substraTEE is a framework for Parity Substrate, allowing to call a custom state transition function (STF) inside a Trusted Execution Environment (TEE), namely an Intel SGX enclave thereby providing confidentiality and integrity. The enclaves operate on an encrypted state which can be read and written only by a set of provisioned and remote-attested enclaves.

What substraTEE aims to enable:

  • confidential decentralized state transition functions
    • private transactions
    • private smart contracts
    • off-chain confidential personal data records (GDPR)
    • decentalized identity with selective disclosure
    • subscription-based content delivery networks
  • scalability by providing a 2nd layer to substrate-based blockchains
    • off-chain smart contracts
    • payment hubs
  • trusted chain bridges
  • trusted oracles

substraTEE is developed by Supercomputing Systems AG and has been supported by grants from the Web3 Foundation.

We also thank the teams at

Trusted Execution

We have become accustomed to the fact that we have to trust our IT administrators. While these administrators used to be in-house employees at our companies, today we often work on rented cloud platforms.

These administrators can read and modify all the data processed on any machine they manage. Unfortunately, this ability extends not only to known administrators we trust but also to hackers who can obtain administrator privileges. No company, no matter how qualified, is immune to such attacks.

Enter TEEs.

You may envision a TEE as a co-processor that manages its own cryptographic keys and only executes programs whose hash, or fingerprint, corresponds to the original code. The manufacturer of the processor guarantees, by the design of their hardware, that nobody has access to the internal keys of the TEE or can read its memory. Moreover, the manufacturer can authenticate each TEE and provide remote attestation to a user to confirm that her untampered program is actually running on a genuine TEE, even if the machine is physically located in an off-site data center.

TEEs promise, in short, integrity and confidentiality of (remote) computation. You should be aware, however, of possible security threats.

Assuming we trust TEE manufacturers’ integrity and design competence, TEEs allow us to execute any state update without sharing our data with the blockchain validator or other users. Private token transfers, private smart contracts and private state channels thus become possible and relatively cheap.

Remote Attestation


The goal of attestation is to convince a third party that a specific piece of code is running on a genuine Intel SGX HW.

convincing the substraTEE user

A user that interacts with substraTEE wants to be sure that the shielding pubkey she uses to encrypt her call to the STF originates form an enclave that

  1. is running on genuine Intel SGX HW
  2. runs the official code
  3. accesses the correct STF state

Classical Remote Attestation Solution

The standard use case for remote attestation involves a service provider (SP) like a video streaming service which wants to be sure his viewer application runs on a genuine SGX HW and respects DRM. The SP therefore requests a quote from the application and sends that quote to Intel Attestation Services (IAS) who sign off the quote if it is genuine.

The issue here is that IAS only talks to registered clients. You need to register in order to get a SPID which needs to be supplied along with requests.

Attestation Registry On-Chain

It isn't practical to ask every client to register with Intel and perform RA before every request. Therefore we'd rather let the substraTEE-worker operators attest their enclaves with IAS and write the signed quote and their certificate to the blockchain for everyone to verify.

This does change the the attestation protocol. Now the SP and the enclave in the above scheme are both running on the same machine. substraTEE-worker will itself perform an attestation protocol with its enclave and get the quote signed by IAS. Like this, only substraTEE operators need to register with IAS.

Sequence Diagram

The attestation report which is written to an on-chain registry contains:

  • enclave quote
    • report body
      • MRENCLAVE (hash of enclave build)
      • Product ID (hard-coded in substraTEE source)
      • Security Version (hard-coded in substraTEE source)
      • user data is hash of context:
        • enclave-individual signing pubkey
        • latest block hash
    • ...
  • IAS response
    • body
      • timestamp
      • enclave quote
      • ...
    • IAS certificate
    • IAS signature over above body

Any user can now verify IAS signature and MRENCLAVE (given the substraTEE enclave can be built deterministically). See the example how you can extract MRENCLAVE after building the enclave

The worker can now publish his sealing pubkey, signed with its enclave-individual signing key stated in the quote.

workers will repeat remote attestation in reasonable regular intervals (i.e. once per month)

Enclave Registry On-Chain

In order for the chain validator to be able to verify MRENCLAVE, there must be a consensus about MRENCLAVE of the valid version of substraTEE.

substraTEE developers will propose code updates to be voted on. Validators check the code and vote on behalf or against each proposal. MRENCLAVE can be reproduced by cloning the substraTEE-worker repo, building it and then:

sgx_sign dump -enclave -dumpfile out.log

TODO: we might need to provide a docker environment the achieve deterministic builds.

secret provisioning

In order to establish shared secrets among workers, they need to convince themselves mutually that they are genuine before entering some Distributed Key Generation (DKG) protocol.


provisioned secrets are sealed with Intel's SGX Sealing. Two different kinds of sealing exist. MRENCLAVE is unique for each build and each piece of HW. MRSIGNER is based on the authority of a SW vendor. The latter is practical for proprietary software because vendors can update their SW without re-provisioning secrets.

However, for decentralized open source projects, MRSIGNER cannot apply as there is no authority that could sign builds.

Therefore, enclave identity MRSIGNER must be applied.

SW updates

As SW updates will have a different measurement, the new build can't read the state that was encrypted by the old build. Local attestation allows the new version to request the provisioned secrets.

We assume reproducible builds for enclaves which should be possible with Rust subject to some assumptions. For now, watch this issue and cargo-repro.

Simplified Protocol

  1. new version's TCB hash gets voted for by onchain consensus
  2. new version registers its attestation on-chain
  3. old version shares provisioned secret with new version running on same machine by means of local (intra-platform) attestation if new version's tcb corresponds to onchain registry

See Intel's sealing paper


Intel defines different modes for running enclaves.

compilation modes: Debug, Release, Pre-Release, Simulation lanching modes: Debug, Production


Enhanced Privacy ID (EPID). A group signature key known only to the quoting enclave. Only used for remote attestation.


A Service Provider ID (SPID) is needed to talk to IAS. Developers can obtain their SPID by registering with Intel (only allows to attest DEBUG encalves!)

You can request either linkable or unlinkable quote.

tl;dr: selecting UNLINKABLE is a safe choice. But don't expect to be anonymous.

In both cases, the quoting enclave uses a group signature for a quote. You can just decide if you wish two subsequent signatures to be linkable (an observer learns "quote was signed by same platform") or not.

In any case, Intel can identify YOU by SSID as you use your SSID for remote attestation with IAS. It just doesn't learn about which HW platform the quote originates from.

Production vs. Debug Mode

Due to Intel policy, developers can only compile enclaves in Debug, Pre-Release or Simulation mode. This means that the enclave will always be launched in Debug mode which doesn't provide confidentiality as enclave memory isn't encrypted.

In order to compile enclaves in Release mode (and run them in Production mode), the SW vendor has to apply for a SGX production license. Moreover, remote attestation in production mode can only be taken out with such production license.

