From 5a44c36b1f704dc9701ebf37d5dd49c097b2eb9d Mon Sep 17 00:00:00 2001
From: Greg Fitzgerald <garious@gmail.com>
Date: Tue, 6 Mar 2018 17:20:37 -0700
Subject: [PATCH 1/3] Move hash into its own module

---
 src/accountant.rs      |  3 ++-
 src/accountant_skel.rs |  3 ++-
 src/accountant_stub.rs |  3 ++-
 src/bin/demo.rs        |  3 ++-
 src/genesis.rs         |  3 ++-
 src/hash.rs            | 19 +++++++++++++++++++
 src/historian.rs       |  3 ++-
 src/lib.rs             |  1 +
 src/log.rs             | 20 +-------------------
 src/logger.rs          |  3 ++-
 src/transaction.rs     |  4 ++--
 11 files changed, 37 insertions(+), 28 deletions(-)
 create mode 100644 src/hash.rs

diff --git a/src/accountant.rs b/src/accountant.rs
index 3af3949652..61838382cf 100644
--- a/src/accountant.rs
+++ b/src/accountant.rs
@@ -2,7 +2,8 @@
 //! event log to record transactions. Its users can deposit funds and
 //! transfer funds to other users.
 
-use log::{Entry, Sha256Hash};
+use hash::Sha256Hash;
+use log::Entry;
 use event::Event;
 use transaction::Transaction;
 use signature::{PublicKey, Signature};
diff --git a/src/accountant_skel.rs b/src/accountant_skel.rs
index 4c6c12a981..9296b6a171 100644
--- a/src/accountant_skel.rs
+++ b/src/accountant_skel.rs
@@ -2,7 +2,8 @@ use std::io;
 use accountant::Accountant;
 use transaction::Transaction;
 use signature::PublicKey;
-use log::{Entry, Sha256Hash};
+use hash::Sha256Hash;
+use log::Entry;
 use std::net::UdpSocket;
 use bincode::{deserialize, serialize};
 
diff --git a/src/accountant_stub.rs b/src/accountant_stub.rs
index ea713a9b5f..1bded971ec 100644
--- a/src/accountant_stub.rs
+++ b/src/accountant_stub.rs
@@ -7,7 +7,8 @@ use std::io;
 use bincode::{deserialize, serialize};
 use transaction::Transaction;
 use signature::{PublicKey, Signature};
-use log::{Entry, Sha256Hash};
+use hash::Sha256Hash;
+use log::Entry;
 use ring::signature::Ed25519KeyPair;
 use accountant_skel::{Request, Response};
 
diff --git a/src/bin/demo.rs b/src/bin/demo.rs
index bdbad0ba23..76c27dc306 100644
--- a/src/bin/demo.rs
+++ b/src/bin/demo.rs
@@ -1,7 +1,8 @@
 extern crate silk;
 
 use silk::historian::Historian;
-use silk::log::{verify_slice, Entry, Sha256Hash};
+use silk::hash::Sha256Hash;
+use silk::log::{verify_slice, Entry};
 use silk::signature::{generate_keypair, get_pubkey};
 use silk::transaction::Transaction;
 use silk::event::Event;
diff --git a/src/genesis.rs b/src/genesis.rs
index 01bcd1416d..6ef4151ad2 100644
--- a/src/genesis.rs
+++ b/src/genesis.rs
@@ -3,7 +3,8 @@
 use event::Event;
 use transaction::Transaction;
 use signature::{generate_keypair, get_pubkey, PublicKey};
-use log::{create_entries, hash, Entry, Sha256Hash};
+use log::{create_entries, Entry};
+use hash::{hash, Sha256Hash};
 use ring::rand::SystemRandom;
 use ring::signature::Ed25519KeyPair;
 use untrusted::Input;
diff --git a/src/hash.rs b/src/hash.rs
new file mode 100644
index 0000000000..5efb933f5f
--- /dev/null
+++ b/src/hash.rs
@@ -0,0 +1,19 @@
+use generic_array::GenericArray;
+use generic_array::typenum::U32;
+use sha2::{Digest, Sha256};
+
+pub type Sha256Hash = GenericArray<u8, U32>;
+
+/// Return a Sha256 hash for the given data.
+pub fn hash(val: &[u8]) -> Sha256Hash {
+    let mut hasher = Sha256::default();
+    hasher.input(val);
+    hasher.result()
+}
+
+/// Return the hash of the given hash extended with the given value.
+pub fn extend_and_hash(id: &Sha256Hash, val: &[u8]) -> Sha256Hash {
+    let mut hash_data = id.to_vec();
+    hash_data.extend_from_slice(val);
+    hash(&hash_data)
+}
diff --git a/src/historian.rs b/src/historian.rs
index 03605a247c..f0683c8f7b 100644
--- a/src/historian.rs
+++ b/src/historian.rs
@@ -5,7 +5,8 @@ use std::thread::{spawn, JoinHandle};
 use std::collections::HashSet;
 use std::sync::mpsc::{sync_channel, Receiver, SyncSender};
 use std::time::Instant;
-use log::{hash, Entry, Sha256Hash};
+use hash::{hash, Sha256Hash};
+use log::Entry;
 use logger::{ExitReason, Logger};
 use signature::Signature;
 use event::Event;
diff --git a/src/lib.rs b/src/lib.rs
index 91cbf8b703..4551c6833b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,4 +1,5 @@
 #![cfg_attr(feature = "unstable", feature(test))]
+pub mod hash;
 pub mod log;
 pub mod logger;
 pub mod event;
diff --git a/src/log.rs b/src/log.rs
index 1da66d778f..6a13f3abef 100644
--- a/src/log.rs
+++ b/src/log.rs
@@ -13,15 +13,11 @@
 /// fastest processor. Duration should therefore be estimated by assuming that the hash
 /// was generated by the fastest processor at the time the entry was logged.
 
