Full Node Boostrap

Full Node Process Epilogue

When a full node resumes network participation, it reads consensus_seed from $HOME/.sgx_secrets/consensus_seed.sealed, does the same key derivation steps as above in steps 2-5.

1. Remote Attestation

The new full node verifies the remote attestation proof of the bootstrap node from genesis.json and creates a remote attestation proof for their own machine to show to the network that the node's Enclave is genuine.

2. Generate Registration Keypair

Using HKDF-SHA256, hkdf_salt and nonce (a 256 bit true random) a private key is derived. From registration_privkey calculate registration_pubkey

registration_privkey = hkdf({
  salt: hkdf_salt,
  ikm: Nonce-256bit ,
}); // 256 bits

registration_pubkey = calculate_curve25519_pubkey(
  registration_privkey
);

3. Authorize Full Node

The node needs to send an secretcli tx register auth transaction with the following inputs:

• The remote attestation proof the node's Enclave is genuine

• registration_pubkey

• 256 bits true random nonce

4. Network Receives Auth

On the consensus layer, inside the enclave of every full node the auth transaction comes in.

The Network validator nodes:

• Receive the secretcli tx register auth transaction

• Verify the remote attestation proof that the new node's Enclave is genuine

5. Generate seed_exchange_key

seed_exchange_key: An AES-128-SIV encryption key is used to send consensus_seed to the new node

This key is derived in several steps:

• first seed_exchange_ikm is derived using ECDH (x25519) with consensus_seed_exchange_privkey (which exists in the enclave) and registration_pubkey (which is a public identifier of the full node)

This IKM is never publicly available and protects the Secret network private entropy

seed_exchange_ikm = ecdh({
  privkey: consensus_seed_exchange_privkey,
  pubkey: registration_pubkey,
}); // 256 bits

In the second step seed_exchange_key is derived using HKDF-SHA256 from seed_exchange_ikm and nonce. When sending the seed_exchange_key to new nodes the Nonce is added as plaintext, it just serves the function of making each seed_exchange_key unique.

seed_exchange_key = hkdf({
  salt: hkdf_salt,
  ikm: concat(seed_exchange_ikm, nonce),
}); // 256 bits

6. Sharing consensus_seed with the new node

The seed_exchange_key generated in step 5 is used to encrypt the consensus_seed. The AD for this encryption algorithm is the public key of the new node: new_node_public_key All this logic is done in side the Authorization transaction. secretcli tx register auth outputs the encrypted_consensus_seed

encrypted_consensus_seed = aes_128_siv_encrypt({
  key: seed_exchange_key,
  data: consensus_seed,
  ad: new_node_public_key,
});

return encrypted_consensus_seed;

The encrypted output is received by the new full node. The new node now has access to the encrypted_consensus_seed and will have to decrypt to plaintext to receive the consensus_seed

7. New full node generates own seed_exchange_key

The AES-128-SIV encryption key seed_exchange_key is used to decrypt consensus_seed To derive this the reverse logic is followed highlighted in step 5.

First the same seed_exchange_ikm is derived using ECDH (x25519) with consensus_seed_exchange_pubkey (public in genesis.json) and registration_privkey (available only inside the new node's Enclave) This is the DH-key echange in action as this is the reverse public/private input of the IKM generation in step 5.

seed_exchange_ikm = ecdh({
  privkey: registration_privkey,
  pubkey: consensus_seed_exchange_pubkey, // from genesis.json
}); // 256 bits

seed_exchange_key is derived using HKDF-SHA256 with seed_exchange_ikm and nonce

seed_exchange_key = hkdf({
  salt: hkdf_salt,
  ikm: concat(seed_exchange_ikm, nonce),
}); // 256 bits

8. Decrypting encrypted_consensus_seed

encrypted_consensus_seed is encrypted with AES-128-SIV, seed_exchange_key as the encryption key and the public key of the registering node as the ad as the decryption additional data The new node now has all of these parameters inside its Enclave, so it's able to decrypt consensus_seed from encrypted_consensus_seed and then seal consensus_seed to disk at $HOME/.sgx_secrets/consensus_seed.sealed

consensus_seed = aes_128_siv_decrypt({
  key: seed_exchange_key,
  data: encrypted_consensus_seed,
  ad: new_node_public_key,
});

seal({
  key: "MRSIGNER",
  data: consensus_seed,
  to_file: "$HOME/.sgx_secrets/consensus_seed.sealed",
});