SCS is looking into options how to apply such policy to a decentralized system with Intel.

solution candidate

  1. A set of companies (i.e. SCS, web3 foundation) register a production license with Intel
  2. substraTEE-workers send their RA quotes to the chain.
  3. the company listens to new RA quotes and sends them to IAS with the company's SPID.
  4. the company sends the IAS report to the chain.


chaotic list of pointers:

What to use TEEs for


documentation for substraTEE, an extension of parity substrate allowing to leverage Trusted Execution Environments (TEEs) to provide integrity and confidentiality

Different ways to leverage TEEs

use casesubstraTEE-signer
(off-chain stateless)
(off-chain stateful)
hardware wallet:+1: local TEE per user:thumbsdown:
atomic swaps
(cross-chain bridge)
:+1: light node in both chains:+1::thumbsdown:
oracle:+1::+1:difficult if non-deterministic
inheritance notary:+1::+1:storage expensive
confidential transactions:thumbsdown::thumbsdown: doesn't scale? (collisions of state changes):+1: encointer
2nd layer confidential payment hub (Similar to TeeChan):+1:
confidential smart contracts:thumbsdown::+1: (Ekiden, PDO, encointer)computation time and storage expensive
POET consensus:thumbsdown::thumbsdown::thumbsdown:


off-chain: nothing special needs to be run by blockchain validators. normal transactions

stateless: no state needs to be preserved (onchain - data or hash) between uses


One flavour of substraTEE is a RPC client for substrate that runs a state transition function (STF) within a TEE (Intel SGX).

Main feature: trusted hardware custodian of your private keys

substraTEE worker

off-chain: nothing special needs to be run by blockchain validators. normal transactions

stateful: state needs to be preserved (onchain - data or hash) between uses


Similar to but still quite different than sawtooth PDO or Ekiden/OasisLabs

Do not confuse substraTEE-worker with substrate's off-chain workers. The latter are a part of the node's codebase. substraTEE worker is a standalone service interfacing substrate node using RPC or websockets

Dapps can commit WASM contracts and run their own TEE's or hire an enclave service to run confidential WASM smart contracts on. delegates are remote attested on the blockchain (the TCB doesn't include the WASM contract). They have to be fed with the most recent state, call and opaque payload. They then update the state that is written back to the chain.


on-chain: blockchain validators run confidential state transition function with every extrinsic.

stateful: state needs to be preserved (onchain - data or hash) between uses

a fork of substrate that has an Executor running in a TEE (Intel SGX)

Main feature: many confidential transactions can be executed with every block



substraTEE leverages the confidentiality guarantees of TEEs, namely Intel SGX.

Whatever is computed inside substraTEE worker enclaves can't be observed by the network nor by the operator of the worker service nor by the root user nor a cloud provider admin.

What substraTEE can't provide is network layer privacy. That's what Tor or Nym are for.


substraTEE with direct invocation is a 2nd layer technology: It allows to do state transitions without the individual transactions hitting the blockchain.

  • more transactions per second because no global consensus must be reached on individual transactions (we trust the TEEs integrity)
  • less latency because there's no need to wait for block inclusion
  • disk usage and load balancing can be scaled horizontally: substraTEE also features sharding


Chain interoperability is considered one of the more pressing challenges for blockchain technology. With substraTEE, we've built a tool that is well suited to solve trusted chain bridges, because the integrity of code execution is guaranteed by a TEE.

See our proposal for PolkaETH bridge



Example Concept for PolkaETH Bridge

substraTEE-bridge will allow to:

  • transfer ETH to a pegged token on substrate and back (PolkaETH).
  • transfer ERC-20 token on Ethereum to a pegged token on substrate and back (PolkaXYZ).
  • transfer any on-chain information between Ethereum and substrate.
  • transfer any token on Polkadot to an Ethereum ERC20 token.

substraTEE-bridge will build light clients of both chains. Block headers are stored in SGX sealed storage and transaction inclusion proofs are verified in Intel SGX enclaves. Backed value will be in custody of a set of TEEs. Correct execution is guaranteed by TEEs (Intel SGX).

In contrast to an approach like XClaim, substraTEE-bridge provides the following advantages:

  • No full collateral needed. XClaim needs vaults (or banks) to lock collateral to the amount of backed value transferred through the bridge in order to punish misbehaving vaults. Because of the opportunity cost of locked capital, this would lead to higher fees for using such a bridge. In substraTEE-bridge, SGX guarantees integrity of computation. Therefore there is no need for full collateralization.
  • No relay-contract with on-chain registry of block headers needed. Block headers are stored in the enclave's sealed storage. Less onchain storage is needed on the issuing chain.
  • Less transactions needed as there is no need for a collateralized issue commitment.

The term light client is used abiguously in the scene. We use the following definition of light client:

a light client can be viewed as a client that downloads block headers by default, and verifies only a small portion of what needs to be verified, using a distributed hash table as a database for trie nodes in place of its local hard drive (source)

Technical Concept

With regard to the document Polkadot Bridges: Design Considerations for bridging to PoW chains as well as the XClaim Paper, we intend to implement the CentralClaim Protocol with a single SGX instance as a first step (Protocols: Issue and Redeem. Transfer and Swap are off-topic). Because we leverage SGX, our CentralClaim already achieves Consistency, as there is no way to fraudulently issue PolkaETH without breaking SGX guarantees.

As pointed out in XClaim, the CentralClaim protocol doesn't achieve Redeemability nor Liveness. In contrast to Xclaim we don't suggest a punishment scheme for fraudulent vaults as they have no economic incentive to misbehave in our scheme. Instead, we implement a shared custody of locked backing chain tokens (ETH) among a set of substraTEE-bridge enclaves. The set of substraTEE-bridge instances is unpermissioned, so anyone with suitable HW can register as a substraTEE-bridge along the design of substraTEE. A threshold signature scheme is applied in order to supply Redeemability and Liveness.

The set of active substraTEE-bridge instances changes over time. Some instances will go offline, others will join. The multisig wallets will have to be updated with every mutation. One approach with improved forward security would be to generate new multisig wallets with every mutation (instead of updating members). This way TEE's that do not update their SGX platform with the most recent patches will lose access to funds as they will be rejected by the remote attestation process and therefore not be included in the new multisig set.

We also need to guarantee all-or-nothing fairness (tx1 on the backing chain and tx2 on the issuing chain are either both included or both rejected). By using a TEE, we can make sure that bridges will correctly generate tx2 upon being shown a proof of inclusion for tx1. However, we can't guarantee that tx2 is included in the other chain by relying on a single TEE as the operator could prevent tx2 from being sent to the network among other attacks. If users have many substraTEE-bridge operators to chose from, we rely on the fact that these operators have an economic incentive to follow the protocol: They can't access locked funds but they can collect fees. We only need M-of-N (configurable threshold) of these operators to play fair in order to guarantee all-or-nothing fairness.

Further hardening (including timelocked transactions) is described in the Tesseract Paper and is left for future work if security audits require it.

Reference Light Client Implementations

Substrate as well as Ethereum clients geth and parity come with the option to run as light clients (i.e. parity --light). We suggest to port ethereum parity's and substrate's light clients' validation logic into SGX enclaves. While the networking can be conventional untrusted code, the tracking of block headers as well as the validation of merkle proofs need to be performed in SGX enclaves, so the bridge operator can convince others (the receiving chain) of the validity of a statement.


Vulnerabilities in SGX may lead to total loss of locked funds as well as infinite issuance of unredeemable PolkaETH. This risk is mitigated by our M-of-N threshold signature scheme. At least M enclaves must be compromised in order to do any harm.

If remote attestation is compromised as well, fake enclaves can join the set of substraTEE-bridges and outnumber the existing set of bridges.

Related Work


Parity bridge allows an Ethereum PoA chain to bridge to the Ethereum Mainnet using contracts on both chains. The bridge is generic (arbitrary information can be passed) and bidirectional. Trust in the PoA chain validators is required.

substraTEE-bridge would replace this trust in PoA validators by trust in a single TEE or a set of TEE's (Intel SGX).