-use generic_array::GenericArray;
-use generic_array::typenum::U32;
+use hash::{extend_and_hash, hash, Sha256Hash};
 use serde::Serialize;
 use event::Event;
-use sha2::{Digest, Sha256};
 use rayon::prelude::*;
 
-pub type Sha256Hash = GenericArray<u8, U32>;
-
 #[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
 pub struct Entry<T> {
     pub num_hashes: u64,
@@ -50,20 +46,6 @@ impl<T: Serialize> Entry<T> {
     }
 }
 
-/// Return a Sha256 hash for the given data.
-pub fn hash(val: &[u8]) -> Sha256Hash {
-    let mut hasher = Sha256::default();
-    hasher.input(val);
-    hasher.result()
-}
-
-/// Return the hash of the given hash extended with the given value.
-pub fn extend_and_hash(id: &Sha256Hash, val: &[u8]) -> Sha256Hash {
-    let mut hash_data = id.to_vec();
-    hash_data.extend_from_slice(val);
-    hash(&hash_data)
-}
-
 /// Creates the hash 'num_hashes' after start_hash. If the event contains
 /// signature, the final hash will be a hash of both the previous ID and
 /// the signature.
diff --git a/src/logger.rs b/src/logger.rs
index 8fcf101f6d..8f47bc97c5 100644
--- a/src/logger.rs
+++ b/src/logger.rs
@@ -7,7 +7,8 @@
 
 use std::sync::mpsc::{Receiver, SyncSender, TryRecvError};
 use std::time::{Duration, Instant};
-use log::{create_entry_mut, Entry, Sha256Hash};
+use hash::Sha256Hash;
+use log::{create_entry_mut, Entry};
 use event::Event;
 use serde::Serialize;
 use std::fmt::Debug;
diff --git a/src/transaction.rs b/src/transaction.rs
index f0be7c1d89..1193358668 100644
--- a/src/transaction.rs
+++ b/src/transaction.rs
@@ -4,7 +4,7 @@ use signature::{get_pubkey, verify_signature, PublicKey, Signature};
 use ring::signature::Ed25519KeyPair;
 use serde::Serialize;
 use bincode::serialize;
-use log::Sha256Hash;
+use hash::Sha256Hash;
 
 #[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
 pub struct Transaction<T> {
@@ -51,8 +51,8 @@ impl<T: Serialize> Transaction<T> {
 mod tests {
     use super::*;
     use bincode::{deserialize, serialize};
-    use log::*;
     use signature::*;
+    use hash::hash;
 
     #[test]
     fn test_claim() {

From 1436bb1ff2f12228ecc69fc1d10197daf3638ce6 Mon Sep 17 00:00:00 2001
From: Greg Fitzgerald <garious@gmail.com>
Date: Tue, 6 Mar 2018 17:31:17 -0700
Subject: [PATCH 2/3] Move entry into its own module

Hmm, Logger doesn't depend on log.
---
 src/accountant.rs      |   2 +-
 src/accountant_skel.rs |   2 +-
 src/accountant_stub.rs |   2 +-
 src/bin/demo.rs        |   3 +-
 src/entry.rs           | 110 +++++++++++++++++++++++++++++++++++++++++
 src/genesis.rs         |   3 +-
 src/historian.rs       |   2 +-
 src/lib.rs             |  11 +++--
 src/log.rs             | 106 ++-------------------------------------
 src/logger.rs          |   2 +-
 10 files changed, 128 insertions(+), 115 deletions(-)
 create mode 100644 src/entry.rs

diff --git a/src/accountant.rs b/src/accountant.rs
index 61838382cf..0bc97f5a68 100644
--- a/src/accountant.rs
+++ b/src/accountant.rs
@@ -3,7 +3,7 @@
 //! transfer funds to other users.
 
 use hash::Sha256Hash;
-use log::Entry;
+use entry::Entry;
 use event::Event;
 use transaction::Transaction;
 use signature::{PublicKey, Signature};
diff --git a/src/accountant_skel.rs b/src/accountant_skel.rs
index 9296b6a171..9cd25dad08 100644
--- a/src/accountant_skel.rs
+++ b/src/accountant_skel.rs
@@ -3,7 +3,7 @@ use accountant::Accountant;
 use transaction::Transaction;
 use signature::PublicKey;
 use hash::Sha256Hash;
-use log::Entry;
+use entry::Entry;
 use std::net::UdpSocket;
 use bincode::{deserialize, serialize};
 
diff --git a/src/accountant_stub.rs b/src/accountant_stub.rs
index 1bded971ec..61529642ae 100644
--- a/src/accountant_stub.rs
+++ b/src/accountant_stub.rs
@@ -8,7 +8,7 @@ use bincode::{deserialize, serialize};
 use transaction::Transaction;
 use signature::{PublicKey, Signature};
 use hash::Sha256Hash;
-use log::Entry;
+use entry::Entry;
 use ring::signature::Ed25519KeyPair;
 use accountant_skel::{Request, Response};
 
diff --git a/src/bin/demo.rs b/src/bin/demo.rs
index 76c27dc306..75614d56a1 100644
--- a/src/bin/demo.rs
+++ b/src/bin/demo.rs
@@ -2,7 +2,8 @@ extern crate silk;
 
