openethereum/secret-store/src/key_server.rs

// Copyright 2015-2020 Parity Technologies (UK) Ltd.
// This file is part of OpenEthereum.

// OpenEthereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// OpenEthereum is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with OpenEthereum.  If not, see <http://www.gnu.org/licenses/>.

use super::{acl_storage::AclStorage, key_server_set::KeyServerSet, key_storage::KeyStorage};
use crypto::DEFAULT_MAC;
use ethkey::crypto;
use key_server_cluster::{
    math, new_network_cluster, ClusterClient, ClusterConfiguration as NetClusterConfiguration,
    NetConnectionsManagerConfig,
};
use parity_runtime::Executor;
use parking_lot::Mutex;
use std::{collections::BTreeSet, sync::Arc};
use traits::{
    AdminSessionsServer, DocumentKeyServer, KeyServer, MessageSigner, NodeKeyPair,
    ServerKeyGenerator,
};
use types::{
    ClusterConfiguration, EncryptedDocumentKey, EncryptedDocumentKeyShadow,
    EncryptedMessageSignature, Error, MessageHash, NodeId, Public, RequestSignature, Requester,
    ServerKeyId,
};

/// Secret store key server implementation
pub struct KeyServerImpl {
    data: Arc<Mutex<KeyServerCore>>,
}

/// Secret store key server data.
pub struct KeyServerCore {
    cluster: Arc<dyn ClusterClient>,
}

impl KeyServerImpl {
    /// Create new key server instance
    pub fn new(
        config: &ClusterConfiguration,
        key_server_set: Arc<dyn KeyServerSet>,
        self_key_pair: Arc<dyn NodeKeyPair>,
        acl_storage: Arc<dyn AclStorage>,
        key_storage: Arc<dyn KeyStorage>,
        executor: Executor,
    ) -> Result<Self, Error> {
        Ok(KeyServerImpl {
            data: Arc::new(Mutex::new(KeyServerCore::new(
                config,
                key_server_set,
                self_key_pair,
                acl_storage,
                key_storage,
                executor,
            )?)),
        })
    }

    /// Get cluster client reference.
    pub fn cluster(&self) -> Arc<dyn ClusterClient> {
        self.data.lock().cluster.clone()
    }
}

impl KeyServer for KeyServerImpl {}

impl AdminSessionsServer for KeyServerImpl {
    fn change_servers_set(
        &self,
        old_set_signature: RequestSignature,
        new_set_signature: RequestSignature,
        new_servers_set: BTreeSet<NodeId>,
    ) -> Result<(), Error> {
        let servers_set_change_session = self.data.lock().cluster.new_servers_set_change_session(
            None,
            None,
            new_servers_set,
            old_set_signature,
            new_set_signature,
        )?;
        servers_set_change_session
            .as_servers_set_change()
            .expect("new_servers_set_change_session creates servers_set_change_session; qed")
            .wait()
            .map_err(Into::into)
    }
}

impl ServerKeyGenerator for KeyServerImpl {
    fn generate_key(
        &self,
        key_id: &ServerKeyId,
        author: &Requester,
        threshold: usize,
    ) -> Result<Public, Error> {
        // recover requestor' public key from signature
        let address = author
            .address(key_id)
            .map_err(Error::InsufficientRequesterData)?;

        // generate server key
        let generation_session = self.data.lock().cluster.new_generation_session(
            key_id.clone(),
            None,
            address,
            threshold,
        )?;
        generation_session
            .wait(None)
            .expect("when wait is called without timeout it always returns Some; qed")
            .map_err(Into::into)
    }

    fn restore_key_public(
        &self,
        key_id: &ServerKeyId,
        author: &Requester,
    ) -> Result<Public, Error> {
        // recover requestor' public key from signature
        let address = author
            .address(key_id)
            .map_err(Error::InsufficientRequesterData)?;