XClaim solves the bridge problem not by trusting PoA validators but by incentivized and punishable actors. However, this approach demands full collateralization and is therefore economically less attractive at scale than substraTEE-bridge.


The Tesseract Paper describes a trusted cryptocurrency exchange design using Intel SGX. In section 7 they describe a bridge protocol.

Use Case CDN Subscriptions

substraTEE could be used to restrict (narrow- or broadband) content delivery to paying users. Examples could be blogs, articles, video streaming, video on-demand, music streaming or on-deman aso.

Basic substraTEE application for CDN

  • Subscriptions are managed on-chain, as are payments (can be flat subscription fees or pay-per-use)
  • substraTEE-worker holds the content-encryption key pair (CEK). Only the worker enclave(s) can read this RSA private key. No consumers or publishers nor operators have access
  • publishers commit their content (encrypted with the CEK (RSA+AES)) to IPFS and register the content on-chain, providing the IPFS url
  • consumers request content from the substraTEE-worker over a TLS channel (can be https, wss, json-rpc, REST), which
    • authenticates the consumer and looks up subscription status on-chain
    • fetches the requested content from IPFS
    • decrypts the content
    • sends the content to the consumer over the previously established TLS channel

CEK turnover

As a first implementation, the CEK can stay constant over time. However, we should be able to rotate this key if we need to revoke.

Access to Archive Prior to Subscription

Because the private CEK is known to all worker enclaves and never needs to be known to publishers or subscribers we do not need to trans-encrypt content. It doesn't matter at what time a consumer subscribes. The worker can deliver all prior content to the subscriber. The subscription metadata can include restrictions to archive access.

Pay per use

Pay per use bears the risks of leaking private information. We'd suggest to maintain subscription balances within the worker enclave, not onchain. This way, the public doesn't learn detailed usage patterns. See our private-tx example for how this could work.


In the following we explain how substraTEE works and how the different components play together.

Direct Invocation (Vision)

vision substraTEE Target Architecture with Direct Invocation (future scenario)

  • Shielding key: used by the substraTEE-client to encrypt the call in order to protect caller privacy. It is common to all enclaves.
  • State encryption key: used to encrypt and decrypt the state storage. It is common to all enclaves.
  • Signing key: used to sign transactions for the substraTEE-node. The corresponding account must be funded in order to pay for chain fees. It is unique for every enclave.

How it works

The substraTEE-node is a substrate blockchain node with an additional runtime module:

  • substraTEE-registry module: proxies requests to workers, verifies IAS reports and keeps track of the registered enclaves. It provides the following API interfaces:
    • Register an enclave
    • Remove an enclave
    • Get the list of enclaves
    • invoke worker
    • confirm processing of requests

The substraTEE-worker checks on the first start-up if "his" enclave is already registered on the chain. If this is not the case, it requests a remote attestion from the Intel Attestation Service (IAS) and sends the report to the substraTEE-registry module to register his enclave.

If there is already an enclave (belonging to a different substraTEE-worker) registered on the chain, the substraTEE-worker requests provisioning of secrets (the shielding and state encryption private key) from the already registered enclave. The exchange of critical information between the enclaves is performed over a secure connection (TLS). The two enclaves perform a mutual remote attestation before exchanging any secrets.

Indirect Invocation (current implementation)

The high level architecture of the current implementation can be seen in the following diagram:


The main building blocks can be found in the following repositories:

  • substraTEE-node: (custom substrate node) A substrate node with a custom runtime module
  • substraTEE-worker: (client, worker-app, worker-enclave): A SGX-enabled service that performs a confidential state-transition-function

Request Lifetime end-to-end


Redundancy (M3 onwards)

The goal of redundancy is to allow multiple workers to operate on the same state to be resilient against outage of one or more workers.

The high level architecture for M3 and M4 can be seen in the following diagram:


where M3 includes only the docker image 1 and the Intel Attestation Service (IAS) and M4 includes the three docker images and the Intel Attestation Service (IAS).


substraTEE isolates confidential state from the blockchain by maintaining it off-chain and processing it in TEEs. This strategy allows application-specific sharding. Every use case can work on its own shard and even one use case could split into several shards.

By default, SubstratTEE uses the MRENCLAVE of the worker enclave as shard identifier, so in most cases, your shard is directly linked to your specific TCB and there's nothing you have to worry about.

If you want to use your TCB for more than one use case, you might want to split into shards.

Sharding UML

A single SGX HW can run many worker instances, all operating on different shards (and possibly even different TCBs).

Token Shielding

Token shielding is the process of transferring on-chain tokens (where they are transferred transparently) to off-chain STF (where transactions are private). The on-chain tokens are kept in enclave custody on a bonding account until unshielded again.

Unshielding is the reverse process, where off-chain funds are transferred to on-chain acounts. The bonding account then releases these funds on behalf of the owner's public account.

Sharding UML

substraTEE Security

The following is an overview of security aspects of substraTEE. It is neither complete nor guaranteed to be accurate. It just reflects the best of our knowledge ATM.

Intel SGX Security

The following is an overview of security aspects of substraTEE, mainly focusing on Intel SGX properties. It is neither complete nor guaranteed to be accurate. It just reflects the best of our knowledge ATM.

exploitable properties of SGX

  • An enclave has no way to control how many instances of that enclave are instantiated.
  • An enclave process can be interrupted at any point.
  • monotonic counter and trusted time provided by Platform Services (PSE) rely on Intel ME, which doesn't have a good reputation for security.

See: black hat presentation by Swami


Rollback/Replay Attack

An enclave has no way to verify that it is operating on the latest state (i.e. read from a sealed file on disk).

It cannot be assured that calls to the enclave happen sequentially. They can happen in parallel, possibly leaking secrets i.e. because a secret with weak randomness is encrypted many times with the same nonce, weakening the confidentiality.


  • monotonic counter (i.e. Intel PSE, based on ME. Not available on server HW). If you choose to trust Intel ME!
  • Blockchain registers the hash of the latest state, so a state update is only valid when it refers to the latest registered state. This doesn't solve the cause, but the symptoms.

Global State Malleability

An enclave ecall can be interrupted at any time by interrupts. Instead of returning after the interrupt, an attacker can then call the same ecall again.


  • verify-first-write-last: not only for sealed storage, but also for global state variables.

Reentrancy Attack / Global state Malleability

Can be a special case of the Rollback Attack. Similar to smart contracts reentrancy.

Explanation of reentrancy attack for smart contracts


  • verify-first-write-last

Simulator Attacks

Some emulator pretends to be an enclave.


  • Remote Attestation with IAS

Man-In-The-Middle Attack

Intel could attack a service provider by always replying to RA requests positively and put a simulated enclave as a MITM. (Intel knows, which SP is requesting a RA as it knows the SPID)



See black hat presentation by Swami at 34:50


This side-channel attack compromised both integrity and confidentiality (and therefore Remote Attestation as well). It has been fixed in Intel's recent microcode.



  • update your SGX HW
  • verify SGX is up-to-date for all substraTEE-workers (IAS tells us with their remote attestation report)

Threat model of ChainRelay


A security threat model for the ChainRelay of substraTEE.

The following points will be analysed:

  • Spoofing
  • Tampering
  • Repudiation
  • Information disclosure
  • Denial of service
  • Elevation of privileges

System overview



User of the system that holds tokens either on-chain or in an incognito account.

