diff --git a/.travis.yml b/.travis.yml
index 9ee3205fc445df..da4cd01db386af 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,7 +9,7 @@ matrix:
   - rust: stable
   - rust: nightly
     env:
-    - FEATURES='unstable'
+    - FEATURES='asm,unstable'
 before_script: |
   export PATH="$PATH:$HOME/.cargo/bin"
   rustup component add rustfmt-preview
diff --git a/Cargo.toml b/Cargo.toml
index 0f6900c6b48283..21fc26483eb0e3 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -20,7 +20,11 @@ codecov = { repository = "loomprotocol/silk", branch = "master", service = "gith
 
 [features]
 unstable = []
+asm = ["sha2-asm"]
 
 [dependencies]
 rayon = "1.0.0"
 itertools = "0.7.6"
+sha2 = "0.7.0"
+sha2-asm = {version="0.3", optional=true}
+digest = "0.7.2"
diff --git a/src/bin/demo.rs b/src/bin/demo.rs
index 4715d2e0837fab..962781e3f1a81e 100644
--- a/src/bin/demo.rs
+++ b/src/bin/demo.rs
@@ -1,7 +1,7 @@
 extern crate silk;
 
 use silk::historian::Historian;
-use silk::log::{verify_slice, Entry, Event};
+use silk::log::{verify_slice, Entry, Event, Sha256Hash};
 use std::{thread, time};
 use std::sync::mpsc::SendError;
 
@@ -15,13 +15,13 @@ fn create_log(hist: &Historian) -> Result<(), SendError<Event>> {
 }
 
 fn main() {
-    let seed = 0;
-    let hist = Historian::new(seed);
+    let seed = Sha256Hash::default();
+    let hist = Historian::new(&seed);
     create_log(&hist).expect("send error");
     drop(hist.sender);
     let entries: Vec<Entry> = hist.receiver.iter().collect();
     for entry in &entries {
         println!("{:?}", entry);
     }
-    assert!(verify_slice(&entries, seed));
+    assert!(verify_slice(&entries, &seed));
 }
diff --git a/src/historian.rs b/src/historian.rs
index d0a282589f998c..8f410e4a80e0aa 100644
--- a/src/historian.rs
+++ b/src/historian.rs
@@ -7,7 +7,7 @@
 
 use std::thread::JoinHandle;
 use std::sync::mpsc::{Receiver, Sender};
-use log::{hash, Entry, Event};
+use log::{hash, Entry, Event, Sha256Hash};
 
 pub struct Historian {
     pub sender: Sender<Event>,
@@ -25,7 +25,7 @@ fn log_events(
     receiver: &Receiver<Event>,
     sender: &Sender<Entry>,
     num_hashes: u64,
-    end_hash: u64,
+    end_hash: Sha256Hash,
 ) -> Result<u64, (Entry, ExitReason)> {
     use std::sync::mpsc::TryRecvError;
     let mut num_hashes = num_hashes;
@@ -60,7 +60,7 @@ fn log_events(
 /// A background thread that will continue tagging received Event messages and
 /// sending back Entry messages until either the receiver or sender channel is closed.
 pub fn create_logger(
-    start_hash: u64,
+    start_hash: Sha256Hash,
     receiver: Receiver<Event>,
     sender: Sender<Entry>,
 ) -> JoinHandle<(Entry, ExitReason)> {
@@ -73,18 +73,18 @@ pub fn create_logger(
                 Ok(n) => num_hashes = n,
                 Err(err) => return err,
             }
-            end_hash = hash(end_hash);
+            end_hash = hash(&end_hash);
             num_hashes += 1;
         }
     })
 }
 
 impl Historian {
-    pub fn new(start_hash: u64) -> Self {
+    pub fn new(start_hash: &Sha256Hash) -> Self {
         use std::sync::mpsc::channel;
         let (sender, event_receiver) = channel();
         let (entry_sender, receiver) = channel();
-        let thread_hdl = create_logger(start_hash, event_receiver, entry_sender);
+        let thread_hdl = create_logger(*start_hash, event_receiver, entry_sender);
         Historian {
             sender,
             receiver,
@@ -103,7 +103,8 @@ mod tests {
         use std::thread::sleep;
         use std::time::Duration;
 
