diff --git a/cumulus/Cargo.lock b/cumulus/Cargo.lock
index 95e39bad8f..5054b73f82 100644
--- a/cumulus/Cargo.lock
+++ b/cumulus/Cargo.lock
@@ -1193,9 +1193,11 @@ dependencies = [
  "sp-blockchain",
  "sp-consensus",
  "sp-core",
+ "sp-externalities",
  "sp-io",
  "sp-keyring",
  "sp-runtime",
+ "sp-state-machine",
  "sp-std",
  "sp-trie",
  "trie-db",
diff --git a/cumulus/runtime/Cargo.toml b/cumulus/runtime/Cargo.toml
index 19a4dace6c..b781567896 100644
--- a/cumulus/runtime/Cargo.toml
+++ b/cumulus/runtime/Cargo.toml
@@ -21,6 +21,8 @@ sp-core = { git = "https://github.com/paritytech/substrate", default-features =
 sp-io = { git = "https://github.com/paritytech/substrate", default-features = false, branch = "master" }
 frame-executive = { git = "https://github.com/paritytech/substrate", default-features = false, branch = "master" }
 sp-trie = { git = "https://github.com/paritytech/substrate", default-features = false, branch = "master" }
+sp-state-machine = { git = "https://github.com/paritytech/substrate", default-features = false, branch = "master" }
+sp-externalities = { git = "https://github.com/paritytech/substrate", default-features = false, branch = "master" }
 
 # Polkadot dependencies
 parachain = { package = "polkadot-parachain", git = "https://github.com/paritytech/polkadot", default-features = false, features = [ "wasm-api" ] , branch = "master" }
@@ -48,6 +50,8 @@ std = [
 	"memory-db/std",
 	"hash-db/std",
 	"trie-db/std",
+	"sp-state-machine/std",
+	"sp-externalities/std",
 	"sp-trie/std",
 	"parachain/std",
 ]
diff --git a/cumulus/runtime/src/validate_block/implementation.rs b/cumulus/runtime/src/validate_block/implementation.rs
index abcbea5ffd..51bc9c3619 100644
--- a/cumulus/runtime/src/validate_block/implementation.rs
+++ b/cumulus/runtime/src/validate_block/implementation.rs
@@ -17,18 +17,15 @@
 //! The actual implementation of the validate block functionality.
 
 use frame_executive::ExecuteBlock;
-use sp_runtime::traits::{Block as BlockT, HashFor, Header as HeaderT};
+use sp_runtime::traits::{Block as BlockT, HashFor, NumberFor, Header as HeaderT};
 
-use sp_std::{boxed::Box, collections::btree_map::BTreeMap, ops::Bound, vec::Vec};
-use sp_trie::{delta_trie_root, read_trie_value, Layout, MemoryDB, StorageProof};
+use sp_std::{boxed::Box, vec::Vec};
 
 use hash_db::{HashDB, EMPTY_PREFIX};
 
-use trie_db::{Trie, TrieDB, TrieDBIterator};
-
 use parachain::primitives::{HeadData, ValidationCode, ValidationParams, ValidationResult};
 
-use codec::{Decode, Encode, EncodeAppend};
+use codec::{Decode, Encode};
 
 use cumulus_primitives::{
 	well_known_keys::{
@@ -36,60 +33,25 @@ use cumulus_primitives::{
 	},
 	GenericUpwardMessage, ValidationData,
 };
+use sp_externalities::{set_and_run_with_externalities};
+use sp_externalities::{Externalities, ExtensionStore, Error, Extension};
+use sp_trie::MemoryDB;
+use sp_std::{any::{TypeId, Any}};
+use sp_core::storage::{ChildInfo, TrackedStorageKey};
 
-/// Stores the global [`Storage`] instance.
-///
-/// As wasm is always executed with one thread, this global varibale is safe!
-static mut STORAGE: Option<Box<dyn Storage>> = None;
+type StorageValue = Vec<u8>;
+type StorageKey = Vec<u8>;
 