 use silk::historian::Historian;
 use silk::hash::Sha256Hash;
-use silk::log::{verify_slice, Entry};
+use silk::entry::Entry;
+use silk::log::verify_slice;
 use silk::signature::{generate_keypair, get_pubkey};
 use silk::transaction::Transaction;
 use silk::event::Event;
diff --git a/src/entry.rs b/src/entry.rs
new file mode 100644
index 0000000000..f970bc0cab
--- /dev/null
+++ b/src/entry.rs
@@ -0,0 +1,110 @@
+use hash::{extend_and_hash, hash, Sha256Hash};
+use serde::Serialize;
+use event::Event;
+
+#[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
+pub struct Entry<T> {
+    pub num_hashes: u64,
+    pub id: Sha256Hash,
+    pub event: Event<T>,
+}
+
+impl<T: Serialize> Entry<T> {
+    /// Creates a Entry from the number of hashes 'num_hashes' since the previous event
+    /// and that resulting 'id'.
+    pub fn new_tick(num_hashes: u64, id: &Sha256Hash) -> Self {
+        Entry {
+            num_hashes,
+            id: *id,
+            event: Event::Tick,
+        }
+    }
+
+    /// Verifies self.id is the result of hashing a 'start_hash' 'self.num_hashes' times.
+    /// If the event is not a Tick, then hash that as well.
+    pub fn verify(&self, start_hash: &Sha256Hash) -> bool {
+        if !self.event.verify() {
+            return false;
+        }
+        self.id == next_hash(start_hash, self.num_hashes, &self.event)
+    }
+}
+
+/// Creates the hash 'num_hashes' after start_hash. If the event contains
+/// signature, the final hash will be a hash of both the previous ID and
+/// the signature.
+pub fn next_hash<T: Serialize>(
+    start_hash: &Sha256Hash,
+    num_hashes: u64,
+    event: &Event<T>,
+) -> Sha256Hash {
+    let mut id = *start_hash;
+    let sig = event.get_signature();
+    let start_index = if sig.is_some() { 1 } else { 0 };
+    for _ in start_index..num_hashes {
+        id = hash(&id);
+    }
+    if let Some(sig) = sig {
+        id = extend_and_hash(&id, &sig);
+    }
+    id
+}
+
+/// Creates the next Entry 'num_hashes' after 'start_hash'.
+pub fn create_entry<T: Serialize>(
+    start_hash: &Sha256Hash,
+    cur_hashes: u64,
+    event: Event<T>,
+) -> Entry<T> {
+    let sig = event.get_signature();
+    let num_hashes = cur_hashes + if sig.is_some() { 1 } else { 0 };
+    let id = next_hash(start_hash, 0, &event);
+    Entry {
+        num_hashes,
+        id,
+        event,
+    }
+}
+
+/// Creates the next Tick Entry 'num_hashes' after 'start_hash'.
+pub fn create_entry_mut<T: Serialize>(
+    start_hash: &mut Sha256Hash,
+    cur_hashes: &mut u64,
+    event: Event<T>,
+) -> Entry<T> {
+    let entry = create_entry(start_hash, *cur_hashes, event);
+    *start_hash = entry.id;
+    *cur_hashes = 0;
+    entry
+}
+
+/// Creates the next Tick Entry 'num_hashes' after 'start_hash'.
+pub fn next_tick<T: Serialize>(start_hash: &Sha256Hash, num_hashes: u64) -> Entry<T> {
+    let event = Event::Tick;
+    Entry {
+        num_hashes,
+        id: next_hash(start_hash, num_hashes, &event),
+        event,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_event_verify() {
+        let zero = Sha256Hash::default();
+        let one = hash(&zero);
+        assert!(Entry::<u8>::new_tick(0, &zero).verify(&zero)); // base case
+        assert!(!Entry::<u8>::new_tick(0, &zero).verify(&one)); // base case, bad
+        assert!(next_tick::<u8>(&zero, 1).verify(&zero)); // inductive step
+        assert!(!next_tick::<u8>(&zero, 1).verify(&one)); // inductive step, bad
+    }
+
+    #[test]
+    fn test_next_tick() {
+        let zero = Sha256Hash::default();
+        assert_eq!(next_tick::<Sha256Hash>(&zero, 1).num_hashes, 1)
+    }
+}
diff --git a/src/genesis.rs b/src/genesis.rs
index 6ef4151ad2..ef9df97726 100644
--- a/src/genesis.rs
+++ b/src/genesis.rs
@@ -3,7 +3,8 @@
 use event::Event;
 use transaction::Transaction;
 use signature::{generate_keypair, get_pubkey, PublicKey};
-use log::{create_entries, Entry};
+use entry::Entry;
+use log::create_entries;
 use hash::{hash, Sha256Hash};
 use ring::rand::SystemRandom;
 use ring::signature::Ed25519KeyPair;
diff --git a/src/historian.rs b/src/historian.rs
index f0683c8f7b..7bf21d9c31 100644
--- a/src/historian.rs
+++ b/src/historian.rs
@@ -6,7 +6,7 @@ use std::collections::HashSet;
 use std::sync::mpsc::{sync_channel, Receiver, SyncSender};
 use std::time::Instant;
 use hash::{hash, Sha256Hash};
-use log::Entry;
+use entry::Entry;
 use logger::{ExitReason, Logger};
 use signature::Signature;
 use event::Event;
diff --git a/src/lib.rs b/src/lib.rs
index 4551c6833b..e452859c99 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,11 +1,12 @@
 #![cfg_attr(feature = "unstable", feature(test))]
-pub mod hash;
-pub mod log;
-pub mod logger;
-pub mod event;
-pub mod transaction;
 pub mod signature;
+pub mod hash;
+pub mod transaction;
+pub mod event;
+pub mod entry;
+pub mod log;
 pub mod genesis;
+pub mod logger;
 pub mod historian;
 pub mod accountant;
 pub mod accountant_skel;
diff --git a/src/log.rs b/src/log.rs
index 6a13f3abef..6d319c1e14 100644
--- a/src/log.rs
+++ b/src/log.rs
@@ -13,97 +13,12 @@
 /// fastest processor. Duration should therefore be estimated by assuming that the hash
 /// was generated by the fastest processor at the time the entry was logged.
 
