schnorr/README.md

@@ -14,3 +14,6 @@ This library was
 culminating in commit
 [669d2dbffc1dafb82a09d9419ea182667115df06](https://github.com/serai-dex/serai/tree/669d2dbffc1dafb82a09d9419ea182667115df06).
 Any subsequent changes have not undergone auditing.
+
+This library is usable under no_std, via alloc, when the default features are
+disabled.

crypto/schnorr/src/aggregate.rs

@@ -1,4 +1,7 @@
-use std::io::{self, Read, Write};
+use std_shims::{
+  vec::Vec,
+  io::{self, Read, Write},
+};
 
 use zeroize::Zeroize;
 

crypto/schnorr/src/lib.rs

@@ -1,8 +1,15 @@
 #![cfg_attr(docsrs, feature(doc_auto_cfg))]
 #![doc = include_str!("../README.md")]
+#![cfg_attr(not(feature = "std"), no_std)]
 
 use core::ops::Deref;
-use std::io::{self, Read, Write};
+#[cfg(not(feature = "std"))]
+#[macro_use]
+extern crate alloc;
+use std_shims::{
+  vec::Vec,
+  io::{self, Read, Write},
+};
 
 use rand_core::{RngCore, CryptoRng};