-/// Runs the given `call` with the global storage and returns the result of the call.
-///
-/// # Panic
-///
-/// Panics if the [`STORAGE`] is not initialized.
-fn with_storage<R>(call: impl FnOnce(&mut dyn Storage) -> R) -> R {
-	let mut storage = unsafe {
-		STORAGE
-			.take()
-			.expect("`STORAGE` needs to be set before calling this function.")
-	};
+type Ext<'a, B: BlockT> = sp_state_machine::Ext<
+	'a,
+	HashFor<B>,
+	NumberFor<B>,
+	sp_state_machine::TrieBackend<MemoryDB<HashFor<B>>, HashFor<B>>,
+>;
 
-	let res = call(&mut *storage);
-
-	unsafe {
-		STORAGE = Some(storage);
-	}
-
-	res
-}
-
-/// Abstract the storage into a trait without `Block` generic.
-trait Storage {
-	/// Retrieve the value for the given key.
-	fn get(&self, key: &[u8]) -> Option<Vec<u8>>;
-
-	/// Retrieve the value for the given key only if modified.
-	fn modified(&self, key: &[u8]) -> Option<Vec<u8>>;
-
-	/// Insert the given key and value.
-	fn insert(&mut self, key: &[u8], value: &[u8]);
-
-	/// Remove key and value.
-	fn remove(&mut self, key: &[u8]);
-
-	/// Calculate the storage root.
-	///
-	/// Returns the SCALE encoded hash.
-	fn storage_root(&mut self) -> Vec<u8>;
-
-	/// Clear all keys that start with the given prefix.
-	fn clear_prefix(&mut self, prefix: &[u8]);
-
-	/// Append the value to the given key
-	fn storage_append(&mut self, key: &[u8], value: Vec<u8>);
-
-	/// Get the next storage key after the given `key`.
-	fn next_key(&self, key: &[u8]) -> Option<Vec<u8>>;
+fn with_externalities<F: FnOnce(&mut dyn Externalities) -> R, R>(f: F) -> R {
+	sp_externalities::with_externalities(f)
+		.expect("Environmental externalities not set.")
 }
 
 /// Implement `Encode` by forwarding the stored raw vec.
@@ -118,15 +80,23 @@ pub fn validate_block<B: BlockT, E: ExecuteBlock<B>>(params: ValidationParams) -
 		"Invalid parent hash",
 	);
 
-	let storage_inner = WitnessStorage::<B>::new(
-		block_data.storage_proof,
-		parent_head.state_root().clone(),
-		params,
-	)
-	.expect("Witness data and storage root always match; qed");
+	let db = block_data.storage_proof.into_memory_db();
+	let root = parent_head.state_root().clone();
+	if !HashDB::<HashFor<B>, _>::contains(&db, &root, EMPTY_PREFIX) {
+		panic!("Witness data does not contain given storage root.");
+	}
+	let backend = sp_state_machine::TrieBackend::new(
+		db,
+		root,
+	);
+	let mut overlay = sp_state_machine::OverlayedChanges::default();
+	let mut cache = Default::default();
+	let mut ext = WitnessExt::<B> {
+		inner: Ext::<B>::new(&mut overlay, &mut cache, &backend),
+		params: &params,
+	};
 
 	let _guard = unsafe {
-		STORAGE = Some(Box::new(storage_inner));
 		(
 			// Replace storage calls with our own implementations
 			sp_io::storage::host_read.replace_implementation(host_storage_read),
@@ -139,30 +109,56 @@ pub fn validate_block<B: BlockT, E: ExecuteBlock<B>>(params: ValidationParams) -
 			sp_io::storage::host_changes_root.replace_implementation(host_storage_changes_root),
 			sp_io::storage::host_append.replace_implementation(host_storage_append),
 			sp_io::storage::host_next_key.replace_implementation(host_storage_next_key),
+			sp_io::storage::host_start_transaction.replace_implementation(host_storage_start_transaction),
+			sp_io::storage::host_rollback_transaction.replace_implementation(
+				host_storage_rollback_transaction
+			),
+			sp_io::storage::host_commit_transaction.replace_implementation(
+				host_storage_commit_transaction
+			),
+			sp_io::default_child_storage::host_get.replace_implementation(host_default_child_storage_get),
+			sp_io::default_child_storage::host_read.replace_implementation(host_default_child_storage_read),
+			sp_io::default_child_storage::host_set.replace_implementation(host_default_child_storage_set),
+			sp_io::default_child_storage::host_clear.replace_implementation(
+				host_default_child_storage_clear
+			),
+			sp_io::default_child_storage::host_storage_kill.replace_implementation(
+				host_default_child_storage_storage_kill
+			),
+			sp_io::default_child_storage::host_exists.replace_implementation(
+				host_default_child_storage_exists
+			),
+			sp_io::default_child_storage::host_clear_prefix.replace_implementation(
+				host_default_child_storage_clear_prefix
+			),
+			sp_io::default_child_storage::host_root.replace_implementation(host_default_child_storage_root),
+			sp_io::default_child_storage::host_next_key.replace_implementation(host_default_child_storage_next_key),
 		)
 	};
 
