diff --git a/.gitignore b/.gitignore
index 346ef9afa..ad0c3c152 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,3 +4,4 @@ Cargo.lock
 *.pk
 *.sk
 *.raw_keypairs
+eth2/state_processing/yaml_utils/specs/*.yaml
diff --git a/Cargo.toml b/Cargo.toml
index cb070cc2d..94b2af017 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -4,6 +4,7 @@ members = [
 	"eth2/block_proposer",
 	"eth2/fork_choice",
 	"eth2/state_processing",
+	"eth2/state_processing/yaml_utils",
 	"eth2/types",
 	"eth2/utils/bls",
 	"eth2/utils/boolean-bitfield",
diff --git a/eth2/state_processing/Cargo.toml b/eth2/state_processing/Cargo.toml
index 4e37fce0c..62722aac8 100644
--- a/eth2/state_processing/Cargo.toml
+++ b/eth2/state_processing/Cargo.toml
@@ -14,6 +14,7 @@ env_logger = "0.6.0"
 serde = "1.0"
 serde_derive = "1.0"
 serde_yaml = "0.8"
+yaml-utils = { path = "yaml_utils" }
 
 [dependencies]
 bls = { path = "../utils/bls" }
diff --git a/eth2/state_processing/specs/example.yml b/eth2/state_processing/specs/example.yml
deleted file mode 100644
index 982f0b0dd..000000000
--- a/eth2/state_processing/specs/example.yml
+++ /dev/null
@@ -1,708 +0,0 @@
-title: Sanity tests -- small config -- 32 validators
-summary: Basic sanity checks from phase 0 spec pythonization using a small state configuration and 32 validators.
-    All tests are run with `verify_signatures` as set to False.
-    Tests generated via https://github.com/ethereum/research/blob/master/spec_pythonizer/sanity_check.py
-test_suite: beacon_state
-fork: phase0-0.5.0
-test_cases:
-- name: test_empty_block_transition
-  config:
-    SHARD_COUNT: 8
-    TARGET_COMMITTEE_SIZE: 4
-    MAX_BALANCE_CHURN_QUOTIENT: 32
-    MAX_INDICES_PER_SLASHABLE_VOTE: 4096
-    MAX_EXIT_DEQUEUES_PER_EPOCH: 4
-    SHUFFLE_ROUND_COUNT: 90
-    DEPOSIT_CONTRACT_TREE_DEPTH: 32
-    MIN_DEPOSIT_AMOUNT: 1000000000
-    MAX_DEPOSIT_AMOUNT: 32000000000
-    FORK_CHOICE_BALANCE_INCREMENT: 1000000000
-    EJECTION_BALANCE: 16000000000
-    GENESIS_FORK_VERSION: 0
-    GENESIS_SLOT: 4294967296
-    GENESIS_EPOCH: 536870912
-    GENESIS_START_SHARD: 0
-    BLS_WITHDRAWAL_PREFIX_BYTE: '0x00'
-    SECONDS_PER_SLOT: 6
-    MIN_ATTESTATION_INCLUSION_DELAY: 2
-    SLOTS_PER_EPOCH: 8
-    MIN_SEED_LOOKAHEAD: 1
-    ACTIVATION_EXIT_DELAY: 4
-    EPOCHS_PER_ETH1_VOTING_PERIOD: 16
-    SLOTS_PER_HISTORICAL_ROOT: 64
-    MIN_VALIDATOR_WITHDRAWABILITY_DELAY: 256
-    PERSISTENT_COMMITTEE_PERIOD: 2048
-    LATEST_RANDAO_MIXES_LENGTH: 64
-    LATEST_ACTIVE_INDEX_ROOTS_LENGTH: 64
-    LATEST_SLASHED_EXIT_LENGTH: 64
-    BASE_REWARD_QUOTIENT: 32
-    WHISTLEBLOWER_REWARD_QUOTIENT: 512
-    ATTESTATION_INCLUSION_REWARD_QUOTIENT: 8
-    INACTIVITY_PENALTY_QUOTIENT: 16777216
-    MIN_PENALTY_QUOTIENT: 32
-    MAX_PROPOSER_SLASHINGS: 16
-    MAX_ATTESTER_SLASHINGS: 1
-    MAX_ATTESTATIONS: 128
-    MAX_DEPOSITS: 16
-    MAX_VOLUNTARY_EXITS: 16
-    MAX_TRANSFERS: 16
-    DOMAIN_BEACON_BLOCK: 0
-    DOMAIN_RANDAO: 1
-    DOMAIN_ATTESTATION: 2
-    DOMAIN_DEPOSIT: 3
-    DOMAIN_VOLUNTARY_EXIT: 4
-    DOMAIN_TRANSFER: 5
-  verify_signatures: false
-  initial_state:
-    slot: 4294967296
-    genesis_time: 0
-    fork:
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-      current_version: '0x00000000'
-      epoch: 536870912
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diff --git a/eth2/state_processing/tests/tests.rs b/eth2/state_processing/tests/tests.rs
index b6aa3e76f..39882cafb 100644
--- a/eth2/state_processing/tests/tests.rs
+++ b/eth2/state_processing/tests/tests.rs
@@ -1,5 +1,7 @@
 use serde_derive::Deserialize;
 use types::*;
+#[allow(unused_imports)]
+use yaml_utils;
 
