ZkpSharp

A .NET library for Zero-Knowledge Proofs with Stellar Soroban blockchain integration. Prove facts about private data (age, balance, membership, range, time conditions) without revealing the data itself.

Features

Privacy proofs (HMAC-based commitment schemes) -- fast, lightweight:

• Proof of Age, Balance, Membership, Range, Time Condition
• HMAC-SHA256 with cryptographic salt

True zero-knowledge proofs (Bulletproofs) -- mathematically sound:

• ZK range, age, and balance proofs using Pedersen commitments
• Compact serialization for storage and transmission

Stellar blockchain integration:

• Soroban SDK 25 with BLS12-381 cryptography
• On-chain verification via InvokeHostFunctionOp
• SorobanTransactionBuilder for XDR construction

Installation

dotnet add package ZkpSharp

Quick start

using ZkpSharp.Core; using ZkpSharp.Security; var proofProvider = new ProofProvider("your-base64-encoded-32-byte-key"); var zkp = new Zkp(proofProvider); // Prove age >= 18 without revealing birthdate var (proof, salt) = zkp.ProveAge(new DateTime(1995, 3, 15)); bool valid = zkp.VerifyAge(proof, new DateTime(1995, 3, 15), salt); // Prove sufficient balance without revealing actual amount var (bProof, bSalt) = zkp.ProveBalance(1000.0, 500.0); bool bValid = zkp.VerifyBalance(bProof, 500.0, bSalt, 1000.0);

For Bulletproofs (true ZKP):

using ZkpSharp.Security; var zkProvider = new BulletproofsProvider(); var (proof, commitment) = zkProvider.ProveRange(value: 42, min: 0, max: 100); bool valid = zkProvider.VerifyRange(proof, commitment, min: 0, max: 100);

See QUICKSTART.md for a complete walkthrough including Stellar integration.

API

Zkp -- HMAC-based privacy proofs

Method	Description
ProveAge(DateTime dateOfBirth)	Prove age >= 18 (configurable)
VerifyAge(string proof, DateTime dateOfBirth, string salt)	Verify age proof
ProveBalance(double balance, double requestedAmount)	Prove balance >= requested
VerifyBalance(string proof, double requestedAmount, string salt, double balance)	Verify balance proof
ProveMembership(string value, string[] validValues)	Prove value is in set
VerifyMembership(string proof, string value, string salt, string[] validValues)	Verify membership proof
ProveRange(double value, double minValue, double maxValue)	Prove value is in range
VerifyRange(string proof, double minValue, double maxValue, double value, string salt)	Verify range proof
ProveTimeCondition(DateTime eventDate, DateTime conditionDate)	Prove event after date
VerifyTimeCondition(string proof, DateTime eventDate, DateTime conditionDate, string salt)	Verify time proof

All Prove* methods return (string Proof, string Salt). Salts are generated automatically and must be stored alongside proofs.

BulletproofsProvider -- True zero-knowledge proofs

Method	Description
ProveRange(long value, long min, long max)	ZK range proof
VerifyRange(byte[] proof, byte[] commitment, long min, long max)	Verify ZK range proof
ProveAge(DateTime birthDate, int minAge)	ZK age proof
VerifyAge(byte[] proof, byte[] commitment, int minAge)	Verify ZK age proof
ProveBalance(long balance, long requiredAmount)	ZK balance proof
VerifyBalance(byte[] proof, byte[] commitment, long requiredAmount)	Verify ZK balance proof
SerializeProof(byte[] proof, byte[] commitment)	Serialize for storage
DeserializeProof(string serialized)	Deserialize proof

Prove* methods return (byte[] proof, byte[] commitment).

StellarBlockchain -- On-chain verification

var blockchain = new StellarBlockchain( serverUrl: "https://horizon-testnet.stellar.org", sorobanRpcUrl: "https://soroban-testnet.stellar.org", hmacKey: hmacKey ); bool result = await blockchain.VerifyBalanceProof(contractId, proof, balance, required, salt);

SorobanTransactionBuilder -- Manual transaction construction

var builder = new SorobanTransactionBuilder(Network.Test()); // HMAC proof verification string xdr = builder.BuildVerifyProofTransaction(contractId, proof, data, salt, hmacKey); // ZK proof verification string zkXdr = builder.BuildVerifyZkRangeProofTransaction(contractId, proof, commitment, min, max); string ageXdr = builder.BuildVerifyZkAgeProofTransaction(contractId, proof, commitment, minAge); string balXdr = builder.BuildVerifyZkBalanceProofTransaction(contractId, proof, commitment, required);

Soroban contract

The Rust smart contract (contracts/stellar/contracts/proof-balance/) exposes the following functions:

Function	Description
verify_proof	HMAC-SHA256 proof verification
verify_balance_proof	Balance proof with numeric comparison
verify_batch	Batch verification of multiple proofs
verify_zk_range_proof	BLS12-381 ZK range verification
verify_zk_age_proof	ZK age verification
verify_zk_balance_proof	ZK balance verification

See contracts/stellar/README.md for contract details and contracts/stellar/DEPLOYMENT.md for deployment instructions.

Architecture

Application | +-- Zkp (HMAC proofs) +-- BulletproofsProvider (ZK proofs) | +-- StellarBlockchain +-- SorobanTransactionBuilder --> XDR +-- SorobanRpcClient --> Soroban RPC --> ZkpVerifier Contract

Security

• Key management: Use environment variables for development. Use Azure Key Vault, AWS Secrets Manager, or HashiCorp Vault in production.
• Salts: Never reuse. ZkpSharp generates cryptographically secure random salts automatically.
• Contract verification: Always verify deployed contract code matches source.
• Transaction fees: Soroban transactions require XLM.

Documentation

Document	Description
QUICKSTART.md	Step-by-step setup and usage guide
DEPLOYMENT.md	Soroban contract deployment
STELLAR_REALITY_CHECK.md	Capabilities and limitations
INTEGRATION_STATUS.md	Feature status and migration guide
CHANGELOG.md	Version history

Contributing

1. Fork the repository
2. Create a branch (git checkout -b feature/your-feature)
3. Run tests (dotnet test)
4. Submit a pull request

License

MIT License. See LICENSE for details.

Contact

sagynbaev6@gmail.com | GitHub Issues | NuGet