        // negotiate key version && retrieve common key data
        let negotiation_session = self
            .data
            .lock()
            .cluster
            .new_key_version_negotiation_session(*key_id)?;
        negotiation_session
            .wait()
            .and_then(|_| negotiation_session.common_key_data())
            .and_then(|key_share| {
                if key_share.author == address {
                    Ok(key_share.public)
                } else {
                    Err(Error::AccessDenied)
                }
            })
            .map_err(Into::into)
    }
}

impl DocumentKeyServer for KeyServerImpl {
    fn store_document_key(
        &self,
        key_id: &ServerKeyId,
        author: &Requester,
        common_point: Public,
        encrypted_document_key: Public,
    ) -> Result<(), Error> {
        // store encrypted key
        let encryption_session = self.data.lock().cluster.new_encryption_session(
            key_id.clone(),
            author.clone(),
            common_point,
            encrypted_document_key,
        )?;
        encryption_session.wait(None).map_err(Into::into)
    }

    fn generate_document_key(
        &self,
        key_id: &ServerKeyId,
        author: &Requester,
        threshold: usize,
    ) -> Result<EncryptedDocumentKey, Error> {
        // recover requestor' public key from signature
        let public = author
            .public(key_id)
            .map_err(Error::InsufficientRequesterData)?;

        // generate server key
        let server_key = self.generate_key(key_id, author, threshold)?;

        // generate random document key
        let document_key = math::generate_random_point()?;
        let encrypted_document_key = math::encrypt_secret(&document_key, &server_key)?;

        // store document key in the storage
        self.store_document_key(
            key_id,
            author,
            encrypted_document_key.common_point,
            encrypted_document_key.encrypted_point,
        )?;

        // encrypt document key with requestor public key
        let document_key = crypto::ecies::encrypt(&public, &DEFAULT_MAC, &document_key)
            .map_err(|err| Error::Internal(format!("Error encrypting document key: {}", err)))?;
        Ok(document_key)
    }

    fn restore_document_key(
        &self,
        key_id: &ServerKeyId,
        requester: &Requester,
    ) -> Result<EncryptedDocumentKey, Error> {
        // recover requestor' public key from signature
        let public = requester
            .public(key_id)
            .map_err(Error::InsufficientRequesterData)?;

        // decrypt document key
        let decryption_session = self.data.lock().cluster.new_decryption_session(
            key_id.clone(),
            None,
            requester.clone(),
            None,
            false,
            false,
        )?;
        let document_key = decryption_session
            .wait(None)
            .expect("when wait is called without timeout it always returns Some; qed")?
            .decrypted_secret;

        // encrypt document key with requestor public key
        let document_key = crypto::ecies::encrypt(&public, &DEFAULT_MAC, &document_key)
            .map_err(|err| Error::Internal(format!("Error encrypting document key: {}", err)))?;
        Ok(document_key)
    }

    fn restore_document_key_shadow(
        &self,
        key_id: &ServerKeyId,
        requester: &Requester,
    ) -> Result<EncryptedDocumentKeyShadow, Error> {
        let decryption_session = self.data.lock().cluster.new_decryption_session(
            key_id.clone(),
            None,
            requester.clone(),
            None,
            true,
            false,
        )?;
        decryption_session
            .wait(None)
            .expect("when wait is called without timeout it always returns Some; qed")
            .map_err(Into::into)
    }
}

impl MessageSigner for KeyServerImpl {
    fn sign_message_schnorr(
        &self,
        key_id: &ServerKeyId,
        requester: &Requester,
        message: MessageHash,
    ) -> Result<EncryptedMessageSignature, Error> {
        // recover requestor' public key from signature
        let public = requester
            .public(key_id)
            .map_err(Error::InsufficientRequesterData)?;

        // sign message
        let signing_session = self.data.lock().cluster.new_schnorr_signing_session(
            key_id.clone(),
            requester.clone().into(),
            None,
            message,
        )?;
        let message_signature = signing_session.wait()?;

        // compose two message signature components into single one
        let mut combined_signature = [0; 64];
        combined_signature[..32].clone_from_slice(&**message_signature.0);
        combined_signature[32..].clone_from_slice(&**message_signature.1);

        // encrypt combined signature with requestor public key
        let message_signature = crypto::ecies::encrypt(&public, &DEFAULT_MAC, &combined_signature)
            .map_err(|err| {
                Error::Internal(format!("Error encrypting message signature: {}", err))
            })?;
        Ok(message_signature)
    }

    fn sign_message_ecdsa(
        &self,
        key_id: &ServerKeyId,
        requester: &Requester,
        message: MessageHash,
    ) -> Result<EncryptedMessageSignature, Error> {
        // recover requestor' public key from signature
        let public = requester
            .public(key_id)
            .map_err(Error::InsufficientRequesterData)?;

