diff --git a/eth2/utils/ssz/src/cached_tree_hash.rs b/eth2/utils/ssz/src/cached_tree_hash.rs
new file mode 100644
index 000000000..7a5b1c527
--- /dev/null
+++ b/eth2/utils/ssz/src/cached_tree_hash.rs
@@ -0,0 +1,331 @@
+use crate::ssz_encode;
+use hashing::hash;
+
+const BYTES_PER_CHUNK: usize = 32;
+const HASHSIZE: usize = 32;
+const MERKLE_HASH_CHUNCK: usize = 2 * BYTES_PER_CHUNK;
+
+pub trait CachedTreeHash {
+    fn cached_hash_tree_root(
+        &self,
+        other: &Self,
+        cache: &mut [u8],
+        i: usize,
+        changes: Vec<bool>,
+    ) -> Option<(usize, Vec<bool>)>;
+}
+
+impl CachedTreeHash for u64 {
+    fn cached_hash_tree_root(
+        &self,
+        other: &Self,
+        cache: &mut [u8],
+        i: usize,
+        mut changes: Vec<bool>,
+    ) -> Option<(usize, Vec<bool>)> {
+        if self != other {
+            cache
+                .get_mut(i..i + HASHSIZE)?
+                .copy_from_slice(&mut hash(&ssz_encode(self)));
+            changes.push(true);
+        } else {
+            changes.push(false);
+        };
+
+        Some((i + HASHSIZE, changes))
+    }
+}
+
+pub struct Inner {
+    pub a: u64,
+    pub b: u64,
+    pub c: u64,
+    pub d: u64,
+}
+
+impl CachedTreeHash for Inner {
+    fn cached_hash_tree_root(
+        &self,
+        other: &Self,
+        cache: &mut [u8],
+        i: usize,
+        mut changes: Vec<bool>,
+    ) -> Option<(usize, Vec<bool>)> {
+        let original_start = i;
+
+        let leaves = 4;
+        let nodes = num_nodes(leaves);
+        let internal = nodes - leaves;
+        let leaves_start = i + internal * HASHSIZE;
+
+        let mut leaf_changes = {
+            let leaf_changes = Vec::with_capacity(leaves);
+            let leaf_start = leaves_start;
+
+            let (leaf_start, leaf_changes) =
+                self.a
+                    .cached_hash_tree_root(&other.a, cache, leaf_start, leaf_changes)?;
+            let (leaf_start, leaf_changes) =
+                self.b
+                    .cached_hash_tree_root(&other.b, cache, leaf_start, leaf_changes)?;
+            let (leaf_start, leaf_changes) =
+                self.c
+                    .cached_hash_tree_root(&other.c, cache, leaf_start, leaf_changes)?;
+            let (_leaf_start, leaf_changes) =
+                self.d
+                    .cached_hash_tree_root(&other.d, cache, leaf_start, leaf_changes)?;
+
+            leaf_changes
+        };
+
+        let any_changes = leaf_changes.iter().any(|&c| c);
+
+        changes.resize(changes.len() + internal, false);
+        changes.append(&mut leaf_changes);
+
+        if any_changes {
+            let mut i = internal;
+
+            while i > 0 {
+                let children = children(i);
+
+                if changes[children.0] | changes[children.1] {
+                    changes[parent(i)] = true;
+
+                    let children_start = children.0 * HASHSIZE;
+                    let children_end = children_start + 2 * HASHSIZE;
+                    let hash = hash(&cache.get(children_start..children_end)?);
+
+                    cache
+                        .get_mut(i * HASHSIZE..(i + 1) * HASHSIZE)?
+                        .copy_from_slice(&hash);
+                }
+                i += 1
+            }
+        }
+
+        Some((42, vec![any_changes]))
+    }
+}
+
+/// Get merkle root of some hashed values - the input leaf nodes is expected to already be hashed
+/// Outputs a `Vec<u8>` byte array of the merkle root given a set of leaf node values.
+pub fn cache_builder(values: &[u8]) -> Option<Vec<u8>> {
+    let leaves = values.len() / HASHSIZE;
+
+    if leaves == 0 || !leaves.is_power_of_two() {
+        return None;
+    }
+
+    let mut o: Vec<u8> = vec![0; (num_nodes(leaves) - leaves) * HASHSIZE];
+    o.append(&mut values.to_vec());
+
+    let mut i = o.len();
+    let mut j = o.len() - values.len();
+
+    while i >= MERKLE_HASH_CHUNCK {
+        i -= MERKLE_HASH_CHUNCK;
+        let hash = hash(&o[i..i + MERKLE_HASH_CHUNCK]);
+
+        j -= HASHSIZE;
+        o.get_mut(j..j + HASHSIZE)?.copy_from_slice(&hash);
+    }
+
+    return Some(o);
+}
+
+fn parent(child: usize) -> usize {
+    (child - 1) / 2
+}
+
+fn children(parent: usize) -> (usize, usize) {
+    ((2 * parent + 1), (2 * parent + 2))
+}
+
+fn num_nodes(num_leaves: usize) -> usize {
+    2 * num_leaves - 1
+}
+
+pub struct Outer {
+    pub a: u64,
+    pub b: u64,
+    pub inner: Inner,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn join(many: Vec<&[u8]>) -> Vec<u8> {
+        let mut all = vec![];
+        for one in many {
+            all.extend_from_slice(&mut one.clone())
+        }
+        all
+    }
+
+    /*
+    #[test]
+    fn container() {
+        let data1 = hash(&vec![1; 32]);
+        let data2 = hash(&vec![2; 32]);
+        let data3 = hash(&vec![3; 32]);
+        let data4 = hash(&vec![4; 32]);
+
+        let data = join(vec![&data1, &data2, &data3, &data4]);