-	E::execute_block(block);
+	set_and_run_with_externalities(&mut ext, || {
+		E::execute_block(block);
+	});
 
 	// If in the course of block execution new validation code was set, insert
 	// its scheduled upgrade so we can validate that block number later.
-	let new_validation_code =
-		with_storage(|storage| storage.modified(NEW_VALIDATION_CODE)).map(ValidationCode);
+	let new_validation_code = overlay.storage(NEW_VALIDATION_CODE).flatten()
+		.map(|slice| slice.to_vec())
+		.map(ValidationCode);
 
 	// Extract potential upward messages from the storage.
-	let upward_messages = match with_storage(|storage| storage.modified(UPWARD_MESSAGES)) {
+	let upward_messages = match overlay.storage(UPWARD_MESSAGES).flatten() {
 		Some(encoded) => Vec::<GenericUpwardMessage>::decode(&mut &encoded[..])
 			.expect("Upward messages vec is not correctly encoded in the storage!"),
 		None => Vec::new(),
 	};
 
-	let processed_downward_messages =
-		with_storage(|storage| storage.modified(PROCESSED_DOWNWARD_MESSAGES))
-			.and_then(|v| Decode::decode(&mut &v[..]).ok())
-			.unwrap_or_default();
+	let processed_downward_messages = overlay.storage(PROCESSED_DOWNWARD_MESSAGES)
+		.flatten()
+		.and_then(|v| Decode::decode(&mut &v[..]).ok())
+		.unwrap_or_default();
 
-	let validation_data: ValidationData =
-		with_storage(|storage| storage.modified(VALIDATION_DATA))
+	let validation_data: ValidationData = overlay.storage(VALIDATION_DATA).flatten()
 			.and_then(|v| Decode::decode(&mut &v[..]).ok())
 			.expect("`ValidationData` is required to be placed into the storage!");
 
@@ -180,192 +176,212 @@ pub fn validate_block<B: BlockT, E: ExecuteBlock<B>>(params: ValidationParams) -
 
 /// The storage implementation used when validating a block that is using the
 /// witness data as source.
-struct WitnessStorage<B: BlockT> {
-	witness_data: MemoryDB<HashFor<B>>,
-	overlay: BTreeMap<Vec<u8>, Option<Vec<u8>>>,
-	storage_root: B::Hash,
-	validation_params: ValidationParams,
+struct WitnessExt<'a, B: BlockT> {
+	inner: Ext<'a, B>,
+	params: &'a ValidationParams,
 }
 