  • He uses the substraTEE-client
  • He can send extrinsics/transactions to the node that will then be processed by the enclave
  • He can query his own enclave state, the enclave public key and the mutual-remote-attestation port directly from a worker over WebSocket
  • He holds his keypairs (for on-chain and incognito accounts)

Worker operator

Operates the worker and the enclave.

  • He uses the substraTEE-worker
  • He has full access to the system (HW, OS and services)


Releases substraTEE software

  • He distributes SW binaries
  • He can sign enclaves with MRSIGNER

There is no specific vendor in substraTEE as it is open source code that can be deterministically built by anyone to reach an identical MRENCLAVE for the enclave. Therefore, each operator is also a vendor!

Because of this substraTEE may not use MRSIGNER policy but MRENCLAVE for SGX sealed storage (known issue! This means that sealed storage can only be accessed by the very same untampered version of the enclave running on the same HW platform.

Software updates are not yet supported:


Attack CategoryActorDescriptionMitigationAssessment
ImpersonationUserGet access to private keys of other users.Protection of keys and key stores with passwords.
WARNING: This is the responsibility of the developer building the client. Our example client does not include any mitigations.
EclipsingOperator or ISPExpose the worker to a different (malicious) nodeRely on finality and read proofs with Light-ClientOK since M6
SpoofingOperatorModify the enclave to perform malicious operationsRemote Attestation, TrustedCall signature payload includes MRENCLAVEOK
TamperingUserReplay TrustedCalls (i.e. repeat transactions of funds until account depleted)Use of nonce in TrustedCallknown issue
TamperingOperatorTamper with the block header store of the Light-Client (roll back or modify)Block header store is encrypted as SGX sealed storage
Sync with chain upon startup
Verify linked-hash-chain of block headers
TamperingOperatorTamper with the state of the enclaveState is encrypted with the state-encryption-key, the private key stored in SGX sealed storage with MRENCLAVE policyknown issue
TamperingOperatorBlock confirmations from worker to nodeRedundancy of workersOK
TamperingOperatorModify worker-api response to TrustedGetterEnclave signs responsesknown issue
RepudiationOperatorDeny WorkerApi access to certain users selectivelyRedundancy of workersOK
Information disclosureOperatorGet information about contents of TrustedCallsTrustedCalls are encrypted with public shielding key of the enclave (whose private key is stored in SGX sealed storage with MRENCLAVE policy)known issue
Information disclosureOperatorGet information about contents of TrustedGetters responsesEncrypt responses
wss:// to WorkerApi into enclave
known issue
Information disclosureOperatorGet metainformation about TrustedCallsIndirect invocation: need to use public account to proxy the TrustedCall through blockchain. Use fresh unlinkable accounts for each TrustedCall.
Direct invocation: limited access to metainformation (network layer only)
known issue
Information disclosureOperatorKnow which incognito account belongs to whomSGX confidentiality guarantees, encrypted TrustedCall and TrustedGetter with enclave shielding keyknown issue
Information disclosureOperatorLeak state informationSGX confidentiality guarantees, encrypted state with state-encryption-key
MRENCLAVE policy for SGX sealed storage
known issue
Information disclosureUserGet information about other accounts and users in the enclaveAuthentication of TrustedGetter.
User can only query own state
Denial of serviceOperatorLimit the resources of the worker or the enclave to slow down the systemRedundancy of workersOK
Denial of serviceUserSend invalid transactions to crash either the worker or the enclaveEnsure enclave code doesn't panicOK to the best of our knowledge
Denial of serviceUserOverload the system with spam (TrustedGetters or TrustedCalls)TrustedCalls: cost of tx fees (indirect invocation), Blocksize limit
TrustedGetter: load balancing as needed (scale number of workers horizontally), standard DDoS mitigations


TODO Outdated

opscall_counter_wasmcall_counterno compose_extrinsicmsg decryptioncounter updatesgx_file_readcounter update + no_ops ocall
sgx::fs::read (rsa key)
rsa msg decryption
wasm sha256 computation
wasm invokation
sgx::fs::read (aes key)
aes decryption
aes decryption
compose extrinsic
  • call_counter represents the operations that are performed in a milestone 1 counter state update.
  • call_counter_wasm represents the operations that are performed in a milestone 2 counter state update.
  • sgx::fs::read: an SGX call that accesses the sealed enclave storage which is only readable by one specific enclave instance.
  • ecall general entry point from the host system to an enclave.
  • no_ops_ocall: an ocall (a call from the enclave to the host) that does nothing in order to see the impact of an ocall itself.
  • invokations/s: stands for the number of executions per seconds that can be achieved. This does roughly correspond to tx/s.


  • RSA decryption is by far the most expensive step in the whole pipeline. This, however, is hard to migitate as long as no more efficient asymmetric encryption exists.
  • The effect of sgx::fs::read does only have a small impact.
  • wasm invokation's impact is negligible
  • If the current RSA de/-encryption process is optimized, >1000 tx/s, is achievable.


All tests have been performend on an Intel NUC NUC8i3BEH2, Bean Canyon i3-8109U 3.0 GHz.

HW Diversification

As of the time of writing, Intel SGX is the only TEE that allows remote attestation. This dependency on Intel is a single point of failure and as such undesirable for SubstraTEE.

The SubstraTEE team is investigating ways to provide remote attestation for ARM TrustZone and open source TEEs like Keystone.

Diversification would have a positive effect on TEE integrity because a vulnerability in one type of TEE would only affect a fraction of all TEEs. A pretty simple consensus algorithm could ensure integrity even in presence of large-scale attackes exploiting that vulnerability.

However, diversification could have a negative impact on confidentiality. If secrets are provisioned to several types of TEEs, it only takes a single TEE to leak the secret to compromise it for all.

Open Source Remote Attestation Process

See Distributor-Level Remote Attestation

Distributor-Level Remote Attestation

If manufaturers don't offer remote attestation, the HW distributor could jump in as the second trusted entity in the supply chain.


The goal of remote attestation is to enable the verifier to trust a member. The verifier wants to trust the hardware and software, which is physically at the member's site. The assumption is that the verifier has never accessed the hardware of the member. Therefore, other parties offer a root of trust, which is implanted in the hardware. In the picture below are three other parties, where most important one is the provision entity. She is a distributor of hardware and has also the ability to program the devices. So, they take hardware from the official manufacturers and combine it with software from a source, which is trusted by the verifier. Afterwards, this bundle is purchasable by everyone, who wants to participate. In conclusion, if somebody wants to become a member of the service, he has to buy a device from provision entity. These devices are ready to perform remote attestation.


The verifier is concerned about integrity and confidentiality and requires a proof that:

  1. Member’s hardware is genuine, attested by the provision entity in a manner that the verifier is able to identify devices in the field by secure cryptographic methods
  2. Member’s hardware runs exactly the code as published open source by the Trusted Software Source
  3. Data supplied to the TEE is treated confidentially

To fulfill these requirements each role is specified in the following sections.


  • Hardware Manufacturer: produces hardware
  • Trusted Software Source: writes open source software that is supposed to be run on TEEs
  • Provision Entity: Distributor with the possibility to provision devices
  • Member: operates TEE hardware on their own premises and always has physical access to it
  • Verifier: wants to run software from the Trusted Software Source with its own confidential data on member's hardware

Hardware Manufacturer

The hardware manufacturer has to be trusted.