-use hash::{extend_and_hash, hash, Sha256Hash};
+use hash::Sha256Hash;
 use serde::Serialize;
+use entry::{create_entry_mut, next_tick, Entry};
 use event::Event;
 use rayon::prelude::*;
 
-#[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
-pub struct Entry<T> {
-    pub num_hashes: u64,
-    pub id: Sha256Hash,
-    pub event: Event<T>,
-}
-
-impl<T: Serialize> Entry<T> {
-    /// Creates a Entry from the number of hashes 'num_hashes' since the previous event
-    /// and that resulting 'id'.
-    pub fn new_tick(num_hashes: u64, id: &Sha256Hash) -> Self {
-        Entry {
-            num_hashes,
-            id: *id,
-            event: Event::Tick,
-        }
-    }
-
-    /// Verifies self.id is the result of hashing a 'start_hash' 'self.num_hashes' times.
-    /// If the event is not a Tick, then hash that as well.
-    pub fn verify(&self, start_hash: &Sha256Hash) -> bool {
-        if !self.event.verify() {
-            return false;
-        }
-        self.id == next_hash(start_hash, self.num_hashes, &self.event)
-    }
-}
-
-/// Creates the hash 'num_hashes' after start_hash. If the event contains
-/// signature, the final hash will be a hash of both the previous ID and
-/// the signature.
-pub fn next_hash<T: Serialize>(
-    start_hash: &Sha256Hash,
-    num_hashes: u64,
-    event: &Event<T>,
-) -> Sha256Hash {
-    let mut id = *start_hash;
-    let sig = event.get_signature();
-    let start_index = if sig.is_some() { 1 } else { 0 };
-    for _ in start_index..num_hashes {
-        id = hash(&id);
-    }
-    if let Some(sig) = sig {
-        id = extend_and_hash(&id, &sig);
-    }
-    id
-}
-
-/// Creates the next Entry 'num_hashes' after 'start_hash'.
-pub fn create_entry<T: Serialize>(
-    start_hash: &Sha256Hash,
-    cur_hashes: u64,
-    event: Event<T>,
-) -> Entry<T> {
-    let sig = event.get_signature();
-    let num_hashes = cur_hashes + if sig.is_some() { 1 } else { 0 };
-    let id = next_hash(start_hash, 0, &event);
-    Entry {
-        num_hashes,
-        id,
-        event,
-    }
-}
-
-/// Creates the next Tick Entry 'num_hashes' after 'start_hash'.
-pub fn create_entry_mut<T: Serialize>(
-    start_hash: &mut Sha256Hash,
-    cur_hashes: &mut u64,
-    event: Event<T>,
-) -> Entry<T> {
-    let entry = create_entry(start_hash, *cur_hashes, event);
-    *start_hash = entry.id;
-    *cur_hashes = 0;
-    entry
-}
-
-/// Creates the next Tick Entry 'num_hashes' after 'start_hash'.
-pub fn next_tick<T: Serialize>(start_hash: &Sha256Hash, num_hashes: u64) -> Entry<T> {
-    let event = Event::Tick;
-    Entry {
-        num_hashes,
-        id: next_hash(start_hash, num_hashes, &event),
-        event,
-    }
-}
-
 /// Verifies the hashes and counts of a slice of events are all consistent.
 pub fn verify_slice(events: &[Entry<Sha256Hash>], start_hash: &Sha256Hash) -> bool {
     let genesis = [Entry::new_tick(Default::default(), start_hash)];
@@ -153,22 +68,7 @@ mod tests {
     use super::*;
     use signature::{generate_keypair, get_pubkey};
     use transaction::Transaction;
-
-    #[test]
-    fn test_event_verify() {
-        let zero = Sha256Hash::default();
-        let one = hash(&zero);
-        assert!(Entry::<u8>::new_tick(0, &zero).verify(&zero)); // base case
-        assert!(!Entry::<u8>::new_tick(0, &zero).verify(&one)); // base case, bad
-        assert!(next_tick::<u8>(&zero, 1).verify(&zero)); // inductive step
-        assert!(!next_tick::<u8>(&zero, 1).verify(&one)); // inductive step, bad
-    }
-
-    #[test]
-    fn test_next_tick() {
-        let zero = Sha256Hash::default();
-        assert_eq!(next_tick::<Sha256Hash>(&zero, 1).num_hashes, 1)
-    }
+    use hash::hash;
 
     fn verify_slice_generic(verify_slice: fn(&[Entry<Sha256Hash>], &Sha256Hash) -> bool) {
         let zero = Sha256Hash::default();
diff --git a/src/logger.rs b/src/logger.rs
index 8f47bc97c5..50fc1feea0 100644
--- a/src/logger.rs
+++ b/src/logger.rs
@@ -8,7 +8,7 @@
 use std::sync::mpsc::{Receiver, SyncSender, TryRecvError};
 use std::time::{Duration, Instant};
 use hash::Sha256Hash;
-use log::{create_entry_mut, Entry};
+use entry::{create_entry_mut, Entry};
 use event::Event;
 use serde::Serialize;
 use std::fmt::Debug;

From b725fdb09340aa1974d8e75827a0ccbf05bf1633 Mon Sep 17 00:00:00 2001
From: Greg Fitzgerald <garious@gmail.com>
Date: Tue, 6 Mar 2018 17:36:45 -0700
Subject: [PATCH 3/3] Sha256Hash -> Hash

Because in Loom, there's just the one. Hopefully no worries that it
shares a name with std::Hash.
---
 doc/historian.md       | 10 +++++-----
 src/accountant.rs      |  8 ++++----
 src/accountant_skel.rs |  6 +++---
 src/accountant_stub.rs | 10 +++++-----
 src/bin/demo.rs        | 13 +++++--------
 src/entry.rs           | 30 +++++++++++-------------------
 src/genesis.rs         |  4 ++--
 src/hash.rs            |  6 +++---
 src/historian.rs       | 14 +++++++-------
 src/log.rs             | 23 ++++++++++-------------
 src/logger.rs          |  6 +++---
 src/transaction.rs     | 19 +++++++------------
 12 files changed, 65 insertions(+), 84 deletions(-)

diff --git a/doc/historian.md b/doc/historian.md
index 8351645688..4f29267e02 100644
--- a/doc/historian.md
+++ b/doc/historian.md
@@ -11,15 +11,15 @@ with by verifying each entry's hash can be generated from the hash in the previo
 extern crate silk;
 
 use silk::historian::Historian;
-use silk::log::{verify_slice, Entry, Sha256Hash};
+use silk::log::{verify_slice, Entry, Hash};
 use silk::event::{generate_keypair, get_pubkey, sign_claim_data, Event};
 use std::thread::sleep;
 use std::time::Duration;
 use std::sync::mpsc::SendError;
 