-impl<B: BlockT> WitnessStorage<B> {
-	/// Initialize from the given witness data and storage root.
-	///
-	/// Returns an error if given storage root was not found in the witness data.
-	fn new(
-		storage_proof: StorageProof,
-		storage_root: B::Hash,
-		validation_params: ValidationParams,
-	) -> Result<Self, &'static str> {
-		let db = storage_proof.into_memory_db();
-
-		if !HashDB::contains(&db, &storage_root, EMPTY_PREFIX) {
-			return Err("Witness data does not contain given storage root.");
-		}
-
-		Ok(Self {
-			witness_data: db,
-			overlay: Default::default(),
-			storage_root,
-			validation_params,
-		})
-	}
-
-	/// Find the next storage key after the given `key` in the trie.
-	fn trie_next_key(&self, key: &[u8]) -> Option<Vec<u8>> {
-		let trie = TrieDB::<Layout<HashFor<B>>>::new(&self.witness_data, &self.storage_root)
-			.expect("Creates next storage key `TrieDB`");
-		let mut iter = trie.iter().expect("Creates trie iterator");
-
-		// The key just after the one given in input, basically `key++0`.
-		// Note: We are sure this is the next key if:
-		// * size of key has no limit (i.e. we can always add 0 to the path),
-		// * and no keys can be inserted between `key` and `key++0` (this is ensured by sp-io).
-		let mut potential_next_key = Vec::with_capacity(key.len() + 1);
-		potential_next_key.extend_from_slice(key);
-		potential_next_key.push(0);
-
-		iter.seek(&potential_next_key).expect("Seek trie iterator");
-
-		let next_element = iter.next();
-
-		if let Some(next_element) = next_element {
-			let (next_key, _) = next_element.expect("Extracts next key");
-			Some(next_key)
-		} else {
-			None
-		}
-	}
-
-	/// Find the next storage key after the given `key` in the overlay.
-	fn overlay_next_key(&self, key: &[u8]) -> Option<(&[u8], Option<&[u8]>)> {
-		let range = (Bound::Excluded(key), Bound::Unbounded);
-		self.overlay
-			.range::<[u8], _>(range)
-			.next()
-			.map(|(k, v)| (&k[..], v.as_deref()))
-	}
-
+impl<'a, B: BlockT> WitnessExt<'a, B> {
 	/// Checks that the encoded `ValidationData` in `data` is correct.
 	///
 	/// Should be removed with: https://github.com/paritytech/cumulus/issues/217
+	/// When removed `WitnessExt` could also be removed.
 	fn check_validation_data(&self, mut data: &[u8]) {
 		let validation_data = ValidationData::decode(&mut data).expect("Invalid `ValidationData`");
 
 		assert_eq!(
-			self.validation_params.parent_head,
+			self.params.parent_head,
 			validation_data.persisted.parent_head
 		);
 		assert_eq!(
-			self.validation_params.relay_chain_height,
+			self.params.relay_chain_height,
 			validation_data.persisted.block_number
 		);
 		assert_eq!(
-			self.validation_params.hrmp_mqc_heads,
+			self.params.hrmp_mqc_heads,
 			validation_data.persisted.hrmp_mqc_heads
 		);
 	}
 }
 
-impl<B: BlockT> Storage for WitnessStorage<B> {
-	fn modified(&self, key: &[u8]) -> Option<Vec<u8>> {
-		self.overlay.get(key).cloned().unwrap_or(None)
+impl<'a, B: BlockT> Externalities for WitnessExt<'a, B> {
+	fn storage(&self, key: &[u8]) -> Option<StorageValue> {
+		self.inner.storage(key)
 	}
 
-	fn get(&self, key: &[u8]) -> Option<Vec<u8>> {
-		self.overlay.get(key).cloned().unwrap_or_else(|| {
-			read_trie_value::<Layout<HashFor<B>>, _>(&self.witness_data, &self.storage_root, key)
-				.expect("Reading key from trie.")
-		})
+	fn set_offchain_storage(&mut self, key: &[u8], value: Option<&[u8]>) {
+		self.inner.set_offchain_storage(key, value)
 	}
 
-	fn insert(&mut self, key: &[u8], value: &[u8]) {
-		if key == VALIDATION_DATA {
-			self.check_validation_data(value);
+	fn storage_hash(&self, key: &[u8]) -> Option<Vec<u8>> {
+		self.inner.storage_hash(key)
+	}
+
+	fn child_storage(
+		&self,
+		child_info: &ChildInfo,
+		key: &[u8],
+	) -> Option<StorageValue> {
+		self.inner.child_storage(child_info, key)
+	}
+
+	fn child_storage_hash(
+		&self,
+		child_info: &ChildInfo,
+		key: &[u8],
+	) -> Option<Vec<u8>> {
+		self.inner.child_storage_hash(child_info, key)
+	}
+
+	fn exists_storage(&self, key: &[u8]) -> bool {
+		self.inner.exists_storage(key)
+	}
+
+	fn exists_child_storage(
+		&self,
+		child_info: &ChildInfo,
+		key: &[u8],
+	) -> bool {
+		self.inner.exists_child_storage(child_info, key)
+	}
+
+	fn next_storage_key(&self, key: &[u8]) -> Option<StorageKey> {
+		self.inner.next_storage_key(key)
+	}
+
+	fn next_child_storage_key(
+		&self,
+		child_info: &ChildInfo,
+		key: &[u8],
+	) -> Option<StorageKey> {
+		self.inner.next_child_storage_key(child_info, key)
+	}
+
+	fn place_storage(&mut self, key: StorageKey, value: Option<StorageValue>) {
+		if let Some(value) = value.as_ref() {
+			if key == VALIDATION_DATA {
+				self.check_validation_data(value);
+			}
 		}
 