        // sign message
        let signing_session = self.data.lock().cluster.new_ecdsa_signing_session(
            key_id.clone(),
            requester.clone().into(),
            None,
            message,
        )?;
        let message_signature = signing_session.wait()?;

        // encrypt combined signature with requestor public key
        let message_signature = crypto::ecies::encrypt(&public, &DEFAULT_MAC, &*message_signature)
            .map_err(|err| {
                Error::Internal(format!("Error encrypting message signature: {}", err))
            })?;
        Ok(message_signature)
    }
}

impl KeyServerCore {
    pub fn new(
        config: &ClusterConfiguration,
        key_server_set: Arc<dyn KeyServerSet>,
        self_key_pair: Arc<dyn NodeKeyPair>,
        acl_storage: Arc<dyn AclStorage>,
        key_storage: Arc<dyn KeyStorage>,
        executor: Executor,
    ) -> Result<Self, Error> {
        let cconfig = NetClusterConfiguration {
            self_key_pair: self_key_pair.clone(),
            key_server_set: key_server_set,
            acl_storage: acl_storage,
            key_storage: key_storage,
            admin_public: config.admin_public,
            preserve_sessions: false,
        };
        let net_config = NetConnectionsManagerConfig {
            listen_address: (
                config.listener_address.address.clone(),
                config.listener_address.port,
            ),
            allow_connecting_to_higher_nodes: config.allow_connecting_to_higher_nodes,
            auto_migrate_enabled: config.auto_migrate_enabled,
        };

        let core = new_network_cluster(executor, cconfig, net_config)?;
        let cluster = core.client();
        core.run()?;

        Ok(KeyServerCore { cluster })
    }
}

#[cfg(test)]
pub mod tests {
    use super::KeyServerImpl;
    use acl_storage::DummyAclStorage;
    use crypto::DEFAULT_MAC;
    use ethereum_types::{H256, H520};
    use ethkey::{self, crypto, verify_public, Generator, Random, Secret};
    use key_server_cluster::math;
    use key_server_set::tests::MapKeyServerSet;
    use key_storage::{tests::DummyKeyStorage, KeyStorage};
    use node_key_pair::PlainNodeKeyPair;
    use parity_runtime::Runtime;
    use std::{
        collections::{BTreeMap, BTreeSet},
        net::SocketAddr,
        sync::Arc,
        time,
    };
    use traits::{
        AdminSessionsServer, DocumentKeyServer, KeyServer, MessageSigner, ServerKeyGenerator,
    };
    use types::{
        ClusterConfiguration, EncryptedDocumentKey, EncryptedDocumentKeyShadow,
        EncryptedMessageSignature, Error, MessageHash, NodeAddress, NodeId, Public,
        RequestSignature, Requester, ServerKeyId,
    };

    #[derive(Default)]
    pub struct DummyKeyServer;

    impl KeyServer for DummyKeyServer {}

    impl AdminSessionsServer for DummyKeyServer {
        fn change_servers_set(
            &self,
            _old_set_signature: RequestSignature,
            _new_set_signature: RequestSignature,
            _new_servers_set: BTreeSet<NodeId>,
        ) -> Result<(), Error> {
            unimplemented!("test-only")
        }
    }

    impl ServerKeyGenerator for DummyKeyServer {
        fn generate_key(
            &self,
            _key_id: &ServerKeyId,
            _author: &Requester,
            _threshold: usize,
        ) -> Result<Public, Error> {
            unimplemented!("test-only")
        }

        fn restore_key_public(
            &self,
            _key_id: &ServerKeyId,
            _author: &Requester,
        ) -> Result<Public, Error> {
            unimplemented!("test-only")
        }
    }

    impl DocumentKeyServer for DummyKeyServer {
        fn store_document_key(
            &self,
            _key_id: &ServerKeyId,
            _author: &Requester,
            _common_point: Public,
            _encrypted_document_key: Public,
        ) -> Result<(), Error> {
            unimplemented!("test-only")
        }

        fn generate_document_key(
            &self,
            _key_id: &ServerKeyId,
            _author: &Requester,
            _threshold: usize,
        ) -> Result<EncryptedDocumentKey, Error> {
            unimplemented!("test-only")
        }

        fn restore_document_key(
            &self,
            _key_id: &ServerKeyId,
            _requester: &Requester,
        ) -> Result<EncryptedDocumentKey, Error> {
            unimplemented!("test-only")
        }