-fn create_log(hist: &Historian<Sha256Hash>) -> Result<(), SendError<Event<Sha256Hash>>> {
+fn create_log(hist: &Historian<Hash>) -> Result<(), SendError<Event<Hash>>> {
     sleep(Duration::from_millis(15));
-    let asset = Sha256Hash::default();
+    let asset = Hash::default();
     let keypair = generate_keypair();
     let event0 = Event::new_claim(get_pubkey(&keypair), asset, sign_claim_data(&asset, &keypair));
     hist.sender.send(event0)?;
@@ -28,11 +28,11 @@ fn create_log(hist: &Historian<Sha256Hash>) -> Result<(), SendError<Event<Sha256
 }
 
 fn main() {
-    let seed = Sha256Hash::default();
+    let seed = Hash::default();
     let hist = Historian::new(&seed, Some(10));
     create_log(&hist).expect("send error");
     drop(hist.sender);
-    let entries: Vec<Entry<Sha256Hash>> = hist.receiver.iter().collect();
+    let entries: Vec<Entry<Hash>> = hist.receiver.iter().collect();
     for entry in &entries {
         println!("{:?}", entry);
     }
diff --git a/src/accountant.rs b/src/accountant.rs
index 0bc97f5a68..96bbb03366 100644
--- a/src/accountant.rs
+++ b/src/accountant.rs
@@ -2,7 +2,7 @@
 //! event log to record transactions. Its users can deposit funds and
 //! transfer funds to other users.
 
-use hash::Sha256Hash;
+use hash::Hash;
 use entry::Entry;
 use event::Event;
 use transaction::Transaction;
@@ -27,8 +27,8 @@ pub type Result<T> = result::Result<T, AccountingError>;
 pub struct Accountant {
     pub historian: Historian<i64>,
     pub balances: HashMap<PublicKey, i64>,
-    pub first_id: Sha256Hash,
-    pub last_id: Sha256Hash,
+    pub first_id: Hash,
+    pub last_id: Hash,
 }
 
 impl Accountant {
@@ -67,7 +67,7 @@ impl Accountant {
         Self::new_from_entries(gen.create_entries(), ms_per_tick)
     }
 
-    pub fn sync(self: &mut Self) -> Sha256Hash {
+    pub fn sync(self: &mut Self) -> Hash {
         while let Ok(entry) = self.historian.receiver.try_recv() {
             self.last_id = entry.id;
         }
diff --git a/src/accountant_skel.rs b/src/accountant_skel.rs
index 9cd25dad08..c5afe6bc7b 100644
--- a/src/accountant_skel.rs
+++ b/src/accountant_skel.rs
@@ -2,7 +2,7 @@ use std::io;
 use accountant::Accountant;
 use transaction::Transaction;
 use signature::PublicKey;
-use hash::Sha256Hash;
+use hash::Hash;
 use entry::Entry;
 use std::net::UdpSocket;
 use bincode::{deserialize, serialize};
@@ -15,7 +15,7 @@ pub struct AccountantSkel {
 pub enum Request {
     Transaction(Transaction<i64>),
     GetBalance { key: PublicKey },
-    GetEntries { last_id: Sha256Hash },
+    GetEntries { last_id: Hash },
     GetId { is_last: bool },
 }
 
@@ -23,7 +23,7 @@ pub enum Request {
 pub enum Response {
     Balance { key: PublicKey, val: Option<i64> },
     Entries { entries: Vec<Entry<i64>> },
-    Id { id: Sha256Hash, is_last: bool },
+    Id { id: Hash, is_last: bool },
 }
 
 impl AccountantSkel {
diff --git a/src/accountant_stub.rs b/src/accountant_stub.rs
index 61529642ae..f36e940480 100644
--- a/src/accountant_stub.rs
+++ b/src/accountant_stub.rs
@@ -7,7 +7,7 @@ use std::io;
 use bincode::{deserialize, serialize};
 use transaction::Transaction;
 use signature::{PublicKey, Signature};
-use hash::Sha256Hash;
+use hash::Hash;
 use entry::Entry;
 use ring::signature::Ed25519KeyPair;
 use accountant_skel::{Request, Response};
@@ -15,7 +15,7 @@ use accountant_skel::{Request, Response};
 pub struct AccountantStub {
     pub addr: String,
     pub socket: UdpSocket,
-    pub last_id: Option<Sha256Hash>,
+    pub last_id: Option<Hash>,
 }
 
 impl AccountantStub {
@@ -38,7 +38,7 @@ impl AccountantStub {
         n: i64,
         keypair: &Ed25519KeyPair,
         to: PublicKey,
-        last_id: &Sha256Hash,
+        last_id: &Hash,
     ) -> io::Result<Signature> {
         let tr = Transaction::new(keypair, to, n, *last_id);
         let sig = tr.sig;
@@ -59,7 +59,7 @@ impl AccountantStub {
         Ok(None)
     }
 
-    fn get_id(&self, is_last: bool) -> io::Result<Sha256Hash> {
+    fn get_id(&self, is_last: bool) -> io::Result<Hash> {
         let req = Request::GetId { is_last };
         let data = serialize(&req).expect("serialize GetId");
         self.socket.send_to(&data, &self.addr)?;
@@ -72,7 +72,7 @@ impl AccountantStub {
         Ok(Default::default())
     }
 
-    pub fn get_last_id(&self) -> io::Result<Sha256Hash> {
+    pub fn get_last_id(&self) -> io::Result<Hash> {
         self.get_id(true)
     }
 
diff --git a/src/bin/demo.rs b/src/bin/demo.rs
index 75614d56a1..4aad34f20c 100644
--- a/src/bin/demo.rs
+++ b/src/bin/demo.rs
@@ -1,7 +1,7 @@
 extern crate silk;
 
 use silk::historian::Historian;
-use silk::hash::Sha256Hash;
+use silk::hash::Hash;
 use silk::entry::Entry;
 use silk::log::verify_slice;
 use silk::signature::{generate_keypair, get_pubkey};
@@ -11,12 +11,9 @@ use std::thread::sleep;
 use std::time::Duration;
 use std::sync::mpsc::SendError;
 
