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.

coins/monero/generators/Cargo.toml

@@ -12,13 +12,20 @@ all-features = true
 rustdoc-args = ["--cfg", "docsrs"]
 
 [dependencies]
+std-shims = { path = "../../../common/std-shims", version = "0.1", default-features = false }
+
 lazy_static = "1"
 
-subtle = "^2.4"
+subtle = { version = "^2.4", default-features = false }
 
-sha3 = "0.10"
+sha3 = { version = "0.10", default-features = false }
 
-curve25519-dalek = { version = "3", features = ["std"] }
+curve25519-dalek = { version = "3", default-features = false }
 
-group = "0.13"
+group = { version = "0.13", default-features = false }
 dalek-ff-group = { path = "../../../crypto/dalek-ff-group", version = "0.3" }
+
+[features]
+alloc = ["lazy_static/spin_no_std"]
+std = ["std-shims/std"]
+default = ["std"]

coins/monero/generators/README.md

@@ -3,3 +3,5 @@
 Generators used by Monero in both its Pedersen commitments and Bulletproofs(+).
 An implementation of Monero's `ge_fromfe_frombytes_vartime`, simply called
 `hash_to_point` here, is included, as needed to generate generators.
+
+This library is usable under no_std when the `alloc` feature is enabled.

coins/monero/generators/src/lib.rs

@@ -2,16 +2,15 @@
 //! An implementation of Monero's `ge_fromfe_frombytes_vartime`, simply called
 //! `hash_to_point` here, is included, as needed to generate generators.
 
+#![cfg_attr(not(feature = "std"), no_std)]
+
 use lazy_static::lazy_static;
 
 use sha3::{Digest, Keccak256};
 
-use curve25519_dalek::{
-  constants::ED25519_BASEPOINT_POINT,
-  edwards::{EdwardsPoint as DalekPoint, CompressedEdwardsY},
-};
+use curve25519_dalek::edwards::{EdwardsPoint as DalekPoint, CompressedEdwardsY};
 
-use group::Group;
+use group::{Group, GroupEncoding};
 use dalek_ff_group::EdwardsPoint;
 
 mod varint;
@@ -27,7 +26,7 @@ fn hash(data: &[u8]) -> [u8; 32] {
 lazy_static! {
   /// Monero alternate generator `H`, used for amounts in Pedersen commitments.
   pub static ref H: DalekPoint =
-    CompressedEdwardsY(hash(&ED25519_BASEPOINT_POINT.compress().to_bytes()))
+    CompressedEdwardsY(hash(&EdwardsPoint::generator().to_bytes()))
       .decompress()
       .unwrap()
       .mul_by_cofactor();

coins/monero/generators/src/varint.rs

@@ -1,4 +1,4 @@
-use std::io::{self, Write};
+use std_shims::io::{self, Write};
 
 const VARINT_CONTINUATION_MASK: u8 = 0b1000_0000;
 pub(crate) fn write_varint<W: Write>(varint: &u64, w: &mut W) -> io::Result<()> {