-		self.overlay.insert(key.to_vec(), Some(value.to_vec()));
+		self.inner.place_storage(key, value)
 	}
 
-	fn remove(&mut self, key: &[u8]) {
-		self.overlay.insert(key.to_vec(), None);
+	fn place_child_storage(
+		&mut self,
+		child_info: &ChildInfo,
+		key: StorageKey,
+		value: Option<StorageValue>,
+	) {
+		self.inner.place_child_storage(child_info, key, value)
 	}
 
-	fn storage_root(&mut self) -> Vec<u8> {
-		let root = delta_trie_root::<Layout<HashFor<B>>, _, _, _, _, _>(
-			&mut self.witness_data,
-			self.storage_root.clone(),
-			self.overlay
-				.iter()
-				.map(|(k, v)| (k.as_ref(), v.as_ref().map(|v| v.as_ref()))),
-		)
-		.expect("Calculates storage root");
-
-		root.encode()
+	fn kill_child_storage(
+		&mut self,
+		child_info: &ChildInfo,
+	) {
+		self.inner.kill_child_storage(child_info)
 	}
 
 	fn clear_prefix(&mut self, prefix: &[u8]) {
-		self.overlay.iter_mut().for_each(|(k, v)| {
-			if k.starts_with(prefix) {
-				*v = None;
-			}
-		});
-
-		let trie = match TrieDB::<Layout<HashFor<B>>>::new(&self.witness_data, &self.storage_root) {
-			Ok(r) => r,
-			Err(_) => panic!(),
-		};
-
-		for x in TrieDBIterator::new_prefixed(&trie, prefix).expect("Creates trie iterator") {
-			if let Ok((key, _)) = x {
-				self.overlay.insert(key, None);
-			}
-		}
+		self.inner.clear_prefix(prefix)
 	}
 
-	fn storage_append(&mut self, key: &[u8], value: Vec<u8>) {
-		let value_vec = sp_std::vec![EncodeOpaqueValue(value)];
-
-		let overlay = &mut self.overlay;
-		let witness_data = &self.witness_data;
-		let storage_root = &self.storage_root;
-
-		let current_value = overlay.entry(key.to_vec()).or_insert_with(|| {
-			read_trie_value::<Layout<HashFor<B>>, _>(witness_data, storage_root, key)
-				.ok()
-				.flatten()
-		});
-
-		let item = current_value.take().unwrap_or_default();
-		*current_value = Some(
-			match Vec::<EncodeOpaqueValue>::append_or_new(item, &value_vec) {
-				Ok(item) => item,
-				Err(_) => value_vec.encode(),
-			},
-		);
+	fn clear_child_prefix(
+		&mut self,
+		child_info: &ChildInfo,
+		prefix: &[u8],
+	) {
+		self.inner.clear_child_prefix(child_info, prefix)
 	}
 
-	fn next_key(&self, key: &[u8]) -> Option<Vec<u8>> {
-		let next_trie_key = self.trie_next_key(key);
-		let next_overlay_key = self.overlay_next_key(key);
+	fn storage_append(
+		&mut self,
+		key: Vec<u8>,
+		value: Vec<u8>,
+	) {
+		self.inner.storage_append(key, value)
+	}
 