-fn create_log(
-    hist: &Historian<Sha256Hash>,
-    seed: &Sha256Hash,
-) -> Result<(), SendError<Event<Sha256Hash>>> {
+fn create_log(hist: &Historian<Hash>, seed: &Hash) -> Result<(), SendError<Event<Hash>>> {
     sleep(Duration::from_millis(15));
-    let asset = Sha256Hash::default();
+    let asset = Hash::default();
     let keypair = generate_keypair();
     let tr = Transaction::new(&keypair, get_pubkey(&keypair), asset, *seed);
     let event0 = Event::Transaction(tr);
@@ -26,11 +23,11 @@ fn create_log(
 }
 
 fn main() {
-    let seed = Sha256Hash::default();
+    let seed = Hash::default();
     let hist = Historian::new(&seed, Some(10));
     create_log(&hist, &seed).expect("send error");
     drop(hist.sender);
-    let entries: Vec<Entry<Sha256Hash>> = hist.receiver.iter().collect();
+    let entries: Vec<Entry<Hash>> = hist.receiver.iter().collect();
     for entry in &entries {
         println!("{:?}", entry);
     }
diff --git a/src/entry.rs b/src/entry.rs
index f970bc0cab..82b691087b 100644
--- a/src/entry.rs
+++ b/src/entry.rs
@@ -1,18 +1,18 @@
-use hash::{extend_and_hash, hash, Sha256Hash};
+use hash::{extend_and_hash, hash, Hash};
 use serde::Serialize;
 use event::Event;
 
 #[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
 pub struct Entry<T> {
     pub num_hashes: u64,
-    pub id: Sha256Hash,
+    pub id: Hash,
     pub event: Event<T>,
 }
 
 impl<T: Serialize> Entry<T> {
     /// Creates a Entry from the number of hashes 'num_hashes' since the previous event
     /// and that resulting 'id'.
-    pub fn new_tick(num_hashes: u64, id: &Sha256Hash) -> Self {
+    pub fn new_tick(num_hashes: u64, id: &Hash) -> Self {
         Entry {
             num_hashes,
             id: *id,
@@ -22,7 +22,7 @@ impl<T: Serialize> Entry<T> {
 
     /// Verifies self.id is the result of hashing a 'start_hash' 'self.num_hashes' times.
     /// If the event is not a Tick, then hash that as well.
-    pub fn verify(&self, start_hash: &Sha256Hash) -> bool {
+    pub fn verify(&self, start_hash: &Hash) -> bool {
         if !self.event.verify() {
             return false;
         }
@@ -33,11 +33,7 @@ impl<T: Serialize> Entry<T> {
 /// Creates the hash 'num_hashes' after start_hash. If the event contains
 /// signature, the final hash will be a hash of both the previous ID and
 /// the signature.
-pub fn next_hash<T: Serialize>(
-    start_hash: &Sha256Hash,
-    num_hashes: u64,
-    event: &Event<T>,
-) -> Sha256Hash {
+pub fn next_hash<T: Serialize>(start_hash: &Hash, num_hashes: u64, event: &Event<T>) -> Hash {
     let mut id = *start_hash;
     let sig = event.get_signature();
     let start_index = if sig.is_some() { 1 } else { 0 };
@@ -51,11 +47,7 @@ pub fn next_hash<T: Serialize>(
 }
 
 /// Creates the next Entry 'num_hashes' after 'start_hash'.
-pub fn create_entry<T: Serialize>(
-    start_hash: &Sha256Hash,
-    cur_hashes: u64,
-    event: Event<T>,
-) -> Entry<T> {
+pub fn create_entry<T: Serialize>(start_hash: &Hash, cur_hashes: u64, event: Event<T>) -> Entry<T> {
     let sig = event.get_signature();
     let num_hashes = cur_hashes + if sig.is_some() { 1 } else { 0 };
     let id = next_hash(start_hash, 0, &event);
@@ -68,7 +60,7 @@ pub fn create_entry<T: Serialize>(
 
 /// Creates the next Tick Entry 'num_hashes' after 'start_hash'.
 pub fn create_entry_mut<T: Serialize>(
-    start_hash: &mut Sha256Hash,
+    start_hash: &mut Hash,
     cur_hashes: &mut u64,
     event: Event<T>,
 ) -> Entry<T> {
@@ -79,7 +71,7 @@ pub fn create_entry_mut<T: Serialize>(
 }
 
 /// Creates the next Tick Entry 'num_hashes' after 'start_hash'.
-pub fn next_tick<T: Serialize>(start_hash: &Sha256Hash, num_hashes: u64) -> Entry<T> {
+pub fn next_tick<T: Serialize>(start_hash: &Hash, num_hashes: u64) -> Entry<T> {
     let event = Event::Tick;
     Entry {
         num_hashes,
@@ -94,7 +86,7 @@ mod tests {
 
     #[test]
     fn test_event_verify() {
-        let zero = Sha256Hash::default();
+        let zero = Hash::default();
         let one = hash(&zero);
         assert!(Entry::<u8>::new_tick(0, &zero).verify(&zero)); // base case
         assert!(!Entry::<u8>::new_tick(0, &zero).verify(&one)); // base case, bad
@@ -104,7 +96,7 @@ mod tests {
 
     #[test]
     fn test_next_tick() {
-        let zero = Sha256Hash::default();
-        assert_eq!(next_tick::<Sha256Hash>(&zero, 1).num_hashes, 1)
+        let zero = Hash::default();
+        assert_eq!(next_tick::<Hash>(&zero, 1).num_hashes, 1)
     }
 }
diff --git a/src/genesis.rs b/src/genesis.rs
index ef9df97726..4d95e24eb6 100644
--- a/src/genesis.rs
+++ b/src/genesis.rs
@@ -5,7 +5,7 @@ use transaction::Transaction;
 use signature::{generate_keypair, get_pubkey, PublicKey};
 use entry::Entry;
 use log::create_entries;
-use hash::{hash, Sha256Hash};
+use hash::{hash, Hash};
 use ring::rand::SystemRandom;
 use ring::signature::Ed25519KeyPair;
 use untrusted::Input;
@@ -44,7 +44,7 @@ impl Genesis {
         }
     }
 