Trusted Software Source

To generate an open source flash image, which is signed, is problematic. Because the one who is signing is a new root of trust. Therefore, in this concept this root is spread over a multiple participants to get to an open source like root of trust. The parties should be as independent as possible. The diagram below visualizes our approach. On the left side is the open source code visible for everyone. Everything that follows is constructed under the assumption that the parties have established secure communication channels. All parties (Web3, SCS, ...) collaborate in the Multi-Party-Computation (MPC) RSA generation. As a result, everyone receives the public key and a part of the private key. Therefore, they can only together generate a signature. This is used to build a binary that only can be signed by all parties together. They take the source code and build it deterministically. Afterwards, they sign their binary and exchange it with each other. Then, they check the binaries from the other parties, if they are the same, they combine the signatures to the final signature. This signature can be verified with the public key.


Provision Entity

The provision entity has the task to prepare the devices for remote attestation. This makes her the main root of trust. Therefore she has to be trustworthy and she also needs appropriate hardware. Which means that she needs at least HSM (Hardware Security Module). Better she has an access authorisation system for the facilities. To provision devices, the provision entity has to execute the following steps.

  • Get hardware from the hardware manufacturer
  • Get the software from the trusted software source
  • Check the hardware and the software
  • Enable secure boot
  • Generate the attestation data
  • Sell the devices publicly


The first two steps are obvious. Get the hard and software from the corresponding sources. The next step is important. The provision entity has to check, if the hardware is not tampered. Because later, with her signature, she states that the hardware is trustworthy.

The next step is to enable secure boot. This means that the provision entity takes the public key from the trusted software source (the one generated in the MPC process) burn it into the devices. Also eFuses are burnt to harden the device. This step is hardware dependent. In some devices only the hash of this public key is burnt in, but its enough to enable secure boot. In the literature this key is often referred as the vendor key.

Afterwards, the attestation data is made. The provision entity generates with the HSM a per device unique key pair. This key pair is called the Attestation Identifier Key, because it is used to identify the device for attestation. Then also a device unique key called Endorsement Key (EK) is used. The origin of this key is hardware dependent. In some devices this key is already embedded in the device. And in others the key can be chosen and written to OTP (One Time Programmable Memory). Where it is impossible to read it back and only accessible through the on chip crypto engine. The EK is then used to encrypt the private part of the AIK. Then the public AIK and the encrypted private AIK are signed with the provision entity Key (PE-Key). These three parts form the attestation data.

The PE-Key is certified by a root CA and the public part of this key has to be publicly available. The verifier later needs this key.

The attestation data is added to the device. Because the attestation data is not confidential. It can be saved anywhere on the device.

Another important point is that the provision entity has to guarantee that she forget the EK and the AIK. In some devices the provision entity has never access to the EK. This is good nor bad, because it just shifts trust from the provision entity to the hardware manufacturer.

The last step is to sell the provisioned devices to people who want to operate the hardware. They are called members, because they can become a part of the network.



The member buys a device from the provision entity. This device can only boot from signed images, which are signed by the trusted software source. These images then perform a secure boot. This image sets up a system, that is split in two halves. In one half starts a rich OS, which is considered untrusted. In the other half starts a secure OS. This half is protected from the other side with ARM Trust Zone. The secure OS such as OPTEE, is able to host different TEEs in parallel and ensures encapsulation of these TEEs.



To do an actual remote attestation, the verifier needs at first the public key from the provision entity. Then the verifier waits on request from the member. When he wants to join, he send his request, the attestation data. The verifier then validates the attestation data. If the data is valid, he knows the public AKI. To validate the public AIK, he generates a challenge. The simplest challenge is a random number. This number is sent to the member. The member decrypts the private AIK and signs the random number with it. Afterwards he sends the signature back with some system measurements. The verifier can validate the signature. If the signature is valid, the verifier can make the following assumptions:

  1. The private AIK used to forge the signature belongs to the public AIK from the attestation data, therefore there a valid key pair
  2. The AIK was generated by the provision entity, because it is signed with the PE-Key
  3. The device is a provisioned hardware, because the hardware is the only one which knows the EK and is able to decrypt the private AIK.
  4. The hardware has booted a trustful system, because the eFuses were burnt by the provision entity



Here you'll find some hands-on tutorials on how to use substraTEE for your use case

How to Build and Run a substraTEE-node

You don't need SGX to run a node (only workers do).


Install Rust:

curl -sSf | sh

In order to compile ring into wasm, you'll need LLVM-9 or above or you'll get linker errors. Here the instructions for Ubuntu 18.04

chmod +x
sudo ./ 10
export CC=/usr/bin/clang-10
export AR=/usr/bin/llvm-ar-10
# if you already built, make sure to run cargo clean

Initialize your Wasm Build environment:


Build Wasm and native code:

cargo build --release

with docker

If you prefer to skip the setup, you can just use our docker and build the node like this (run in the repo root):

docker pull scssubstratee/substratee_dev:18.04-2.9.1-1.1.2
docker run -it -v $(pwd):/root/work scssubstratee/substratee_dev:18.04-2.9.1-1.1.2 /bin/bash
cargo build --release


Single Node Development Chain

Purge any existing developer chain state:

./target/release/substratee-node purge-chain --dev

Start a development chain with:

./target/release/substratee-node --dev

If you want the substraTEE-node to expose a different websocket port, use the option --ws-port xxx. If external workers or clients need to access, add the option --ws-external.

Detailed logs may be shown by running the node with the following environment variables set: RUST_LOG=debug RUST_BACKTRACE=1 cargo run -- --dev.

Node as a System Service

If you want to run your node as a system service in Linux, create (as root or user with sudo permissions) a file in /etc/systemd/system called substraTEE-node.service with the following content:

Description=SubstraTEE Node

ExecStart=<ABSOLUTE PATH TO>/substratee-node --chain <PATH TO CHAIN JSON> --name <NAME OF THE NODE>



  • StartLimitIntervalSec makes that systemd will try to re-start the service forever.
  • RestartSec indicates the interval between two restarts.
  • User specifies the user that should run the node.
  • ExecStart specifies the path to the binary. Use absolute paths here.

Update the systemd daemon with systemctrl daemon-reload.

Use the following commands:

  • systemctrl start substraTEE-node.service to start the node.
  • systemctrl stop substraTEE-node.service to stop the node.
  • systemctrl status substraTEE-node.service to check the status of the node/service.

How To Run Your Own Worker

HW requirements

While SGX is supported by most Intel CPU's that is not the case for all chipsets. Here we're just telling you what HW we are using and is known to work.

Dell PowerEdge R340 Server

CPU has to be Intel(R) Xeon(R) E-2276G CPU @ 3.80 GHz

Enable SGX support in BIOS

To enable SGX support in the Dell BIOS, enter the BIOS, go to System Security and set the following values:

  • Intel SGX to On
  • SGX Launch Control Policy to Unlocked

Intel SGX development and production (commercial) license

In order to perform a remote attestation of the enclave, an Intel SGX Attestation Enhanced Service Privacy ID (EPID) is needed. We use unlinkable quotes in our code. Developers need to register an account with Intel

Development Access

Copy your SPID and key to the following files (use Linux line endings):

  • bin/spid.txt: SPID of your subscription
  • bin/key.txt: Key of your subscription (primary or secondary works)

The enclave will be signed with the development key found under enclave/Enclave_private.pem and uses the configuration found under enclave/Enclave.config.xml.