        fn restore_document_key_shadow(
            &self,
            _key_id: &ServerKeyId,
            _requester: &Requester,
        ) -> Result<EncryptedDocumentKeyShadow, Error> {
            unimplemented!("test-only")
        }
    }

    impl MessageSigner for DummyKeyServer {
        fn sign_message_schnorr(
            &self,
            _key_id: &ServerKeyId,
            _requester: &Requester,
            _message: MessageHash,
        ) -> Result<EncryptedMessageSignature, Error> {
            unimplemented!("test-only")
        }

        fn sign_message_ecdsa(
            &self,
            _key_id: &ServerKeyId,
            _requester: &Requester,
            _message: MessageHash,
        ) -> Result<EncryptedMessageSignature, Error> {
            unimplemented!("test-only")
        }
    }

    fn make_key_servers(
        start_port: u16,
        num_nodes: usize,
    ) -> (Vec<KeyServerImpl>, Vec<Arc<DummyKeyStorage>>, Runtime) {
        let key_pairs: Vec<_> = (0..num_nodes).map(|_| Random.generate().unwrap()).collect();
        let configs: Vec<_> = (0..num_nodes)
            .map(|i| ClusterConfiguration {
                listener_address: NodeAddress {
                    address: "127.0.0.1".into(),
                    port: start_port + (i as u16),
                },
                nodes: key_pairs
                    .iter()
                    .enumerate()
                    .map(|(j, kp)| {
                        (
                            kp.public().clone(),
                            NodeAddress {
                                address: "127.0.0.1".into(),
                                port: start_port + (j as u16),
                            },
                        )
                    })
                    .collect(),
                key_server_set_contract_address: None,
                allow_connecting_to_higher_nodes: false,
                admin_public: None,
                auto_migrate_enabled: false,
            })
            .collect();
        let key_servers_set: BTreeMap<Public, SocketAddr> = configs[0]
            .nodes
            .iter()
            .map(|(k, a)| {
                (
                    k.clone(),
                    format!("{}:{}", a.address, a.port).parse().unwrap(),
                )
            })
            .collect();
        let key_storages = (0..num_nodes)
            .map(|_| Arc::new(DummyKeyStorage::default()))
            .collect::<Vec<_>>();
        let runtime = Runtime::with_thread_count(4);
        let key_servers: Vec<_> = configs
            .into_iter()
            .enumerate()
            .map(|(i, cfg)| {
                KeyServerImpl::new(
                    &cfg,
                    Arc::new(MapKeyServerSet::new(false, key_servers_set.clone())),
                    Arc::new(PlainNodeKeyPair::new(key_pairs[i].clone())),
                    Arc::new(DummyAclStorage::default()),
                    key_storages[i].clone(),
                    runtime.executor(),
                )
                .unwrap()
            })
            .collect();

        // wait until connections are established. It is fast => do not bother with events here
        let start = time::Instant::now();
        let mut tried_reconnections = false;
        loop {
            if key_servers
                .iter()
                .all(|ks| ks.cluster().is_fully_connected())
            {
                break;
            }

            let old_tried_reconnections = tried_reconnections;
            let mut fully_connected = true;
            for key_server in &key_servers {
                if !key_server.cluster().is_fully_connected() {
                    fully_connected = false;
                    if !old_tried_reconnections {
                        tried_reconnections = true;
                        key_server.cluster().connect();
                    }
                }
            }
            if fully_connected {
                break;
            }
            if time::Instant::now() - start > time::Duration::from_millis(3000) {
                panic!("connections are not established in 3000ms");
            }
        }

        (key_servers, key_storages, runtime)
    }

    #[test]
    fn document_key_generation_and_retrievement_works_over_network_with_single_node() {
        let _ = ::env_logger::try_init();
        let (key_servers, _, runtime) = make_key_servers(6070, 1);

        // generate document key
        let threshold = 0;
        let document = Random.generate().unwrap().secret().clone();
        let secret = Random.generate().unwrap().secret().clone();
        let signature = ethkey::sign(&secret, &document).unwrap();
        let generated_key = key_servers[0]
            .generate_document_key(&document, &signature.clone().into(), threshold)
            .unwrap();
        let generated_key = crypto::ecies::decrypt(&secret, &DEFAULT_MAC, &generated_key).unwrap();

