Pull in fork of sha2 that exposes compress256 round function

Cargo.lock

@@ -197,7 +197,7 @@ version = "0.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b170cd256a3f9fa6b9edae3e44a7dfdfc77e8124dbc3e2612d75f9c3e2396dae"
 dependencies = [
- "sha2",
+ "sha2 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -390,7 +390,7 @@ dependencies = [
  "curve25519-dalek",
  "rand_core 0.5.1",
  "serde",
- "sha2",
+ "sha2 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "thiserror",
 ]
 
@@ -1511,6 +1511,17 @@ dependencies = [
  "yaml-rust",
 ]
 
+[[package]]
+name = "sha2"
+version = "0.8.1"
+source = "git+https://github.com/ZcashFoundation/hashes?branch=expose-utils#a968a8db2bffae75fbb31596897be9088ddbb821"
+dependencies = [
+ "block-buffer",
+ "digest",
+ "fake-simd",
+ "opaque-debug",
+]
+
 [[package]]
 name = "sha2"
 version = "0.8.1"
@@ -2070,7 +2081,7 @@ dependencies = [
  "ripemd160",
  "secp256k1",
  "serde",
- "sha2",
+ "sha2 0.8.1 (git+https://github.com/ZcashFoundation/hashes?branch=expose-utils)",
  "thiserror",
  "x25519-dalek",
 ]

zebra-chain/Cargo.toml

@@ -17,12 +17,13 @@ lazy_static = "1.4.0"
 ripemd160 = "0.8.0"
 secp256k1 = { version = "0.17.2", features = ["serde"] }
 serde = { version = "1", features = ["serde_derive"] }
-sha2 = "0.8"
+# sha2 = "0.8"
 thiserror = "1"
 x25519-dalek = "0.6"
 # ZF deps
-redjubjub = "0.1"
 ed25519-zebra = "0.2"
+redjubjub = "0.1"
+sha2 = {git="https://github.com/ZcashFoundation/hashes", branch = "expose-utils", features=["utils"]}
 
 [dev-dependencies]
 proptest = "0.9"

zebra-chain/src/keys/sprout.rs

@@ -16,14 +16,25 @@ use proptest::{array, collection::vec, prelude::*};
 #[cfg(test)]
 use proptest_derive::Arbitrary;
 
+use sha2::sha256_utils::compress256;
+
 use crate::serialization::{SerializationError, ZcashDeserialize, ZcashSerialize};
 
+/// Our root secret key of the Sprout key derivation tree.
+///
 /// All other Sprout key types derive from the SpendingKey value.
-pub struct SpendingKey;
+/// Actually 252 bits.
+pub struct SpendingKey(pub [u8; 32]);
 
 /// Derived from a _SpendingKey_.
 pub type ReceivingKey = x25519_dalek::StaticSecret;
 
+impl From<SpendingKey> for ReceivingKey {
+    fn from(spending_key: SpendingKey) -> ReceivingKey {
+        ReceivingKey::from(spending_key.0)
+    }
+}
+
 /// Derived from a _SpendingKey_.
 #[derive(Copy, Clone, Eq, PartialEq)]
 pub struct PayingKey(pub [u8; 32]);