Production Access

You need a commercial license with Intel to run your enclaves in production mode (the only mode that really is confidential). Only legal entities can get a commercial license with Intel. Get in touch with them to obtain one.

Copy your SPID and key to the following files (use Linux line endings):

  • bin/spid_production.txt: SPID of your subscription
  • bin/key_production.txt: Key of your subscription (primary or secondary works)

These files are used to access the Intel Remote Attestation Service.

The enclave will be signed with the private key that was also registered and whitelisted at Intel's (in the process of obtaining a commercial license). Make sure that the key is exported as an environment variable called SGX_COMMERCIAL_KEY.

The enclave in production mode uses the configuration found under enclave/Enclave.config.production.xml.

The only difference is that the option DisableDebug is set to 1.

SW Requirements

You need the following components installed to start developing/compiling the code:

Setup SGX hardware with Ansible

You find a sample Ansible playbook here

Open the playbook with your editor and replace all the variables with <...> with your own settings.

To execute the playbook and configure the remote machine, use the following command:

ansible-playbook site.yml -k

Using Docker

We provide docker images with all the required tools installed. They can be found on dockerhub.

The tag has the following format: <Ubuntu version>-<Intel SGX SDK version>-<Rust SGX SDK version>. We don't provide any latest so you must specify the tag.

If you execute

docker pull scssubstratee/substratee_dev:1804-2.12-1.1.3-001

you get a docker image with

  • Ubuntu 18.04
  • Intel SGX SDK 2.12
  • Rust SGX SDK 1.1.3 (which includes the correct Rust version)
  • container version 001
  • IPFS 0.4.21

The following builds the code inside the docker, but the compiled binaries are stored on your local working copy.

docker run -it -v $(pwd):/root/work scssubstratee/substratee_dev:1804-2.12-1.1.3-001 /bin/bash

Now you can build and run your worker inside docker.

Enabling SGX HW Support in Docker

If you are on a platform that supports SGX, you can enable HW support by:

  • Enable the SGX support in the BIOS

  • Instal the Intel SGX Driver and the Intel SGX SDK and make sure that /dev/isgx appears

  • Start the docker with SGX device support:

    docker run -it -v $(pwd):/root/work --device /dev/isgx scssubstratee/substratee_dev:1804-2.12-1.1.3-001 /bin/bash
  • Start the aesm service inside the docker:

    LD_LIBRARY_PATH=/opt/intel/sgx-aesm-service/aesm/ /opt/intel/sgx-aesm-service/aesm/aesm_service &
  • Compile the substraTEE-worker:

  • run worker like described below

If you run the Hardware Mode on a platform that does not support SGX, you get the following error from the substraTEE-worker

*** Start the enclave
[2019-05-15T05:15:03Z ERROR substratee_worker::enclave_wrappers] [-] Init Enclave Failed SGX_ERROR_NO_DEVICE!

Build Worker

In order to compile ring into wasm, you'll need LLVM-9 or above or you'll get linker errors. Here the instructions for Ubuntu 18.04. Skip this if you're building in our docker.

chmod +x
sudo ./ 10
export CC=/usr/bin/clang-10
export AR=/usr/bin/llvm-ar-10
# if you already built, make sure to run cargo clean
git clone
cd substraTEE-worker

this might take 10min+ on a fast machine.

then you'll have to provide your SPID and KEY (see above)

echo "<YOUR SPID>" > bin/spid.txt
echo "<YOUR KEY>" > bin/key.txt

Run Worker

cd bin
./substratee-worker init-shard
./substratee-worker shielding-key
./substratee-worker signing-key
./substratee-worker run --ns <yournodeip>

How to Perform Private Transactions

Private transactions are a change of ownership of tokens where no one but the involved parties can learn who sent how many tokens to whom.

Substrate blockchains are usually account-based and pseudonymous by nature: The whole world can see all transactions and their source, destination and amount. substraTEE offers confidentiality in a similar way that Zcash does: it offers users a way to move their tokens into a dark pool (shielding process) where they can transact privately and later retrieve tokens on their public accounts (unshielding). In the case of Zcash, privacy is guaranteed by zk-SNARKS, in substraTEE it is guaranteed by TEEs.

The detailed design of the shielding and unshielding process is described in the chapter Token Shielding.

In the following demo we show how Alice can send tokens to Bob privately. The demo will run in our docker container so you don't need to setup a complete SGX development machine (although the Intel SGX driver and SDK needs to be installed making /dev/isgx and the aesm service available).


You'll need SGX enabled hardware and to register with Intel and obtain your own SPID and KEY.

Build worker, client and node in our docker:

# get the docker image
# check for updates on
docker pull scssubstratee/substratee_dev:18.04-2.9.1-1.1.2

# create a dedicated demo directory and start the docker container
mkdir demo && cd demo
docker run -it -v $(pwd):/root/work -v /var/run/aesm:/var/run/aesm --device /dev/isgx scssubstratee/substratee_dev:18.04-2.9.1-1.1.2 /bin/bash

# now you are inside the container
# clone and build the worker and the client
# info: change the tag to the latest
cd work
git clone
cd substraTEE-worker
git checkout v0.6.12-sub2.0.0
# this might take 10min+ on a fast machine

# use your SPID and KEY from Intel
echo "<YOUR SPID>" > bin/spid.txt
echo "<YOUR KEY>" > bin/key.txt

# clone and build the node
# info: change the tag to the latest
cd ..
git clone
cd substraTEE-node
git checkout v0.6.12-sub2.0.0
cargo build --release
# another 10min

For a nicer overview of the demo, let's install tmux and split our docker console into multiple terminals

apt update
apt install -y tmux
tmux split-window -v
tmux split-window -h

You should now see three terminals

Launch node in terminal 1

cd ~/work/substraTEE-node/
./target/release/substratee-node --dev -lruntime=debug

blocks should be produced...

Launch worker in terminal 2

use Ctrl-B + cursors to move between terminals

cd ~/work/substraTEE-worker/bin
./substratee-worker init-shard
./substratee-worker shielding-key
./substratee-worker signing-key
./substratee-worker run

Play in terminal 3

cd ~/work/substraTEE-worker/client

Now you can watch the process of

  1. Alice creating a new incognito account. This account is never disclosed to the public.
  2. Alice shielding funds onto her incognito account
  3. Alice privately sending funds to Bobs incognito account
  4. Alice unshielding some funds back onto her public account


The files created in the docker container belong to root. This makes it hard to delete them on your normal system. We now give them back to your standard user.

Note: This step is optional.

cd /root/work
ls -la

# write down the numbers on the line containing '.'
# example output: drwxrwxr-x 17 1002 1002   4096 Nov  2 15:10 .
#  where the numbers are 1002 (NUMBER1) and 1002 (NUMBER2)

# give all files back to the external user
chown -R <NUMBER1>:<NUMBER2> substraTEE-worker substraTEE-node

How To Access On-Chain Storage From Within The Enclave Trustlessly

substraTEE isolates confidential state (what the STF TrustedCall operates on inside the SGX enclave) from on-chain state (what is plaintext readable by the entire network of substraTEE-nodes). Some use cases, however, reqire read access to on-chain storage for their TrustedCalls. As the enclave can't trust it's worker service, it has to request and verify read proofs from the substraTEE-node.

Our goal is that you can use the same pallets that you use on-chain also inside substraTEE enclaves. Therefore, we are mapping storage keys directly between confidential state and on-chain state. Your TrustedCall has to specify what storage keys it requires and these will be mapped to the confidential state befor executing the call.