-        let hist = Historian::new(0);
+        let zero = Sha256Hash::default();
+        let hist = Historian::new(&zero);
 
         hist.sender.send(Event::Tick).unwrap();
         sleep(Duration::new(0, 1_000_000));
@@ -121,12 +122,13 @@ mod tests {
             ExitReason::RecvDisconnected
         );
 
-        assert!(verify_slice(&[entry0, entry1, entry2], 0));
+        assert!(verify_slice(&[entry0, entry1, entry2], &zero));
     }
 
     #[test]
     fn test_historian_closed_sender() {
-        let hist = Historian::new(0);
+        let zero = Sha256Hash::default();
+        let hist = Historian::new(&zero);
         drop(hist.receiver);
         hist.sender.send(Event::Tick).unwrap();
         assert_eq!(
diff --git a/src/lib.rs b/src/lib.rs
index f6952625a8539a..5087d40cf7c575 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,5 +1,7 @@
 #![cfg_attr(feature = "unstable", feature(test))]
 pub mod log;
 pub mod historian;
+extern crate digest;
 extern crate itertools;
 extern crate rayon;
+extern crate sha2;
diff --git a/src/log.rs b/src/log.rs
index 5db5437e2877d2..4eef7852697546 100644
--- a/src/log.rs
+++ b/src/log.rs
@@ -12,10 +12,15 @@
 /// Though processing power varies across nodes, the network gives priority to the
 /// 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 digest::generic_array::GenericArray;
+use digest::generic_array::typenum::U32;
+pub type Sha256Hash = GenericArray<u8, U32>;
+
 #[derive(Debug, PartialEq, Eq, Clone)]
 pub struct Entry {
     pub num_hashes: u64,
-    pub end_hash: u64,
+    pub end_hash: Sha256Hash,
     pub event: Event,
 }
 
@@ -33,58 +38,57 @@ pub enum Event {
 impl Entry {
     /// Creates a Entry from the number of hashes 'num_hashes' since the previous event
     /// and that resulting 'end_hash'.
-    pub fn new_tick(num_hashes: u64, end_hash: u64) -> Self {
+    pub fn new_tick(num_hashes: u64, end_hash: &Sha256Hash) -> Self {
         let event = Event::Tick;
         Entry {
             num_hashes,
-            end_hash,
+            end_hash: *end_hash,
             event,
         }
     }
 
     /// Verifies self.end_hash is the result of hashing a 'start_hash' 'self.num_hashes' times.
-    pub fn verify(self: &Self, start_hash: u64) -> bool {
+    pub fn verify(self: &Self, start_hash: &Sha256Hash) -> bool {
         self.end_hash == next_tick(start_hash, self.num_hashes).end_hash
     }
 }
 
-pub fn hash(val: u64) -> u64 {
-    use std::collections::hash_map::DefaultHasher;
-    use std::hash::{Hash, Hasher};
-    let mut hasher = DefaultHasher::new();
-    val.hash(&mut hasher);
-    hasher.finish()
+pub fn hash(val: &[u8]) -> Sha256Hash {
+    use sha2::{Digest, Sha256};
+    let mut hasher = Sha256::default();
+    hasher.input(val);
+    hasher.result()
 }
 
 /// Creates the next Tick Entry 'num_hashes' after 'start_hash'.
-pub fn next_tick(start_hash: u64, num_hashes: u64) -> Entry {
-    let mut end_hash = start_hash;
+pub fn next_tick(start_hash: &Sha256Hash, num_hashes: u64) -> Entry {
+    let mut end_hash = *start_hash;
     for _ in 0..num_hashes {
-        end_hash = hash(end_hash);
+        end_hash = hash(&end_hash);
     }
-    Entry::new_tick(num_hashes, end_hash)
+    Entry::new_tick(num_hashes, &end_hash)
 }
 
 /// Verifies the hashes and counts of a slice of events are all consistent.
-pub fn verify_slice(events: &[Entry], start_hash: u64) -> bool {
+pub fn verify_slice(events: &[Entry], start_hash: &Sha256Hash) -> bool {
     use rayon::prelude::*;
-    let genesis = [Entry::new_tick(0, start_hash)];
+    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.end_hash))
+    event_pairs.all(|(x0, x1)| x1.verify(&x0.end_hash))
 }
 