 #[derive(Debug, Deserialize)]
 pub struct TestCase {
@@ -23,9 +25,10 @@ fn yaml() {
     use serde_yaml;
     use std::{fs::File, io::prelude::*, path::PathBuf};
 
+    // Test sanity-check_small-config_32-vals.yaml
     let mut file = {
         let mut file_path_buf = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
-        file_path_buf.push("specs/example.yml");
+        file_path_buf.push("yaml_utils/specs/sanity-check_small-config_32-vals.yaml");
 
         File::open(file_path_buf).unwrap()
     };
@@ -34,7 +37,23 @@ fn yaml() {
 
     file.read_to_string(&mut yaml_str).unwrap();
 
-    let yaml_str = yaml_str.to_lowercase();
+    yaml_str = yaml_str.to_lowercase();
+
+    let _doc: TestDoc = serde_yaml::from_str(&yaml_str.as_str()).unwrap();
+
+    // Test sanity-check_default-config_100-vals.yaml
+    file = {
+        let mut file_path_buf = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+        file_path_buf.push("yaml_utils/specs/sanity-check_default-config_100-vals.yaml");
+
+        File::open(file_path_buf).unwrap()
+    };
+
+    yaml_str = String::new();
+
+    file.read_to_string(&mut yaml_str).unwrap();
+
+    yaml_str = yaml_str.to_lowercase();
 
     let _doc: TestDoc = serde_yaml::from_str(&yaml_str.as_str()).unwrap();
 }
diff --git a/eth2/state_processing/yaml_utils/Cargo.toml b/eth2/state_processing/yaml_utils/Cargo.toml
new file mode 100644
index 000000000..4a7ae5b89
--- /dev/null
+++ b/eth2/state_processing/yaml_utils/Cargo.toml
@@ -0,0 +1,15 @@
+[package]
+name = "yaml-utils"
+version = "0.1.0"
+authors = ["Kirk Baird <baird.k@outlook.com>"]
+edition = "2018"
+
+[build-dependencies]
+reqwest = "0.9"
+tempdir = "0.3"
+
+[dependencies]
+
+[lib]
+name = "yaml_utils"
+path = "src/lib.rs"
diff --git a/eth2/state_processing/yaml_utils/build.rs b/eth2/state_processing/yaml_utils/build.rs
new file mode 100644
index 000000000..3b7f31471
--- /dev/null
+++ b/eth2/state_processing/yaml_utils/build.rs
@@ -0,0 +1,28 @@
+extern crate reqwest;
+extern crate tempdir;
+
+use std::fs::File;
+use std::io::copy;
+
+fn main() {
+    // These test files are not to be stored in the lighthouse repo as they are quite large (32MB).
+    // They will be downloaded at build time by yaml-utils crate (in build.rs)
+    let git_path = "https://raw.githubusercontent.com/ethereum/eth2.0-tests/master/state/";
+    let test_names = vec![
+        "sanity-check_default-config_100-vals.yaml",
+        "sanity-check_small-config_32-vals.yaml",
+    ];
+
+    for test in test_names {
+        let mut target = String::from(git_path);
+        target.push_str(test);
+        let mut response = reqwest::get(target.as_str()).unwrap();
+
+        let mut dest = {
+            let mut file_name = String::from("specs/");
+            file_name.push_str(test);
+            File::create(file_name).unwrap()
+        };
+        copy(&mut response, &mut dest).unwrap();
+    }
+}
diff --git a/eth2/state_processing/yaml_utils/src/lib.rs b/eth2/state_processing/yaml_utils/src/lib.rs
new file mode 100644
index 000000000..644ea434b
--- /dev/null
+++ b/eth2/state_processing/yaml_utils/src/lib.rs
@@ -0,0 +1 @@
+// This is a place holder such that yaml-utils is now a crate hence build.rs will be run when 'cargo test' is called
diff --git a/eth2/types/src/test_utils/serde_utils.rs b/eth2/types/src/test_utils/serde_utils.rs
index e0e88fbec..761aee523 100644
--- a/eth2/types/src/test_utils/serde_utils.rs
+++ b/eth2/types/src/test_utils/serde_utils.rs
@@ -1,6 +1,8 @@
 use serde::de::Error;
 use serde::{Deserialize, Deserializer};
 