-		match (next_trie_key, next_overlay_key) {
-			(Some(backend_key), Some(overlay_key)) if &backend_key[..] < overlay_key.0 => {
-				Some(backend_key)
-			}
-			(backend_key, None) => backend_key,
-			(_, Some(overlay_key)) => {
-				if overlay_key.1.is_some() {
-					Some(overlay_key.0.to_vec())
-				} else {
-					self.next_key(&overlay_key.0)
-				}
-			}
-		}
+	fn chain_id(&self) -> u64 {
+		42
+	}
+
+	fn storage_root(&mut self) -> Vec<u8> {
+		self.inner.storage_root()
+	}
+
+	fn child_storage_root(
+		&mut self,
+		child_info: &ChildInfo,
+	) -> Vec<u8> {
+		self.inner.child_storage_root(child_info)
+	}
+
+	fn storage_changes_root(&mut self, parent_hash: &[u8]) -> Result<Option<Vec<u8>>, ()> {
+		self.inner.storage_changes_root(parent_hash)
+	}
+
+	fn storage_start_transaction(&mut self) {
+		self.inner.storage_start_transaction()
+	}
+
+	fn storage_rollback_transaction(&mut self) -> Result<(), ()> {
+		self.inner.storage_rollback_transaction()
+	}
+
+	fn storage_commit_transaction(&mut self) -> Result<(), ()> {
+		self.inner.storage_commit_transaction()
+	}
+
+	fn wipe(&mut self) {
+		self.inner.wipe()
+	}
+
+	fn commit(&mut self) {
+		self.inner.commit()
+	}
+
+	fn read_write_count(&self) -> (u32, u32, u32, u32) {
+		self.inner.read_write_count()
+	}
+
+	fn reset_read_write_count(&mut self) {
+		self.inner.reset_read_write_count()
+	}
+
+	fn get_whitelist(&self) -> Vec<TrackedStorageKey> {
+		self.inner.get_whitelist()
+	}
+
+	fn set_whitelist(&mut self, new: Vec<TrackedStorageKey>) {
+		self.inner.set_whitelist(new)
+	}
+}
+
+impl<'a, B: BlockT> ExtensionStore for WitnessExt<'a, B> {
+	fn extension_by_type_id(&mut self, type_id: TypeId) -> Option<&mut dyn Any> {
+		self.inner.extension_by_type_id(type_id)
+	}
+
+	fn register_extension_with_type_id(
+		&mut self,
+		type_id: TypeId,
+		extension: Box<dyn Extension>,
+	) -> Result<(), Error> {
+		self.inner.register_extension_with_type_id(type_id, extension)
+	}
+
+	fn deregister_extension_by_type_id(
+		&mut self,
+		type_id: TypeId,
+	) -> Result<(), Error> {
+		self.inner.deregister_extension_by_type_id(type_id)
 	}
 }
 
 fn host_storage_read(key: &[u8], value_out: &mut [u8], value_offset: u32) -> Option<u32> {
-	match with_storage(|storage| storage.get(key)) {
+	match with_externalities(|ext| ext.storage(key)) {
 		Some(value) => {
 			let value_offset = value_offset as usize;
 			let data = &value[value_offset.min(value.len())..];
@@ -378,38 +394,130 @@ fn host_storage_read(key: &[u8], value_out: &mut [u8], value_offset: u32) -> Opt
 }
 
 fn host_storage_set(key: &[u8], value: &[u8]) {
-	with_storage(|storage| storage.insert(key, value));
+	with_externalities(|ext| ext.place_storage(key.to_vec(), Some(value.to_vec())))
 }
 
 fn host_storage_get(key: &[u8]) -> Option<Vec<u8>> {
-	with_storage(|storage| storage.get(key).clone())
+	with_externalities(|ext| ext.storage(key).clone())
 }
 
 fn host_storage_exists(key: &[u8]) -> bool {
-	with_storage(|storage| storage.get(key).is_some())
+	with_externalities(|ext| ext.exists_storage(key))
 }
 
 fn host_storage_clear(key: &[u8]) {
-	with_storage(|storage| storage.remove(key));
+	with_externalities(|ext| ext.place_storage(key.to_vec(), None))
 }
 
 fn host_storage_root() -> Vec<u8> {
-	with_storage(|storage| storage.storage_root())
+	with_externalities(|ext| ext.storage_root())
 }
 
 fn host_storage_clear_prefix(prefix: &[u8]) {
-	with_storage(|storage| storage.clear_prefix(prefix))
+	with_externalities(|ext| ext.clear_prefix(prefix))
 }
 