+
+        let cache = cache_builder(&data).unwrap();
+    }
+    */
+
+    #[test]
+    fn can_build_cache() {
+        let data1 = hash(&vec![1; 32]);
+        let data2 = hash(&vec![2; 32]);
+        let data3 = hash(&vec![3; 32]);
+        let data4 = hash(&vec![4; 32]);
+
+        let data = join(vec![&data1, &data2, &data3, &data4]);
+
+        let cache = cache_builder(&data).unwrap();
+
+        let hash_12 = {
+            let mut joined = vec![];
+            joined.append(&mut data1.clone());
+            joined.append(&mut data2.clone());
+            hash(&joined)
+        };
+        let hash_34 = {
+            let mut joined = vec![];
+            joined.append(&mut data3.clone());
+            joined.append(&mut data4.clone());
+            hash(&joined)
+        };
+        let hash_hash12_hash_34 = {
+            let mut joined = vec![];
+            joined.append(&mut hash_12.clone());
+            joined.append(&mut hash_34.clone());
+            hash(&joined)
+        };
+
+        for (i, chunk) in cache.chunks(HASHSIZE).enumerate().rev() {
+            let expected = match i {
+                0 => hash_hash12_hash_34.clone(),
+                1 => hash_12.clone(),
+                2 => hash_34.clone(),
+                3 => data1.clone(),
+                4 => data2.clone(),
+                5 => data3.clone(),
+                6 => data4.clone(),
+                _ => vec![],
+            };
+
+            assert_eq!(chunk, &expected[..], "failed at {}", i);
+        }
+    }
+}
+
+/*
+pub trait TreeHash {
+    fn hash_tree_root(&self) -> Vec<u8>;
+}
+
+/// Returns a 32 byte hash of 'list' - a vector of byte vectors.
+/// Note that this will consume 'list'.
+pub fn merkle_hash(list: &mut Vec<Vec<u8>>) -> Vec<u8> {
+    // flatten list
+    let mut chunkz = list_to_blob(list);
+
+    // get data_len as bytes. It will hashed will the merkle root
+    let mut datalen = list.len().to_le_bytes().to_vec();
+    zpad(&mut datalen, 32);
+
+    // merklelize
+    while chunkz.len() > HASHSIZE {
+        let mut new_chunkz: Vec<u8> = Vec::new();
+
+        for two_chunks in chunkz.chunks(BYTES_PER_CHUNK * 2) {
+            // Hash two chuncks together
+            new_chunkz.append(&mut hash(two_chunks));
+        }
+
+        chunkz = new_chunkz;
+    }
+
+    chunkz.append(&mut datalen);
+    hash(&chunkz)
+}
+
+fn list_to_blob(list: &mut Vec<Vec<u8>>) -> Vec<u8> {
+    // pack - fit as many many items per chunk as we can and then
+    // right pad to BYTES_PER_CHUNCK
+    let (items_per_chunk, chunk_count) = if list.is_empty() {
+        (1, 1)
+    } else {
+        let items_per_chunk = BYTES_PER_CHUNK / list[0].len();
+        let chunk_count = list.len() / items_per_chunk;
+        (items_per_chunk, chunk_count)
+    };
+
+    let mut chunkz = Vec::new();
+    if list.is_empty() {
+        // handle and empty list
+        chunkz.append(&mut vec![0; BYTES_PER_CHUNK * 2]);
+    } else if list[0].len() <= BYTES_PER_CHUNK {
+        // just create a blob here; we'll divide into
+        // chunked slices when we merklize
+        let mut chunk = Vec::with_capacity(BYTES_PER_CHUNK);
+        let mut item_count_in_chunk = 0;
+        chunkz.reserve(chunk_count * BYTES_PER_CHUNK);
+        for item in list.iter_mut() {
+            item_count_in_chunk += 1;
+            chunk.append(item);
+
+            // completed chunk?
+            if item_count_in_chunk == items_per_chunk {
+                zpad(&mut chunk, BYTES_PER_CHUNK);
+                chunkz.append(&mut chunk);
+                item_count_in_chunk = 0;
+            }
+        }
+
+        // left-over uncompleted chunk?
+        if item_count_in_chunk != 0 {
+            zpad(&mut chunk, BYTES_PER_CHUNK);
+            chunkz.append(&mut chunk);
+        }
+    }
+
+    // extend the number of chunks to a power of two if necessary
+    if !chunk_count.is_power_of_two() {
+        let zero_chunks_count = chunk_count.next_power_of_two() - chunk_count;
+        chunkz.append(&mut vec![0; zero_chunks_count * BYTES_PER_CHUNK]);
+    }
+
+    chunkz
+}
+
+/// right pads with zeros making 'bytes' 'size' in length
+fn zpad(bytes: &mut Vec<u8>, size: usize) {
+    if bytes.len() < size {
+        bytes.resize(size, 0);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_merkle_hash() {
+        let data1 = vec![1; 32];
+        let data2 = vec![2; 32];
+        let data3 = vec![3; 32];
+        let mut list = vec![data1, data2, data3];
+        let result = merkle_hash(&mut list);
+
+        //note: should test againt a known test hash value
+        assert_eq!(HASHSIZE, result.len());
+    }
+}
+*/
diff --git a/eth2/utils/ssz/src/lib.rs b/eth2/utils/ssz/src/lib.rs
index 7c29667af..9bf441249 100644
--- a/eth2/utils/ssz/src/lib.rs
+++ b/eth2/utils/ssz/src/lib.rs
@@ -10,6 +10,7 @@
 extern crate bytes;
 extern crate ethereum_types;
 
+mod cached_tree_hash;
 pub mod decode;
 pub mod encode;
 mod signed_root;