+pub const FORK_BYTES_LEN: usize = 4;
+
 pub fn u8_from_hex_str<'de, D>(deserializer: D) -> Result<u8, D::Error>
 where
     D: Deserializer<'de>,
@@ -10,14 +12,18 @@ where
     u8::from_str_radix(&s.as_str()[2..], 16).map_err(D::Error::custom)
 }
 
-pub fn fork_from_hex_str<'de, D>(deserializer: D) -> Result<[u8; 4], D::Error>
+pub fn fork_from_hex_str<'de, D>(deserializer: D) -> Result<[u8; FORK_BYTES_LEN], D::Error>
 where
     D: Deserializer<'de>,
 {
     let s: String = Deserialize::deserialize(deserializer)?;
-    let mut array = [0 as u8; 4];
+    let mut array = [0 as u8; FORK_BYTES_LEN];
     let decoded: Vec<u8> = hex::decode(&s.as_str()[2..]).map_err(D::Error::custom)?;
 
+    if decoded.len() > FORK_BYTES_LEN {
+        return Err(D::Error::custom("Fork length too long"));
+    }
+
     for (i, item) in array.iter_mut().enumerate() {
         if i > decoded.len() {
             break;
diff --git a/eth2/utils/bls/src/aggregate_signature.rs b/eth2/utils/bls/src/aggregate_signature.rs
index 7b80d3bbf..922fae4f6 100644
--- a/eth2/utils/bls/src/aggregate_signature.rs
+++ b/eth2/utils/bls/src/aggregate_signature.rs
@@ -1,30 +1,39 @@
-use super::{AggregatePublicKey, Signature};
+use super::{AggregatePublicKey, Signature, BLS_AGG_SIG_BYTE_SIZE};
 use bls_aggregates::{
     AggregatePublicKey as RawAggregatePublicKey, AggregateSignature as RawAggregateSignature,
 };
 use serde::de::{Deserialize, Deserializer};
 use serde::ser::{Serialize, Serializer};
 use serde_hex::{encode as hex_encode, PrefixedHexVisitor};
-use ssz::{
-    decode_ssz_list, hash, ssz_encode, Decodable, DecodeError, Encodable, SszStream, TreeHash,
-};
+use ssz::{decode_ssz_list, hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 
 /// A BLS aggregate signature.
 ///
 /// This struct is a wrapper upon a base type and provides helper functions (e.g., SSZ
 /// serialization).
 #[derive(Debug, PartialEq, Clone, Default, Eq)]
-pub struct AggregateSignature(RawAggregateSignature);
+pub struct AggregateSignature {
+    aggregate_signature: RawAggregateSignature,
+    is_empty: bool,
+}
 
 impl AggregateSignature {
     /// Instantiate a new AggregateSignature.
+    ///
+    /// is_empty is false
+    /// AggregateSiganture is point at infinity
     pub fn new() -> Self {
-        AggregateSignature(RawAggregateSignature::new())
+        Self {
+            aggregate_signature: RawAggregateSignature::new(),
+            is_empty: false,
+        }
     }
 
     /// Add (aggregate) a signature to the `AggregateSignature`.
     pub fn add(&mut self, signature: &Signature) {
-        self.0.add(signature.as_raw())
+        if !self.is_empty {
+            self.aggregate_signature.add(signature.as_raw())
+        }
     }
 