For this to work, the sgx-runtime must be compatible with the node-runtime. This means that the same substrate version must be used. However, it does not mean that the same pallets must be instantiated.

Until #113 is resolved, we also have the restriction that StorageMap and StorageDoubleMap must use StorageHasher::Blake2_128Concat.

Trusted Time Example

Inside the enclave we don't have a trusted time source (We could use Intel's AESM with sgx_get_trusted_time but that would extend our trust assumptions). The blockchain delivers trusted time because every block includes a UTC timestamp which is agreed upon by consensus (within a certain tolerance).

For this example, we access on-chain time using substrate's timestamp pallet. More precisely, we will enable you to call Timestamp::<T>::now() from any pallet in your STF. You will get the UTC timestamp from the block that includes your TrustedCall.

Key Mapping

In your STF, you'll have to define what on-chain storage keys shall be mapped for each TrustedCall:

fn main() {
pub fn get_storage_hashes_to_update(call: &TrustedCall) -> Vec<Vec<u8>> {
    let mut key_hashes = Vec::new();
    match call {
        TrustedCall::your_time_aware_call(_) => {
        // more calls ....

In your pallet you can now query timestamp as usual

fn main() {
decl_module! {
    pub struct Module<T: Trait> for enum Call where origin: T::Origin {
        #[weight = 10_000]
        pub fn your_time_aware_call(origin) -> dispatch::DispatchResult {
            ensure!(Timestamp::<T>::now() > EARLIEST_TIME_OF_EXECUTION,
                "too early to call this");
            // ...

How To Build Your Own Trusted STF

substraTEE is a framework that makes it easy for you to gain confidentiality for your decentralization endeavours.

The development process integrates well with substrate:

  1. develop and debug your use case on substrate, writing your own pallets
  2. Once the logic works, move your sensitive pallets to substraTEE without modification and you'll get confidential state (and state updates)

In the following we will assume that you know how to build custom substrate blockchains and we will skip boring explanations.

Example Use Case Encointer

We will walk you through this process with a real-world example: Encointer

Encointer has been developed as a substrate chain with 4 custom pallets added to the node-template:


We will now show you how we can turn Testnet Gesell (all public) in to Testnet Cantillon, featuring confidentiality for sensitive pallets.

In order to protect the privacy of users we will move the balances and ceremony pallets into the substraTEE-enclave. These pallets will still need to interact with the on-chain state, as indicated in the diagram below:


The final code can be inspected on encointer github

TEE Runtime

Substrate chains wrap all their business logic into a runtime made up of pallets. substraTEE does so too, so let's create our TEE runtime:

git clone

this is actually a fork of node-template, stripped from everything we don't need for our case.

Now we need to include our pallets balances and ceremonies exactly the way you're used to from substrate


fn main() {
    pub enum Runtime where
        Block = Block,
        NodeBlock = opaque::Block,
        UncheckedExtrinsic = UncheckedExtrinsic
        System: system::{Module, Call, Config, Storage, Event<T>},
        Timestamp: timestamp::{Module, Call, Storage, Inherent},
        Balances: balances::{Module, Call, Storage, Config<T>, Event<T>},
        TransactionPayment: transaction_payment::{Module, Storage},
        Sudo: sudo::{Module, Call, Config<T>, Storage, Event<T>},
        EncointerCeremonies: encointer_ceremonies::{Module, Call, Storage, Config<T>, Event<T>},
        EncointerBalances: encointer_balances::{Module, Call, Storage, Event<T>},

Looks familiar? If not, learn from the best

We will skip the nitty gritty of including your pallets.


The blockchain we'll be using is based on parity's node-template with one substraTEE-specific pallet that will take care of the worker registry and will proxy TrustedCalls

git clone

Encointer will add its public pallets to this node tempalte: scheduler and currencies. See encointer-node


The substraTEE-worker is the service running on a Intel SGX enabled machine. It will run our TEE-runtime inside an SGX enclave, operating on encrypted state.

The worker will also be our ChainRelay, a trustless bridge from the blockchain into the SGX enclave.

The worker itself will not need to be modified, it is the framework which runs your custom STF logic. It also offers you a customizable CLI interface


Now we need a way to call our custom pallet functions isolated in a TEE.

substraTEE encapsulates all the application-specific stuff in its substratee-stf crate that you can customize.

git clone

Let's start by defining a new TrustedCall:


fn main() {
#[derive(Encode, Decode, Clone)]
pub enum TrustedCall {
    balance_transfer(AccountId, AccountId, CurrencyIdentifier, BalanceType),
    ceremonies_register_participant(AccountId, CurrencyIdentifier, Option<ProofOfAttendance<MultiSignature, AccountId32>>)

impl TrustedCall {
    fn account(&self) -> &AccountId {
        match self {
            TrustedCall::balance_transfer(account, _, _, _) => account,
            TrustedCall::ceremonies_register_participant(account, _, _) => account,


Important: The first argument of each TrustedCall has to be the incognito AccountId which will sign the TrustedCallSigned which will then be encrypted and sent to the worker through the blockchain as a proxy.

Now that we defined a new call we need to execute it:


fn main() {
    pub fn execute(ext: &mut State, call: TrustedCall, _nonce: u32, calls: &mut Vec<OpaqueCall>) {
        ext.execute_with(|| {
            let _result = match call {
                TrustedCall::balance_transfer(from, to, cid, value) => {
                    let origin = sgx_runtime::Origin::signed(AccountId32::from(from));
                    sgx_runtime::EncointerBalancesCall::<Runtime>::transfer(AccountId32::from(to), cid, value)
                TrustedCall::ceremonies_register_participant(from, cid, proof) => {
                    let origin = sgx_runtime::Origin::signed(AccountId32::from(from));
                    sgx_runtime::EncointerCeremoniesCall::<Runtime>::register_participant(cid, proof)

Now you see that TrustedCall::ceremonies_register_participant() calls register_participant() in our ceremonies pallet.

This function call depends on the scheduler and currencies pallets which are not present in our TEE runtime. It is on-chain. So we need to tell substraTEE that it needs to fetch on-chain storage (and verify a read-proof) before executing our call:


fn main() {
    pub fn get_storage_hashes_to_update(call: &TrustedCall) -> Vec<Vec<u8>> {
        let mut key_hashes = Vec::new();
        match call {
            TrustedCall::balance_transfer(account, _, _, _) => { },
            TrustedCall::ceremonies_register_participant(account, _, _) => {
                key_hashes.push(storage_value_key("EncointerScheduler", "CurrentPhase"));
                key_hashes.push(storage_value_key("EncointerScheduler", "CurrentCeremonyIndex"));
                key_hashes.push(storage_value_key("EncointerCurrencies", "CurrencyIdentifiers"));

See How to access on-chain storage for more details.

Important: Make sure your on-chain runtime and TEE runtime depend on the same version of substrate. Otherwise, mapping storage keys between the two runtimes might fail.

