COBRA is a fully-featured state machine replication library that guarantees the confidentiality of the data. Confidentiality is ensured by integrating a secret sharing mechanism into the modified BFT-SMaRt library, a fully-featured replication library without confidentiality guarantees. You can find the modified version of the BFT-SMaRt library here.

This library is a proof-of-concept implementation and not a production-ready implementation. Therefore, before using it, consider the following limitations:

• The periodic execution of the resharing protocol is disabled. It can be activated but requires hardcoding the number of shares to reshare;
• The constant commitment scheme, i.e., Kate et al.'s protocol, was not tested with recent changes;
• The adversarial attack for resharing is hardcoded in branches adversarial_1_faulty_servers, adversarial_2_faulty_servers, and adversarial_3_faulty_servers;
• Recovery and resharing while changing the leader was not tested.

The COBRA library is primarily implemented in Java and currently uses Gradle to compile, package, and deploy compiled code for local testing. Nevertheless, we use C to implement the constant commitment scheme functions and call those functions in Java through Java Native Interface.

The current COBRA library was tested using Java 11.0.13.

First, clone this repository. Now inside the COBRA folder (assuming you did not change the name), follow the following instructions depending on the intended result.

There are two ways to compile and package the COBRA library:

• Compile and package the library: Execute ./gradlew installDist. The required jar files and default configurations files will be available inside the build/install/COBRA folder.
• Compile and package to locally test the library: Execute ./gradlew localDeploy. The execution of Gradle task localDeploy will create the folder build/local containing nServers folders rep* and nClients folders cli* (you can change these parameters in the build.gradle file). Each server and client folder will have the required files to run COBRA demos.

Compiling C code

The constant commitment scheme is implemented in C using relic library. Execute the following commands inside pairing folder to compile the relic library and C code:

1. Compile the relic library by executing ./build_relic.sh;
2. Compile the C code by executing ./build.sh <path to java folder>.

Since COBRA extends the BFT-SMaRt library, first configure BFT-SMaRt following instructions presented in its repository. Then configure COBRA's behaviour by modifying the config/cobra.config file.

TIP: Reconfigure the system before compiling and packaging. This way, you don't have to configure multiple replicas.

NOTE: Following commands considers the Linux operating system. For the Windows operating system, use script run.cmd instead of ./smartrun.sh.

Running the map demo (4 replicas tolerating 1 fault):

Execute the following commands across four different server consoles from within the folders build/local/rep*:

build/local/rep0$./smartrun.sh confidential.demo.map.server.Server 0
build/local/rep1$./smartrun.sh confidential.demo.map.server.Server 1
build/local/rep2$./smartrun.sh confidential.demo.map.server.Server 2
build/local/rep3$./smartrun.sh confidential.demo.map.server.Server 3

Once all replicas are ready, the client can be launched by executing the following command in directory build/local/cli0/:

build/local/cli0$./smartrun.sh confidential.demo.map.client.Client 100

Running throughput and latency experiment:

After compiling and packaging, copy the content of the COBRA/build/install/COBRA folder into different locations/servers. Next, we present an example of running a system with four replicas tolerating one fault.

Execute the following commands across four different server consoles:

./smartrun.sh confidential.benchmark.ThroughputLatencyKVStoreServer 0
./smartrun.sh confidential.benchmark.ThroughputLatencyKVStoreServer 1
./smartrun.sh confidential.benchmark.ThroughputLatencyKVStoreServer 2
./smartrun.sh confidential.benchmark.ThroughputLatencyKVStoreServer 3

Once all replicas are ready, you can launch clients by executing the following command:

./smartrun.sh confidential.benchmark.PreComputedKVStoreClient <initial client id> <num clients> <number of ops> <request size> <write?> <precomputed?> <measurement leader?>

where:

• <initial client id> - the initial client id, e.g, 100;
• <num clients> - the number clients each execution of command will create, e.g., 20;
• <number of ops> - the number of requests each client will send, e.g., 10000;
• <request size> - the size in byte of each request, e.g., 1024;
• <write?> - requests are of write or read type? E.g., true;
• <precompute?> - are the requests precompute before sending to servers or are created on fly? E.g., true;
• <measurement leader?> - will this client print the latencies? E.g., true.