        // now let's try to retrieve key back
        for key_server in key_servers.iter() {
            let retrieved_key = key_server
                .restore_document_key(&document, &signature.clone().into())
                .unwrap();
            let retrieved_key =
                crypto::ecies::decrypt(&secret, &DEFAULT_MAC, &retrieved_key).unwrap();
            assert_eq!(retrieved_key, generated_key);
        }
        drop(runtime);
    }

    #[test]
    fn document_key_generation_and_retrievement_works_over_network_with_3_nodes() {
        let _ = ::env_logger::try_init();
        let (key_servers, key_storages, runtime) = make_key_servers(6080, 3);

        let test_cases = [0, 1, 2];
        for threshold in &test_cases {
            // generate document key
            let document = Random.generate().unwrap().secret().clone();
            let secret = Random.generate().unwrap().secret().clone();
            let signature = ethkey::sign(&secret, &document).unwrap();
            let generated_key = key_servers[0]
                .generate_document_key(&document, &signature.clone().into(), *threshold)
                .unwrap();
            let generated_key =
                crypto::ecies::decrypt(&secret, &DEFAULT_MAC, &generated_key).unwrap();

            // now let's try to retrieve key back
            for (i, key_server) in key_servers.iter().enumerate() {
                let retrieved_key = key_server
                    .restore_document_key(&document, &signature.clone().into())
                    .unwrap();
                let retrieved_key =
                    crypto::ecies::decrypt(&secret, &DEFAULT_MAC, &retrieved_key).unwrap();
                assert_eq!(retrieved_key, generated_key);

                let key_share = key_storages[i].get(&document).unwrap().unwrap();
                assert!(key_share.common_point.is_some());
                assert!(key_share.encrypted_point.is_some());
            }
        }
        drop(runtime);
    }

    #[test]
    fn server_key_generation_and_storing_document_key_works_over_network_with_3_nodes() {
        let _ = ::env_logger::try_init();
        let (key_servers, _, runtime) = make_key_servers(6090, 3);

        let test_cases = [0, 1, 2];
        for threshold in &test_cases {
            // generate server key
            let server_key_id = Random.generate().unwrap().secret().clone();
            let requestor_secret = Random.generate().unwrap().secret().clone();
            let signature = ethkey::sign(&requestor_secret, &server_key_id).unwrap();
            let server_public = key_servers[0]
                .generate_key(&server_key_id, &signature.clone().into(), *threshold)
                .unwrap();

            // generate document key (this is done by KS client so that document key is unknown to any KS)
            let generated_key = Random.generate().unwrap().public().clone();
            let encrypted_document_key =
                math::encrypt_secret(&generated_key, &server_public).unwrap();

            // store document key
            key_servers[0]
                .store_document_key(
                    &server_key_id,
                    &signature.clone().into(),
                    encrypted_document_key.common_point,
                    encrypted_document_key.encrypted_point,
                )
                .unwrap();

            // now let's try to retrieve key back
            for key_server in key_servers.iter() {
                let retrieved_key = key_server
                    .restore_document_key(&server_key_id, &signature.clone().into())
                    .unwrap();
                let retrieved_key =
                    crypto::ecies::decrypt(&requestor_secret, &DEFAULT_MAC, &retrieved_key)
                        .unwrap();
                let retrieved_key = Public::from_slice(&retrieved_key);
                assert_eq!(retrieved_key, generated_key);
            }
        }
        drop(runtime);
    }

    #[test]
    fn server_key_generation_and_message_signing_works_over_network_with_3_nodes() {
        let _ = ::env_logger::try_init();
        let (key_servers, _, runtime) = make_key_servers(6100, 3);

        let test_cases = [0, 1, 2];
        for threshold in &test_cases {
            // generate server key
            let server_key_id = Random.generate().unwrap().secret().clone();
            let requestor_secret = Random.generate().unwrap().secret().clone();
            let signature = ethkey::sign(&requestor_secret, &server_key_id).unwrap();
            let server_public = key_servers[0]
                .generate_key(&server_key_id, &signature.clone().into(), *threshold)
                .unwrap();

            // sign message
            let message_hash = H256::from(42);
            let combined_signature = key_servers[0]
                .sign_message_schnorr(&server_key_id, &signature.into(), message_hash.clone())
                .unwrap();
            let combined_signature =
                crypto::ecies::decrypt(&requestor_secret, &DEFAULT_MAC, &combined_signature)
                    .unwrap();
            let signature_c = Secret::from_slice(&combined_signature[..32]).unwrap();
            let signature_s = Secret::from_slice(&combined_signature[32..]).unwrap();