     /// Verify the `AggregateSignature` against an `AggregatePublicKey`.
@@ -37,7 +46,11 @@ impl AggregateSignature {
         domain: u64,
         aggregate_public_key: &AggregatePublicKey,
     ) -> bool {
-        self.0.verify(msg, domain, aggregate_public_key.as_raw())
+        if self.is_empty {
+            return false;
+        }
+        self.aggregate_signature
+            .verify(msg, domain, aggregate_public_key.as_raw())
     }
 
     /// Verify this AggregateSignature against multiple AggregatePublickeys with multiple Messages.
@@ -50,6 +63,9 @@ impl AggregateSignature {
         domain: u64,
         aggregate_public_keys: &[&AggregatePublicKey],
     ) -> bool {
+        if self.is_empty {
+            return false;
+        }
         let aggregate_public_keys: Vec<&RawAggregatePublicKey> =
             aggregate_public_keys.iter().map(|pk| pk.as_raw()).collect();
 
@@ -59,14 +75,53 @@ impl AggregateSignature {
             msg.extend_from_slice(message);
         }
 
-        self.0
+        self.aggregate_signature
             .verify_multiple(&msg[..], domain, &aggregate_public_keys[..])
     }
+
+    /// Return AggregateSiganture as bytes
+    pub fn as_bytes(&self) -> Vec<u8> {
+        if self.is_empty {
+            return vec![0; BLS_AGG_SIG_BYTE_SIZE];
+        }
+        self.aggregate_signature.as_bytes()
+    }
+
+    /// Convert bytes to AggregateSiganture
+    pub fn from_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
+        for byte in bytes {
+            if *byte != 0 {
+                let sig =
+                    RawAggregateSignature::from_bytes(&bytes).map_err(|_| DecodeError::Invalid)?;
+                return Ok(Self {
+                    aggregate_signature: sig,
+                    is_empty: false,
+                });
+            }
+        }
+        Ok(Self::empty_signature())
+    }
+
+    /// Returns if the AggregateSiganture `is_empty`
+    pub fn is_empty(&self) -> bool {
+        self.is_empty
+    }
+
+    /// Creates a new AggregateSignature
+    ///
+    /// aggregate_signature set to the point infinity
+    /// is_empty set to true
+    pub fn empty_signature() -> Self {
+        Self {
+            aggregate_signature: RawAggregateSignature::new(),
+            is_empty: true,
+        }
+    }
 }
 
 impl Encodable for AggregateSignature {
     fn ssz_append(&self, s: &mut SszStream) {
-        s.append_vec(&self.0.as_bytes());
+        s.append_vec(&self.as_bytes());
     }
 }
 
@@ -74,35 +129,43 @@ impl Decodable for AggregateSignature {
     fn ssz_decode(bytes: &[u8], i: usize) -> Result<(Self, usize), DecodeError> {
         let (sig_bytes, i) = decode_ssz_list(bytes, i)?;
         let raw_sig =
-            RawAggregateSignature::from_bytes(&sig_bytes).map_err(|_| DecodeError::TooShort)?;
-        Ok((AggregateSignature(raw_sig), i))
+            RawAggregateSignature::from_bytes(&sig_bytes).map_err(|_| DecodeError::Invalid)?;
+        Ok((
+            Self {
+                aggregate_signature: raw_sig,
+                is_empty: false,
+            },
+            i,
+        ))
     }
 }
 
 impl Serialize for AggregateSignature {
+    /// Serde serialization is compliant the Ethereum YAML test format.
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
         S: Serializer,
     {
-        serializer.serialize_str(&hex_encode(ssz_encode(self)))
+        serializer.serialize_str(&hex_encode(self.as_bytes()))
     }
 }
 
 impl<'de> Deserialize<'de> for AggregateSignature {
+    /// Serde serialization is compliant the Ethereum YAML test format.
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
         D: Deserializer<'de>,
     {
         let bytes = deserializer.deserialize_str(PrefixedHexVisitor)?;
-        let (obj, _) = <_>::ssz_decode(&bytes[..], 0)
+        let agg_sig = AggregateSignature::from_bytes(&bytes[..])
             .map_err(|e| serde::de::Error::custom(format!("invalid ssz ({:?})", e)))?;
-        Ok(obj)
+        Ok(agg_sig)
     }
 }
 
 impl TreeHash for AggregateSignature {
     fn hash_tree_root(&self) -> Vec<u8> {
-        hash(&self.0.as_bytes())
+        hash(&self.as_bytes())
     }
 }
 