-    pub fn get_seed(&self) -> Sha256Hash {
+    pub fn get_seed(&self) -> Hash {
         hash(&self.pkcs8)
     }
 
diff --git a/src/hash.rs b/src/hash.rs
index 5efb933f5f..181db33499 100644
--- a/src/hash.rs
+++ b/src/hash.rs
@@ -2,17 +2,17 @@ use generic_array::GenericArray;
 use generic_array::typenum::U32;
 use sha2::{Digest, Sha256};
 
-pub type Sha256Hash = GenericArray<u8, U32>;
+pub type Hash = GenericArray<u8, U32>;
 
 /// Return a Sha256 hash for the given data.
-pub fn hash(val: &[u8]) -> Sha256Hash {
+pub fn hash(val: &[u8]) -> Hash {
     let mut hasher = Sha256::default();
     hasher.input(val);
     hasher.result()
 }
 
 /// Return the hash of the given hash extended with the given value.
-pub fn extend_and_hash(id: &Sha256Hash, val: &[u8]) -> Sha256Hash {
+pub fn extend_and_hash(id: &Hash, val: &[u8]) -> Hash {
     let mut hash_data = id.to_vec();
     hash_data.extend_from_slice(val);
     hash(&hash_data)
diff --git a/src/historian.rs b/src/historian.rs
index 7bf21d9c31..6d335819e0 100644
--- a/src/historian.rs
+++ b/src/historian.rs
@@ -5,7 +5,7 @@ use std::thread::{spawn, JoinHandle};
 use std::collections::HashSet;
 use std::sync::mpsc::{sync_channel, Receiver, SyncSender};
 use std::time::Instant;
-use hash::{hash, Sha256Hash};
+use hash::{hash, Hash};
 use entry::Entry;
 use logger::{ExitReason, Logger};
 use signature::Signature;
@@ -21,7 +21,7 @@ pub struct Historian<T> {
 }
 
 impl<T: 'static + Serialize + Clone + Debug + Send> Historian<T> {
-    pub fn new(start_hash: &Sha256Hash, ms_per_tick: Option<u64>) -> Self {
+    pub fn new(start_hash: &Hash, ms_per_tick: Option<u64>) -> Self {
         let (sender, event_receiver) = sync_channel(1000);
         let (entry_sender, receiver) = sync_channel(1000);
         let thread_hdl =
@@ -38,7 +38,7 @@ impl<T: 'static + Serialize + Clone + Debug + Send> Historian<T> {
     /// A background thread that will continue tagging received Event messages and
     /// sending back Entry messages until either the receiver or sender channel is closed.
     fn create_logger(
-        start_hash: Sha256Hash,
+        start_hash: Hash,
         ms_per_tick: Option<u64>,
         receiver: Receiver<Event<T>>,
         sender: SyncSender<Entry<T>>,
@@ -75,7 +75,7 @@ mod tests {
 
     #[test]
     fn test_historian() {
-        let zero = Sha256Hash::default();
+        let zero = Hash::default();
         let hist = Historian::new(&zero, None);
 
         hist.sender.send(Event::Tick).unwrap();
@@ -99,7 +99,7 @@ mod tests {
 
     #[test]
     fn test_historian_closed_sender() {
-        let zero = Sha256Hash::default();
+        let zero = Hash::default();
         let hist = Historian::<u8>::new(&zero, None);
         drop(hist.receiver);
         hist.sender.send(Event::Tick).unwrap();
@@ -119,12 +119,12 @@ mod tests {
 
     #[test]
     fn test_ticking_historian() {
-        let zero = Sha256Hash::default();
+        let zero = Hash::default();
         let hist = Historian::new(&zero, Some(20));
         sleep(Duration::from_millis(30));
         hist.sender.send(Event::Tick).unwrap();
         drop(hist.sender);
-        let entries: Vec<Entry<Sha256Hash>> = hist.receiver.iter().collect();
+        let entries: Vec<Entry<Hash>> = hist.receiver.iter().collect();
 
         // Ensure one entry is sent back for each tick sent in.
         assert_eq!(entries.len(), 1);
diff --git a/src/log.rs b/src/log.rs
index 6d319c1e14..78f287c742 100644
--- a/src/log.rs
+++ b/src/log.rs
@@ -13,37 +13,34 @@
 /// fastest processor. Duration should therefore be estimated by assuming that the hash
 /// was generated by the fastest processor at the time the entry was logged.
 
-use hash::Sha256Hash;
+use hash::Hash;
 use serde::Serialize;
 use entry::{create_entry_mut, next_tick, Entry};
 use event::Event;
 use rayon::prelude::*;
 
 /// Verifies the hashes and counts of a slice of events are all consistent.
-pub fn verify_slice(events: &[Entry<Sha256Hash>], start_hash: &Sha256Hash) -> bool {
+pub fn verify_slice(events: &[Entry<Hash>], start_hash: &Hash) -> bool {
     let genesis = [Entry::new_tick(Default::default(), start_hash)];
     let event_pairs = genesis.par_iter().chain(events).zip(events);
     event_pairs.all(|(x0, x1)| x1.verify(&x0.id))
 }
 
 /// Verifies the hashes and counts of a slice of events are all consistent.
-pub fn verify_slice_i64(events: &[Entry<i64>], start_hash: &Sha256Hash) -> bool {
+pub fn verify_slice_i64(events: &[Entry<i64>], start_hash: &Hash) -> bool {
     let genesis = [Entry::new_tick(Default::default(), start_hash)];
     let event_pairs = genesis.par_iter().chain(events).zip(events);
     event_pairs.all(|(x0, x1)| x1.verify(&x0.id))
 }
 
 /// Verifies the hashes and events serially. Exists only for reference.
-pub fn verify_slice_seq<T: Serialize>(events: &[Entry<T>], start_hash: &Sha256Hash) -> bool {
+pub fn verify_slice_seq<T: Serialize>(events: &[Entry<T>], start_hash: &Hash) -> bool {
     let genesis = [Entry::new_tick(0, start_hash)];
     let mut event_pairs = genesis.iter().chain(events).zip(events);
     event_pairs.all(|(x0, x1)| x1.verify(&x0.id))
 }
 