 /// Verifies the hashes and events serially. Exists only for reference.
-pub fn verify_slice_seq(events: &[Entry], start_hash: u64) -> bool {
+pub fn verify_slice_seq(events: &[Entry], start_hash: &Sha256Hash) -> 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.end_hash))
+    event_pairs.all(|(x0, x1)| x1.verify(&x0.end_hash))
 }
 
 /// Create a vector of Ticks of length 'len' from 'start_hash' hash and 'num_hashes'.
-pub fn create_ticks(start_hash: u64, num_hashes: u64, len: usize) -> Vec<Entry> {
+pub fn create_ticks(start_hash: &Sha256Hash, num_hashes: u64, len: usize) -> Vec<Entry> {
     use itertools::unfold;
-    let mut events = unfold(start_hash, |state| {
-        let event = next_tick(*state, num_hashes);
+    let mut events = unfold(*start_hash, |state| {
+        let event = next_tick(state, num_hashes);
         *state = event.end_hash;
         return Some(event);
     });
@@ -97,26 +101,31 @@ mod tests {
 
     #[test]
     fn test_event_verify() {
-        assert!(Entry::new_tick(0, 0).verify(0)); // base case
-        assert!(!Entry::new_tick(0, 0).verify(1)); // base case, bad
-        assert!(next_tick(0, 1).verify(0)); // inductive step
-        assert!(!next_tick(0, 1).verify(1)); // inductive step, bad
+        let zero = Sha256Hash::default();
+        let one = hash(&zero);
+        assert!(Entry::new_tick(0, &zero).verify(&zero)); // base case
+        assert!(!Entry::new_tick(0, &zero).verify(&one)); // base case, bad
+        assert!(next_tick(&zero, 1).verify(&zero)); // inductive step
+        assert!(!next_tick(&zero, 1).verify(&one)); // inductive step, bad
     }
 
     #[test]
     fn test_next_tick() {
-        assert_eq!(next_tick(0, 1).num_hashes, 1)
+        let zero = Sha256Hash::default();
+        assert_eq!(next_tick(&zero, 1).num_hashes, 1)
     }
 
-    fn verify_slice_generic(verify_slice: fn(&[Entry], u64) -> bool) {
-        assert!(verify_slice(&vec![], 0)); // base case
-        assert!(verify_slice(&vec![Entry::new_tick(0, 0)], 0)); // singleton case 1
-        assert!(!verify_slice(&vec![Entry::new_tick(0, 0)], 1)); // singleton case 2, bad
-        assert!(verify_slice(&create_ticks(0, 0, 2), 0)); // inductive step
-
-        let mut bad_ticks = create_ticks(0, 0, 2);
-        bad_ticks[1].end_hash = 1;
-        assert!(!verify_slice(&bad_ticks, 0)); // inductive step, bad
+    fn verify_slice_generic(verify_slice: fn(&[Entry], &Sha256Hash) -> bool) {
+        let zero = Sha256Hash::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
+        assert!(!verify_slice(&vec![Entry::new_tick(0, &zero)], &one)); // singleton case 2, bad
+        assert!(verify_slice(&create_ticks(&zero, 0, 2), &zero)); // inductive step
+
+        let mut bad_ticks = create_ticks(&zero, 0, 2);
+        bad_ticks[1].end_hash = one;
+        assert!(!verify_slice(&bad_ticks, &zero)); // inductive step, bad
     }
 
     #[test]
@@ -139,19 +148,19 @@ mod bench {
 
     #[bench]
     fn event_bench(bencher: &mut Bencher) {
-        let start_hash = 0;
-        let events = create_ticks(start_hash, 100_000, 8);
+        let start_hash = Default::default();
+        let events = create_ticks(&start_hash, 100_000, 8);
         bencher.iter(|| {
-            assert!(verify_slice(&events, start_hash));
+            assert!(verify_slice(&events, &start_hash));
         });
     }
 
     #[bench]
     fn event_bench_seq(bencher: &mut Bencher) {
-        let start_hash = 0;
-        let events = create_ticks(start_hash, 100_000, 8);
+        let start_hash = Default::default();
+        let events = create_ticks(&start_hash, 100_000, 8);
         bencher.iter(|| {
-            assert!(verify_slice_seq(&events, start_hash));
+            assert!(verify_slice_seq(&events, &start_hash));
         });
     }
 }