diff --git a/eth2/utils/bls/src/lib.rs b/eth2/utils/bls/src/lib.rs
index 38a129908..77fd531f7 100644
--- a/eth2/utils/bls/src/lib.rs
+++ b/eth2/utils/bls/src/lib.rs
@@ -17,6 +17,7 @@ pub use crate::secret_key::SecretKey;
 pub use crate::signature::Signature;
 
 pub const BLS_AGG_SIG_BYTE_SIZE: usize = 96;
+pub const BLS_SIG_BYTE_SIZE: usize = 96;
 
 use hashing::hash;
 use ssz::ssz_encode;
diff --git a/eth2/utils/bls/src/signature.rs b/eth2/utils/bls/src/signature.rs
index 8a080e56d..42c307cbe 100644
--- a/eth2/utils/bls/src/signature.rs
+++ b/eth2/utils/bls/src/signature.rs
@@ -1,5 +1,5 @@
 use super::serde_vistors::HexVisitor;
-use super::{PublicKey, SecretKey};
+use super::{PublicKey, SecretKey, BLS_SIG_BYTE_SIZE};
 use bls_aggregates::Signature as RawSignature;
 use hex::encode as hex_encode;
 use serde::de::{Deserialize, Deserializer};
@@ -63,7 +63,7 @@ impl Signature {
     /// Returns a new empty signature.
     pub fn empty_signature() -> Self {
         // Set RawSignature = infinity
-        let mut empty: Vec<u8> = vec![0; 96];
+        let mut empty: Vec<u8> = vec![0; BLS_SIG_BYTE_SIZE];
         empty[0] += u8::pow(2, 6) + u8::pow(2, 7);
         Signature {
             signature: RawSignature::from_bytes(&empty).unwrap(),
@@ -121,6 +121,7 @@ impl TreeHash for Signature {
 }
 
 impl Serialize for Signature {
+    /// Serde serialization is compliant the Ethereum YAML test format.
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
         S: Serializer,
@@ -130,14 +131,15 @@ impl Serialize for Signature {
 }
 
 impl<'de> Deserialize<'de> for Signature {
+    /// Serde serialization is compliant the Ethereum YAML test format.
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
         D: Deserializer<'de>,
     {
-        let bytes = deserializer.deserialize_str(HexVisitor)?;
-        let (pubkey, _) = <_>::ssz_decode(&bytes[..], 0)
+        let bytes: Vec<u8> = deserializer.deserialize_str(HexVisitor)?;
+        let signature = Signature::from_bytes(&bytes[..])
             .map_err(|e| serde::de::Error::custom(format!("invalid ssz ({:?})", e)))?;
-        Ok(pubkey)
+        Ok(signature)
     }
 }
 
@@ -165,7 +167,7 @@ mod tests {
 
         let sig_as_bytes: Vec<u8> = sig.as_raw().as_bytes();
 
-        assert_eq!(sig_as_bytes.len(), 96);
+        assert_eq!(sig_as_bytes.len(), BLS_SIG_BYTE_SIZE);
         for (i, one_byte) in sig_as_bytes.iter().enumerate() {
             if i == 0 {
                 assert_eq!(*one_byte, u8::pow(2, 6) + u8::pow(2, 7));
diff --git a/eth2/utils/boolean-bitfield/src/lib.rs b/eth2/utils/boolean-bitfield/src/lib.rs
index 443cd06da..161b365bb 100644
--- a/eth2/utils/boolean-bitfield/src/lib.rs
+++ b/eth2/utils/boolean-bitfield/src/lib.rs
@@ -186,7 +186,7 @@ impl Serialize for BooleanBitfield {
     where
         S: Serializer,
     {
-        serializer.serialize_str(&encode(&ssz::ssz_encode(self)))
+        serializer.serialize_str(&encode(&self.to_bytes()))
     }
 }
 
@@ -197,9 +197,7 @@ impl<'de> Deserialize<'de> for BooleanBitfield {
         D: Deserializer<'de>,
     {
         let bytes = deserializer.deserialize_str(PrefixedHexVisitor)?;
-        let (bitfield, _) = <_>::ssz_decode(&bytes[..], 0)
-            .map_err(|e| serde::de::Error::custom(format!("invalid ssz ({:?})", e)))?;
-        Ok(bitfield)
+        Ok(BooleanBitfield::from_bytes(&bytes))
     }
 }