-pub fn create_entries<T: Serialize>(
-    start_hash: &Sha256Hash,
-    events: Vec<Event<T>>,
-) -> Vec<Entry<T>> {
+pub fn create_entries<T: Serialize>(start_hash: &Hash, events: Vec<Event<T>>) -> Vec<Entry<T>> {
     let mut id = *start_hash;
     events
         .into_iter()
@@ -52,7 +49,7 @@ pub fn create_entries<T: Serialize>(
 }
 
 /// Create a vector of Ticks of length 'len' from 'start_hash' hash and 'num_hashes'.
-pub fn next_ticks(start_hash: &Sha256Hash, num_hashes: u64, len: usize) -> Vec<Entry<Sha256Hash>> {
+pub fn next_ticks(start_hash: &Hash, num_hashes: u64, len: usize) -> Vec<Entry<Hash>> {
     let mut id = *start_hash;
     let mut ticks = vec![];
     for _ in 0..len {
@@ -70,8 +67,8 @@ mod tests {
     use transaction::Transaction;
     use hash::hash;
 
-    fn verify_slice_generic(verify_slice: fn(&[Entry<Sha256Hash>], &Sha256Hash) -> bool) {
-        let zero = Sha256Hash::default();
+    fn verify_slice_generic(verify_slice: fn(&[Entry<Hash>], &Hash) -> bool) {
+        let zero = Hash::default();
         let one = hash(&zero);
         assert!(verify_slice(&vec![], &zero)); // base case
         assert!(verify_slice(&vec![Entry::new_tick(0, &zero)], &zero)); // singleton case 1
@@ -90,12 +87,12 @@ mod tests {
 
     #[test]
     fn test_verify_slice_seq() {
-        verify_slice_generic(verify_slice_seq::<Sha256Hash>);
+        verify_slice_generic(verify_slice_seq::<Hash>);
     }
 
     #[test]
     fn test_reorder_attack() {
-        let zero = Sha256Hash::default();
+        let zero = Hash::default();
         let one = hash(&zero);
 
         // First, verify entries
diff --git a/src/logger.rs b/src/logger.rs
index 50fc1feea0..2d839809a0 100644
--- a/src/logger.rs
+++ b/src/logger.rs
@@ -7,7 +7,7 @@
 
 use std::sync::mpsc::{Receiver, SyncSender, TryRecvError};
 use std::time::{Duration, Instant};
-use hash::Sha256Hash;
+use hash::Hash;
 use entry::{create_entry_mut, Entry};
 use event::Event;
 use serde::Serialize;
@@ -23,7 +23,7 @@ pub enum ExitReason {
 pub struct Logger<T> {
     pub sender: SyncSender<Entry<T>>,
     pub receiver: Receiver<Event<T>>,
-    pub last_id: Sha256Hash,
+    pub last_id: Hash,
     pub num_hashes: u64,
     pub num_ticks: u64,
 }
@@ -32,7 +32,7 @@ impl<T: Serialize + Clone + Debug> Logger<T> {
     pub fn new(
         receiver: Receiver<Event<T>>,
         sender: SyncSender<Entry<T>>,
-        start_hash: Sha256Hash,
+        start_hash: Hash,
     ) -> Self {
         Logger {
             receiver,
diff --git a/src/transaction.rs b/src/transaction.rs
index 1193358668..209a5dc7cb 100644
--- a/src/transaction.rs
+++ b/src/transaction.rs
@@ -4,24 +4,19 @@ use signature::{get_pubkey, verify_signature, PublicKey, Signature};
 use ring::signature::Ed25519KeyPair;
 use serde::Serialize;
 use bincode::serialize;
-use hash::Sha256Hash;
+use hash::Hash;
 
 #[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
 pub struct Transaction<T> {
     pub from: PublicKey,
     pub to: PublicKey,
     pub asset: T,
-    pub last_id: Sha256Hash,
+    pub last_id: Hash,
     pub sig: Signature,
 }
 
 impl<T: Serialize> Transaction<T> {
-    pub fn new(
-        from_keypair: &Ed25519KeyPair,
-        to: PublicKey,
-        asset: T,
-        last_id: Sha256Hash,
-    ) -> Self {
+    pub fn new(from_keypair: &Ed25519KeyPair, to: PublicKey, asset: T, last_id: Hash) -> Self {
         let mut tr = Transaction {
             from: get_pubkey(&from_keypair),
             to,
@@ -58,14 +53,14 @@ mod tests {
     fn test_claim() {
         let keypair = generate_keypair();
         let asset = hash(b"hello, world");
-        let zero = Sha256Hash::default();
+        let zero = Hash::default();
         let tr0 = Transaction::new(&keypair, get_pubkey(&keypair), asset, zero);
         assert!(tr0.verify());
     }
 
     #[test]
     fn test_transfer() {
-        let zero = Sha256Hash::default();
+        let zero = Hash::default();
         let keypair0 = generate_keypair();
         let keypair1 = generate_keypair();
         let pubkey1 = get_pubkey(&keypair1);
@@ -90,7 +85,7 @@ mod tests {
 
     #[test]
     fn test_bad_event_signature() {
-        let zero = Sha256Hash::default();
+        let zero = Hash::default();
         let keypair = generate_keypair();
         let pubkey = get_pubkey(&keypair);
         let mut tr = Transaction::new(&keypair, pubkey, hash(b"hello, world"), zero);
@@ -105,7 +100,7 @@ mod tests {
         let keypair1 = generate_keypair();
         let thief_keypair = generate_keypair();
         let pubkey1 = get_pubkey(&keypair1);
-        let zero = Sha256Hash::default();
+        let zero = Hash::default();
         let mut tr = Transaction::new(&keypair0, pubkey1, hash(b"hello, world"), zero);
         tr.sign(&keypair0);
         tr.to = get_pubkey(&thief_keypair); // <-- attack!