Finally, we will extend our CLI client to allow us to call our function:


fn main() {
                .description("register participant for next encointer ceremony")
                .options(|app| {
                            .help("AccountId in ss58check format"),
                .runner(move |_args: &str, matches: &ArgMatches<'_>| {
                    let arg_who = matches.value_of("accountid").unwrap();
                    let who = get_pair_from_str(matches, arg_who);
                    let (mrenclave, shard) = get_identifiers(matches);
                    let tcall = TrustedCall::ceremonies_register_participant(
                        shard, // for encointer we assume that every currency has its own shard. so shard == cid
                    let nonce = 0; // FIXME: hard coded for now
                    let tscall =
                        tcall.sign(&sr25519_core::Pair::from(who), nonce, &mrenclave, &shard);
                        "send trusted call register_participant for {}",
                    perform_operation(matches, &TrustedOperationSigned::call(tscall));

This will allow us to call

 encointer-client trusted register-participant //AliceIncognito --mrenclave Jtpuqp6iA98JmhUYwhbcV8mvEgF9uFbksWaAeyALZQA --shard 3LjCHdiNbNLKEtwGtBf6qHGZnfKFyjLu9v3uxVgDL35C

The --mrenclave identifies the TCB while --shard identifies the local currency we're registering for.


As you may have guessed by now, Encointer uses sharding. Encointer maintains a global registry of local currencies on-chain (with the currencies pallet). The balances for each local currency are maintained confidentially within substraTEE. One shard for each currency. This means that a worker has to decide what shard it operates on.

See Sharding for more details.


Now that everything is super-isolated and confidential, how should we know if our call actually worked?

That's why substraTEE-worker exposes a websocket interface for encrypted and authenticated queries.

We will now implemet a getter that can only be called by the AccountId it refers to.


fn main() {
#[derive(Encode, Decode, Clone)]
pub enum TrustedGetter {
    balance(AccountId, CurrencyIdentifier),
    ceremony_registration(AccountId, CurrencyIdentifier)

impl TrustedGetter {
    pub fn account(&self) -> &AccountId {
        match self {
            TrustedGetter::balance(account, _) => account,
            TrustedGetter::ceremony_registration(account, _) => account,

Again, the first argument specifies the AccountId that is allowed to read its part of the state, authenticated by a signature.


fn main() {
    pub fn get_state(ext: &mut State, getter: TrustedGetter) -> Option<Vec<u8>> {
        ext.execute_with(|| match getter {
            TrustedGetter::balance(who, cid) => {
                Some(get_encointer_balance(&who, &cid).encode())
            TrustedGetter::ceremony_registration(who, cid) => {
                Some(get_ceremony_registration(&who, &cid).encode())

fn get_ceremony_registration(who: &AccountId, cid: &CurrencyIdentifier) -> ParticipantIndexType {
    let cindex = match sp_io::storage::get(&storage_value_key(
        "CurrentCeremonyIndex")) {
            Some(val) => if let Ok(v) = CeremonyIndexType::decode(&mut val.as_slice()) { v } else { 0 },
            None => 0
    info!("cindex = {}", cindex);
    if let Some(res) = sp_io::storage::get(&storage_double_map_key(
    )) {
        if let Ok(pindex) = ParticipantIndexType::decode(&mut res.as_slice()) {
        } else {
            debug!("can't decode ParticipantIndexType for {:x?}", res);
    } else {
        debug!("no registration for caller");

Note: Currently, the stf is not aware of the runtime metadata, so we have to hard-code hashers for StorageMap and StorageDoubleMap.

Again, we will introduce our getter in the CLI:


fn main() {
        .description("query state if registration for this ceremony")
        .options(|app| {
                    .help("AccountId in ss58check format"),
        .runner(move |_args: &str, matches: &ArgMatches<'_>| {
            let arg_who = matches.value_of("accountid").unwrap();
            println!("arg_who = {:?}", arg_who);
            let who = get_pair_from_str(matches, arg_who);
            let (mrenclave, shard) = get_identifiers(matches);
            let tgetter =
                TrustedGetter::ceremony_registration(sr25519_core::Public::from(who.public()), shard);
            let tsgetter = tgetter.sign(&sr25519_core::Pair::from(who));
            let res = perform_operation(matches, &TrustedOperationSigned::get(tsgetter));
            let ind = if let Some(v) = res {
                if let Ok(vd) = ParticipantIndexType::decode(&mut v.as_slice()) {
                } else {
                    info!("could not decode value {:x?}", v);
            } else {
            println!("{}", ind);

So we can query our index in the particpant registry with our CLI

encointer-client trusted ceremony-registration //AliceIncognito --mrenclave Jtpuqp6iA98JmhUYwhbcV8mvEgF9uFbksWaAeyALZQA --shard 3LjCHdiNbNLKEtwGtBf6qHGZnfKFyjLu9v3uxVgDL35C

Happy coding!



MilestoneRequest InvocationSTF# Workers per STFOn-chain tx per invocationread chain state from STFSupported TEE Manufact.Remote Attestation Registry
M1 ☑ProxyRust12-Intel-
M2 ☑ProxyRust or WASM12-Intel-
M3 ☑ProxyRust or WASM12-IntelX
M4 ☑ProxyRust or WASMN (redundant)1+N-IntelX
M5 ☑ProxyRust modularN (redundant)1+N-IntelX
M6+M7 ☑ProxyRust modularN (redundant)1+NXIntelX
future ☐ProxyRust or InkN (redundant)2XIntel + ARM TrustZone + Keystone (?)X
future ☐DirectRust or InkN (master + failover)<< 1XIntel + ARM TrustZone + Keystone (?)X

M1 PoC1: single-TEE confidential state transition function

off-chain worker runs STF within an Intel SGX enclave. The state is persisted in a sealed file which can only be read by that very enclave.

The demo STF will be a simple counter.

M2 PoC2: single-TEE confidential state transition function in WASM

In addition to M1, the STF is defined by WASM code which is run by a WASMI interpreter within an Intel SGX enclave.

The demo STF will be a simple counter.

M3 Remote Attestation Registry

substraTEE-worker can remote-attest its own enclave with Intel Attestation Service (IAS). The report signed by IAS is then registered on-chain with substraTEE-registry runtime module. Users can verify a worker’s IAS report before interacting with it. So they can be certain that the correct code is running on a genuine SGX CPU.

M4 Redundancy and Secret Provisioning

Several substraTEE-workers running on different machines can redundantly operate on the same STF. This guarantees that the STF survives the loss of a few SGX machines (going offline, breaking down, denial-of-service). Moreover, this improves integrity guarantees as all the workers register call receipts including the hash of the new state. A single compromised enclave can therefore only break confidentiality, but not integrity, as manipulation would be evident to anyone. Secret sharing among a dynamic set of worker enclaves must be implemented for such redundancy.

M5 Modular STF with private-tx example

Since M5, the STF is modular and has its own crate which can easily be swapped. An example for private transactions has been added

M6 read chain state from STF

From M6 onwards, substraTEE STF can access chain state in a trustless way. A substrate light client verification logic will be included in the worker enclave that allows the STF to query chain state by means of subscribing to storage over RPC and verifying returned values within the enclave.


support for ink contracts

(development not yet funded)

ink! is substrate's domain specific contract language on top of Rust. This milestone shall bring ink! contracts to substraTEE.


  • direct invocation
  • performance benchmarks and optimization
  • testnet for stress-tests and showcasing
  • use cases: bridges, payment hubs, ...


IASIntel Attestation Services
MRENCLAVEenclave measurement (basically the hash of your enclave binary)
palleta module for substrate runtimes
runtimethe business logic of a substrate blockchain
SCSSupercomputing Systems AG
SGXIntel's Software Guard Extensions
STFState Transition Function
TCBTrusted Computing Base
TEETrusted Execution Environment