-fn host_storage_changes_root(_: &[u8]) -> Option<Vec<u8>> {
-	// TODO implement it properly
-	None
+fn host_storage_changes_root(parent_hash: &[u8]) -> Option<Vec<u8>> {
+	with_externalities(|ext| ext.storage_changes_root(parent_hash).ok().flatten())
 }
 
 fn host_storage_append(key: &[u8], value: Vec<u8>) {
-	with_storage(|storage| storage.storage_append(key, value));
+	with_externalities(|ext| ext.storage_append(key.to_vec(), value))
 }
 
 fn host_storage_next_key(key: &[u8]) -> Option<Vec<u8>> {
-	with_storage(|storage| storage.next_key(key))
+	with_externalities(|ext| ext.next_storage_key(key))
+}
+
+fn host_storage_start_transaction() {
+	with_externalities(|ext| ext.storage_start_transaction())
+}
+
+fn host_storage_rollback_transaction() {
+	with_externalities(|ext| ext.storage_rollback_transaction().ok())
+		.expect("No open transaction that can be rolled back.");
+}
+
+fn host_storage_commit_transaction() {
+	with_externalities(|ext| ext.storage_commit_transaction().ok())
+		.expect("No open transaction that can be committed.");
+}
+
+fn host_default_child_storage_get(storage_key: &[u8], key: &[u8]) -> Option<Vec<u8>> {
+	let child_info = ChildInfo::new_default(storage_key);
+	with_externalities(|ext| ext.child_storage(&child_info, key))
+}
+
+fn host_default_child_storage_read(
+	storage_key: &[u8],
+	key: &[u8],
+	value_out: &mut [u8],
+	value_offset: u32,
+) -> Option<u32> {
+	let child_info = ChildInfo::new_default(storage_key);
+	match with_externalities(|ext| ext.child_storage(&child_info, key)) {
+		Some(value) => {
+			let value_offset = value_offset as usize;
+			let data = &value[value_offset.min(value.len())..];
+			let written = sp_std::cmp::min(data.len(), value_out.len());
+			value_out[..written].copy_from_slice(&data[..written]);
+			Some(value.len() as u32)
+		}
+		None => None,
+	}
+}
+
+fn host_default_child_storage_set(
+	storage_key: &[u8],
+	key: &[u8],
+	value: &[u8],
+) {
+	let child_info = ChildInfo::new_default(storage_key);
+	with_externalities(|ext| ext.place_child_storage(&child_info, key.to_vec(), Some(value.to_vec())))
+}
+
+fn host_default_child_storage_clear(
+	storage_key: &[u8],
+	key: &[u8],
+) {
+	let child_info = ChildInfo::new_default(storage_key);
+	with_externalities(|ext| ext.place_child_storage(&child_info, key.to_vec(), None))
+}
+
+fn host_default_child_storage_storage_kill(
+	storage_key: &[u8],
+) {
+	let child_info = ChildInfo::new_default(storage_key);
+	with_externalities(|ext| ext.kill_child_storage(&child_info))
+}
+
+fn host_default_child_storage_exists(
+	storage_key: &[u8],
+	key: &[u8],
+) -> bool {
+	let child_info = ChildInfo::new_default(storage_key);
+	with_externalities(|ext| ext.exists_child_storage(&child_info, key))
+}
+
+fn host_default_child_storage_clear_prefix(
+	storage_key: &[u8],
+	prefix: &[u8],
+) {
+	let child_info = ChildInfo::new_default(storage_key);
+	with_externalities(|ext| ext.clear_child_prefix(&child_info, prefix))
+}
+
+fn host_default_child_storage_root(
+	storage_key: &[u8],
+) -> Vec<u8> {
+	let child_info = ChildInfo::new_default(storage_key);
+	with_externalities(|ext| ext.child_storage_root(&child_info))
+}
+
+fn host_default_child_storage_next_key(
+	storage_key: &[u8],
+	key: &[u8],
+) -> Option<Vec<u8>> {
+	let child_info = ChildInfo::new_default(storage_key);
+	with_externalities(|ext| ext.next_child_storage_key(&child_info, key))
 }