            // check signature
            assert_eq!(
                math::verify_schnorr_signature(
                    &server_public,
                    &(signature_c, signature_s),
                    &message_hash
                ),
                Ok(true)
            );
        }
        drop(runtime);
    }

    #[test]
    fn decryption_session_is_delegated_when_node_does_not_have_key_share() {
        let _ = ::env_logger::try_init();
        let (key_servers, key_storages, runtime) = make_key_servers(6110, 3);

        // generate document key
        let threshold = 0;
        let document = Random.generate().unwrap().secret().clone();
        let secret = Random.generate().unwrap().secret().clone();
        let signature = ethkey::sign(&secret, &document).unwrap();
        let generated_key = key_servers[0]
            .generate_document_key(&document, &signature.clone().into(), threshold)
            .unwrap();
        let generated_key = crypto::ecies::decrypt(&secret, &DEFAULT_MAC, &generated_key).unwrap();

        // remove key from node0
        key_storages[0].remove(&document).unwrap();

        // now let's try to retrieve key back by requesting it from node0, so that session must be delegated
        let retrieved_key = key_servers[0]
            .restore_document_key(&document, &signature.into())
            .unwrap();
        let retrieved_key = crypto::ecies::decrypt(&secret, &DEFAULT_MAC, &retrieved_key).unwrap();
        assert_eq!(retrieved_key, generated_key);
        drop(runtime);
    }

    #[test]
    fn schnorr_signing_session_is_delegated_when_node_does_not_have_key_share() {
        let _ = ::env_logger::try_init();
        let (key_servers, key_storages, runtime) = make_key_servers(6114, 3);
        let threshold = 1;

        // generate server key
        let server_key_id = Random.generate().unwrap().secret().clone();
        let requestor_secret = Random.generate().unwrap().secret().clone();
        let signature = ethkey::sign(&requestor_secret, &server_key_id).unwrap();
        let server_public = key_servers[0]
            .generate_key(&server_key_id, &signature.clone().into(), threshold)
            .unwrap();

        // remove key from node0
        key_storages[0].remove(&server_key_id).unwrap();

        // sign message
        let message_hash = H256::from(42);
        let combined_signature = key_servers[0]
            .sign_message_schnorr(&server_key_id, &signature.into(), message_hash.clone())
            .unwrap();
        let combined_signature =
            crypto::ecies::decrypt(&requestor_secret, &DEFAULT_MAC, &combined_signature).unwrap();
        let signature_c = Secret::from_slice(&combined_signature[..32]).unwrap();
        let signature_s = Secret::from_slice(&combined_signature[32..]).unwrap();

        // check signature
        assert_eq!(
            math::verify_schnorr_signature(
                &server_public,
                &(signature_c, signature_s),
                &message_hash
            ),
            Ok(true)
        );
        drop(runtime);
    }

    #[test]
    fn ecdsa_signing_session_is_delegated_when_node_does_not_have_key_share() {
        let _ = ::env_logger::try_init();
        let (key_servers, key_storages, runtime) = make_key_servers(6117, 4);
        let threshold = 1;

        // generate server key
        let server_key_id = Random.generate().unwrap().secret().clone();
        let requestor_secret = Random.generate().unwrap().secret().clone();
        let signature = ethkey::sign(&requestor_secret, &server_key_id).unwrap();
        let server_public = key_servers[0]
            .generate_key(&server_key_id, &signature.clone().into(), threshold)
            .unwrap();

        // remove key from node0
        key_storages[0].remove(&server_key_id).unwrap();

        // sign message
        let message_hash = H256::random();
        let signature = key_servers[0]
            .sign_message_ecdsa(&server_key_id, &signature.into(), message_hash.clone())
            .unwrap();
        let signature =
            crypto::ecies::decrypt(&requestor_secret, &DEFAULT_MAC, &signature).unwrap();
        let signature: H520 = signature[0..65].into();

        // check signature
        assert!(verify_public(&server_public, &signature.into(), &message_hash).unwrap());
        drop(runtime);
    }

    #[test]
    fn servers_set_change_session_works_over_network() {
        // TODO [Test]
    }
}