Interpreting the throughput and latency results

When clients continuously send the requests, servers will print the throughput information every two seconds. When a client finishes sending the requests, it will print a string containing space-separated latencies of each request in nanoseconds. For example, you can use this result to compute average latency.

Branches adversarial_1_faulty_servers, adversarial_2_faulty_servers, and adversarial_3_faulty_servers have hardcoded demonstration of the effect of 1, 2, and 3 faulty servers, respectively, during resharing in a system with ten replicas tolerating three faults.

In all demonstrations, replica 1 acts maliciously during resharing and send an invalid resharing polynomial proposal to replica 2. When this happens, replica 2 will receive an invalid share on the de-blinding polynomial needed to reconstruct its renewed share. Replica 2 starts executing the recovery protocol to recover its valid share.

During the execution of the recovery protocol, replica 1 sends an invalid recovery polynomial proposal to replica 3, which jeopardizes the recovery. Servers collectively remove replica 1, and replica 2 successfully recovers its share during the second execution of the recovery protocol. This scenario is demonstrated in the branch adversarial_1_faulty_servers.

In the scenario of a branch adversarial_2_faulty_servers, replica 4 sends an invalid recovery polynomial proposal to replica 3, which compromise the second recovery attempt. Again, after the remaining servers collectively remove replica 4, replica 2 successfully recovers its share during the third attempt.

Finally, in the third branch, adversarial_3_faulty_servers, replica 5 compromise the third recovery attempt, which is also removed by the servers. During the fourth recovery attempt, replica 2 successfully recovers its share on resharing polynomial.

You can test these demonstrations by following these instructions:

1. Clone the repository from the respective branch;
2. Start replicas by executing the following commands in consoles opened in each of build/local/rep* folder:

   build/local/rep0$./smartrun.sh confidential.benchmark.ThroughputLatencyKVStoreServer 0
   build/local/rep1$./smartrun.sh confidential.benchmark.ThroughputLatencyKVStoreServer 1
   build/local/rep2$./smartrun.sh confidential.benchmark.ThroughputLatencyKVStoreServer 2
   build/local/rep3$./smartrun.sh confidential.benchmark.ThroughputLatencyKVStoreServer 3
   build/local/rep4$./smartrun.sh confidential.benchmark.ThroughputLatencyKVStoreServer 4
   build/local/rep5$./smartrun.sh confidential.benchmark.ThroughputLatencyKVStoreServer 5
   build/local/rep6$./smartrun.sh confidential.benchmark.ThroughputLatencyKVStoreServer 6
   build/local/rep7$./smartrun.sh confidential.benchmark.ThroughputLatencyKVStoreServer 7
   build/local/rep8$./smartrun.sh confidential.benchmark.ThroughputLatencyKVStoreServer 8
   build/local/rep9$./smartrun.sh confidential.benchmark.ThroughputLatencyKVStoreServer 9
   

3. Once all the replicas are ready, execute the following command inside the folder build/local/cli0/:

   build/local/cli0$./smartrun.sh confidential.benchmark.PreComputedKVStoreClient 100 1 1 1024 true true false
   

4. When the previous client terminates, execute the following command inside the folder build/local/cli0/:

   build/local/cli0$./smartrun.sh confidential.reconfiguration.ReconfigurationClient 7002 config/reconfiguration_f_3.json
   

The last step (Step 4) execution will trigger resharing protocols in servers. Depending on the branch, replica 2 will end resharing its state after the second, third, or fourth recovery attempt and will show the total resharing cost in milliseconds of resharing shares of one secret. To observe the positive impact of our protocol when resharing multiple secret shares with the influence of an adversary, in Step 3 execute:

build/local/cli0$./smartrun.sh confidential.benchmark.PreComputedKVStoreClient 100 1 1000 1024 true true false

Following are the relevant modifications done in BFT-SMaRt:

• Invoking ordered and unordered operations with distinct public and private parts of requests;
• Temporarily storing private state (i.e., shares) in ClientData during the consensus execution;
• Checking proposed value during the consensus execution;
• Added a metadata field inside MessageContext and TOMMessage;
• Added a reconfiguration listener.

We empirically showed that the COBRA library improves the state-of-the-art protocol VSSR in recovery and the state-of-the-art protocol MPSS in resharing. The prototype implementation of VSSR and MPSS can be found here and here, respectively.

Feel free to contact us if you have any questions!